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Joined: September 6, 2009

What's the deal with your nickname? How did you get it? If your nickname is self-explanatory, then tell everyone when you first started using the internet, and what was the first thing that made you say "wow, this isn't just a place for freaks after all?" Was it a website? Was it an email from a long-lost friend? Go on, spill it.

No one reads down here I guess.
Empty or full, always the same
No target— no notice, no aim
Sometimes it seems like pointlessly
filling a void
Other times it's finding a million miles of indifference to avoid.

I hope you are doing well.
Hello :)

Easier to post more of the links on
Twitter @CriticalOptMism

I biked across a large bit of Quebec along the Route Verte August 2014. See Flickr for some pictures navigate like a time lapse. Use arrows.
Quebec was unbelievably bike friendly. If you cycle try Quebec for an amazing ride. Respected by drivers the whole way. But an amazing amount was bike only paths. Total ride was about 500 km total. Cargo bike carrying about 150 lbs cargo. Tent etc.

I started in Ottawa, crossing over, and then following the RouteVerte edging around Montreal, and getting to ~Bertierville before it turned into a bunch of days of rain in a row.
Oh, looking through the pictures made me have memories, will write about it there...
http://www.studentdigitalus.org/RouteVerte/
instead of here. Actually I kind of love these profiles, very extendable, and like, maybe I will make posts to here from now on.

Flikr RouteVerte Album All images:
https://www.flickr.com/photos/42297742@N07/sets/72157650603167039/

Next year aka this year I will get further. Or travel farther.
Bonne Chance.

SCRATCH THAT!
Not able to make long bike trip this summer... Because I will be travelling a great distance for a new job!!

After a year of applying. Yahoo!
(It is not a position with Yahoo!)

Meetups? Never done that. I don't know people who know people.



NOTE: all my websites are terrible, and in progress, but they are my websites.


Cold War/NORAD stuff:
https://www.flickr.com/photos/42297742@N07/sets/72157627518327509/

http://studentdigitalus.org
http://studentdigitalus.org/IndigenousColonialBanana/

http://studentdigitalus.org/HistoriesofIslamicCivilizations/

http://studentdigitalus.org/ForensicStories_MedicolegalContexts/

http://studentdigitalus.org/EducationIssuesToday/

http://studentdigitalus.org/ConnectRussia/

http://studentdigitalus.org/CanadianTimescapes/

http://studentdigitalus.org/TajikistanFocus/





Xenos'-Phobia... from boyzone to racism to Homophobia to sexism and Islamophobia, because everytime a discussion is had, the Overton window shifts half-way towards openness, and free exchange of dialogue... but the problem is that it is always half way. And if you travel exactly half way to progress forever.... you still shall not have arrived at "progress".

Re-reading this it isn't ever actually even close to halfway that we shift towards progress, more like minimum possible measure... a Planck Length of Progress if you will.

Just know that maybe you can change the world. Your words out there have changed me.

_____________
|-----------------
∞intimation∞
|----------------
[_______________

Infinity;
(symbolically represented with ∞) comes from the Latin infinitas or 'unboundedness' It refers to several distinct concepts – usually linked to the idea of "without end" – which arise in philosophy, mathematics, and theology.

I like to centre this on the realm of thought, creativity, and openness to new ideas, the ability to synthesize two disparate concepts and to construct new things from those simple ideas.

In telling stories we can create the very future of the world around us.

Oneday I'd love to write something that actually interests others.

______________________________________
Vicious-vicious visions of the violently viscous meniscus, light turns dark so we blink, tears flow then dry though our thoughts still may sink—so now think quick thick liquid.
Words; like ink, flow out of this fluid space, so boring, my thoughts are nothing more than insipid—inspired, so tired, an explorer-intrepid, but I'm still no more than running empty, vapid, just a vapor, I'm like liquid yr' solid, yr' going, I'm halted. I'm running away, while yr' still more than totally exalted. No common frame of reference, just a referee, and you, you and me, time for today,... but no excuse for the future, seal this suture, super glue around this fracture. Before it's all over, just leave me a picture.

set sail, til your heart bursts open as if it were impaled. face turn'd pale, arms tingle and your intentions entangle, together as friends let your minds mingle, each moment we share should be seen as single; eyes wide and heart so scared, where are those lost moments from the foot of the wide set stair, i didn't mean to stare, but this was a dream beyond rational compare; so say it all with no rhyme, rhythm, no flair.just.bare.

I stand, captured and caught up, a fixture of our conversations get's brought up, no time like the present, to start setting new precedents, reveal the practice of prejudice, bring up the tales of all of our presidents. Cut back, rattle and rock, till the morning light, & the sound of this shock wave, going knock, knock, so many lost, so many scared, yet so many so brave..crest fallen we must ride out this wave, stay still, stay strong, carry on, move along, nothing2see. Just you and me, and some boxes that arewere empty.

Meh. The power and choice to act or sit silent is your own alone. I cannot make you take one thorough consideration of any care or thought, about anything in concepts mind mapped to impractical fractals late actively adopt.

A Universal Love is in yr' hands ... this is just an intimation.
This is an intimate infinite.intimation.
a barely political notion for such a wizened nation.not aught, though more concept based than most would have thought.highly political, non-partisan, pro-document-based government. (these days I guess it is needed to explain that no, this does not mean 'go tea party'.

Money, power, fame, talent... all are limited, all are finite.
When one allows all desire and single mindedness to fall away besides love. besides inner and outward compassion, the possibilities and potential for cooperative action are Unbounded and Infinite.

Peace.Love.Infinite.Intimation.

To be clear that is intended as an infinitely aspirational assertion, most of the time I am hating my own thoughts, and quietly listening to the sounds of thundering silence, and wishing I could go back and have been a better student in elementary science.



Introduction
One inherently negative aspect of fieldwork in archaeology is that excavation is a “destructive” event. The site excavators, no matter how careful and well trained they may be, are removing the layers that give context to a site, and disturb the provenances within a site. These features and concurrent context will be forever lost--- unavailable to future researchers, who may have been able to glean more from the site than the person who carried out the excavation (e.g. see Nickens 1991). More is lost as the backhoe is brought in to “clear” some of the area so that a few small sub-quadrats can be carefully dissected with hand trowels and horsehair brushes. From this perspective, traditional methods represent a very crude approach to exploration of such precious sites, in that the investigator has to use some judgment on where to focus, discarding much of the potential search area as they follow proper statistical sub-sampling procedures (Fagan and DeCorse 2005 pp177-181). Inevitably, the sample will be only part of the story, and the exploration may be at the wrong scale to represent how the space was actually used. The traditional “dig” will not only destroy potential, scientifically vital, elements of the original context, but it will erase that potential archaeological data from the record forever.

This paper will explore the proposition that we should place more emphasis on digital techniques that would allow us to replace, or at least augment, this destructive, limited, “one time only” style of research, and investigation, as in forensic CSI, with an array of tools including digital, optical, and even simple hand drawn field sketches. We should integrate the wide array of digital techniques that exist today and share data in common formats so that the modern archaeologist and all who follow, including members of the public, will have the ability to understand the context and provenance of sites that we will preserve, rather than tear apart (Nickens 1991). There are a number of exciting techniques available or in development for visualizing of sites and perceiving subtle features within landscapes and of transposing them into hypermedia. There are problems and challenges encountered when navigating, recording, and analyzing forms of landscape-related artifacts such as prehistoric “monuments”, land art, sculpture parks, and landscaped gardens (Fagan and DeCorse 2005 p 201). In particular, techniques will be discussed for examining and recording both the local properties, including texture, form, weathering, and construction techniques of sites, and the wider attributes such as relationship of artifacts to their site, topography, relationships between surrounding sites, and geological context.

It is widely recognized that much important archaeological information is buried in storage facilities and in yellowing, unpublished field notes (Banning 2000, p132); I would argue that geo-referenced digital databases are exactly what we need to catalog the work and discoveries that have already been made, while we develop the tools to correlate, integrate, and speculate on our past, and perhaps find our way into the future on this planet.

Not incidentally, of course, digital media present archaeologists with an excellent opportunity to bring the public “on board” to support the conservation of archaeological sites in the same way as popularization of biology and ecology has led to an awareness and interest in protecting the biodiversity of the rain forest and endangered species. This could help stem the tide of construction and development that irrevocably disturbs sites of great potential importance. If members of the public could take virtual tours of the impressive archaeological sites both as they are now, and as they were at the time they were built and in use, that could reignite a passion and curiosity about humanities origins. Both the “community learning” aspect of “digital archaeology” and preservation of cultural heritage will also be further discussed.
.......
Dead Link to essay I researched and wrote up on what I have great hope that The Google will do one day; please say yes, for a vote for sooner.) to see in the future of Archaeology (and open museums.)
(includes citation of many resources for further research.apologies for any insufferable writing.)

Q: I wonder how accurate carbon dating is?
A: Mostly depends on the context of the site... Mostly.

Re:I wonder how accurate carbon dating is?
A:depends on the context of the site.

Anthropological/archaeological applications, sources of error and other considerations
There have been concerns over the assumption that there is a constant rate of generation of 14Carbon, particularly since the era of atmospheric nuclear bomb tests. These nearly doubled the abundance of radiocarbon in the atmosphere in the mid-1960s. Since then the concentration has been falling, and will in a few years (probably within the next decade) fall to the pre-bomb values (Bronk Ramsey 2008). Interestingly the elevated 14C in marine systems has been used to verify age estimates of long-lived fish based on analysis of fish otoliths (ear bones), which have annual growth rings similar to those in trees (Kalish 1995).

Other sources of variation in 14C production would be variations in the cosmic ray flux, which in turn is affected by changes in the Earth’s magnetic field. There have been several attempts to measure the rate of production of radiocarbon, leading to the conclusion that a rate of 2-3 14C atoms cm-2 s-1 (atoms per square centimeter per second) is reasonable, but Bronk Ramsey et al. (2007) have explored the rate of production of radiocarbon in the atmosphere, and Mak et al. (1999) have done the same at ground level, and there are very different values in these two locations. Bronk Ramsey (2008) points out however that we don’t need to know the rate of production to carry out radiocarbon dating; we need to be aware that the rate will have varied on a range of timescales, and for dating within a century or so, we only need to know the concentration in the atmosphere.

Materials can change over time; indeed even during the life of an organism, its living tissues are constantly turning over. Once an organism dies, breakdown occurs rapidly and usually little remains after a few years. However, in some conditions (e.g. waterlogged deposits and very dry conditions), there is better preservation. This is of course exceptional, so groupings of organisms in a site will not necessarily represent their original assemblages (e.g., in terms of biodiversity or co-occurrences in life). Exactly what survives in the ground and how it does so, is a complex topic. For example, in acidic peat deposits there may be virtually no mineral components remaining but organic preservation may be very good (e.g., the “bog people” preserved in Denmark and other areas in Northern Europe). In hot dry conditions the reverse is likely to be true, with very good mineral preservation and poor preservation of proteins (Hedges and van Klinken 1992). Ultimately, remains of this sort become fossilized, with full replacement of the original material by minerals from the surrounding matrix. Even before this happens, the mineral components of bone and shell often exchange carbon with dissolved carbonate, and so may not retain the original radiocarbon ratio signal (Bronk Ramsey 2008). It is worth noting that this generalization does not match with the findings cited earlier by Spalding et al. (2005).

Additional factors that can affect the accuracy of radiocarbon dating include contamination of the original sample with more recent materials, particularly following acid/base/acid pretreatment (Bronk Ramsey et al. 2004b). For example, bone, as a complex sample material, is routinely used in radiocarbon dating. Prior to carrying out AMS (as first developed by Linick et al. 1989) pre-treatment of the material is important, and that has been an area of ongoing method refinement with many improvements occurring through the work of Bronk Ramsey and his collaborators. According to Bronk Ramsey et al. (2004b), the most effective method of pretreatment for dating many samples has been a simple demineralization, which is effective at removing the most ubiquitous contaminants. An acid/base/acid treatment also removes humic contaminants which can be a significant source of error in many organic-rich contexts. However, these treatments leave behind many organic molecules from the soil and degraded protein fragments, making the sample susceptible to contamination (and under-aging).

Theoretical challenges with 14C dating
Bronk Ramsey (2008) pointed out a number of challenges that may affect the accuracy of the radiocarbon dating methods in use today. Note that these concerns are issues that will affect the accuracy, rather than the precision of the method; there is no doubt that the adoption of AMS has greatly increased the precision of measurements made. However, for radiocarbon dating to be reliable a number of assumptions are made.

Firstly, Libby assumed that 14C decays at a constant rate. However, the accuracy behind 14C dating requires that there is the same rate of cosmic production of radioactive isotopes throughout time, and some experimental evidence pointed to a possibility for interaction in the decay rates of other atoms. The industrial revolution released hundreds of thousands of tons of carbon gases into the atmosphere, increasing the relative proportion of 12C. Furthermore, atmospheric testing of atomic weapons increased neutron levels, raising 14C, so there does not appear to be a constant background (atmospheric) ratio. Thirdly, the environment in which the artifact lies significantly affects the rate of decay. For example, 14C leaches faster from organic material saturated in water, especially saltwater. Fourthly, for 14C to be measured accurately the archaeological artifact must have been protected from contamination. Organic matter, being porous, can easily be contaminated by organic carbon in groundwater. This increases the 12C content and affects the carbon isotope ratio (Bronk Ramsey 2008).

Variations in production rate of 14C can also be attributed to changes in the stream of cosmic rays hitting the Solar System, and due to variations in the Earth’s magnetic field that shields the Earth from the charged particles. On the timescales involved in radiocarbon dating, we would expect the overall cosmic ray flux to the solar system to remain fairly constant, although there may be individual events (such as supernovae) that do occasionally contribute significantly (Damon et al. 1995). This screening effect is in turn affected by solar activity and by the primary strength and direction of the magnetic field itself, and these can lead to very significant variations in radiocarbon production rates. This reaction takes place largely in the upper atmosphere, where thermal neutrons, resulting from a cascade of reactions from cosmic rays, react with the nitrogen atoms in air. Some production is also possible even at ground level, but the rates are about two orders of magnitude lower (Mak et al. 1999), at about 1 x 10-4 atoms g-1 s-1 (atoms per gram per second) or virtually statistically insignificant.

In theory, it could undermine the interpretation of radiocarbon data, if radiocarbon is being formed in situ at ground level. The processes involved are very complex because of moderation of neutrons and attenuation of cosmic rays, and the fact that other production reactions involving oxygen (and therefore oxidation levels) are also possible. However, Bronk Ramsey (2008) argued that in situ production of 14C should not normally be a significant issue in dating unless there is exposure to high neutron doses from other sources.

Comparisons with records of past radiocarbon concentration
If we can establish the compartment in the carbon cycle from which the carbon in a sample was taken, we are able to modify our expectation of starting ratios of Carbon isotopes, and make our measurement in the light of knowledge of the past environment and the decay rate of radiocarbon. Otherwise we can make “reasonable assumptions” (e.g., that the past radiocarbon ratio was as it was in 1950), and use our estimates of the half-life of radiocarbon to estimate the age of the sample. With such an estimate it is very difficult to give statistical confidence limits.

Ideally, we should have material of known age whose carbon is drawn from the same pool as our sample. This is true for the atmosphere in the period where we have wood that has been dated dendrochronologically (using tree rings) as well as with 14C (Reimer et al. 2004). Also, since 1950, we have data on direct atmospheric measurements (Hua and Barbetti 2004). In these cases all we need to do is to compare the radiocarbon measurement for our sample with the reference measurements. In practice, rather than comparing directly to the individual measurements, we put together a radiocarbon calibration curve that gives our best estimate (with quantified uncertainties) for the measurement that we would get for a sample of any age within the range of the data (Buck and Blackwell 2004). In his review, Mellars (2006) has cited improvements in the calibration of radiocarbon time as the most important recent breakthrough, and indeed it provided improvements that are particularly useful to archaeology. The revised calibration showed that there had been a rapid change in radiocarbon ages over the period 40,000-35,000 radiocarbon years ago. This was due to rapid changes in 14C content of the atmosphere over that period. The net result is that dates that covered an apparent 5,000 years actually only covered 3,000 years. Fortunately what this does is to give us greater dating precision for a very important time period in human evolution and dispersal.

Such radiocarbon calibration curves are typically expressed in terms of radiocarbon years except for the period after 1950, but it is better both conceptually and mathematically to consider them as a “fractionation-corrected” isotope ratio or “F14C”. In terms of the algorithms for calibration, this makes almost no difference until the measurements approach background levels: here, the statistical uncertainty associated with measurement in F14C becomes more of a problem. Additional details on the calibration process are developed and explained in Bronk Ramsey (2008).

Improving Procedures
Extracting original material
The first stage in the dating method is usually to take a sample, ideally of a single organism (“single-entity” dating, Ashmore 1999). The goal is to determine when the carbon in that organism was isolated from the atmosphere or the aquatic environment. In other cases, a mixture of materials may be dated, as in the case of bulk peat or coral, where a whole community of organisms is sampled together. There the assumption is that the community members all lived and died at the same time. In other cases the researcher takes samples of inorganic material such as stalactites and stalagmites, which have directly assimilated carbon from the environment at their time of formation in the form of “inorganic” carbon rather than living or organic carbon (Bronk Ramsey 2008).

A review of the revised edition of Libby’s book, Radiocarbon Dating (Simpson 1955) underscored the importance of context, and ensuring that samples were carefully collected, labeled and conserved prior to testing. The importance of this point remains today; selection of samples from an archaeological context requires professional archaeological expertise to ensure the context is preserved. The traditional practices of archaeology, including careful field notes, are important in maintaining accuracy in the application of the tool of radiocarbon dating. This parallels the challenges of modern forensics, where the smallest level of contamination at a crime scene, even in the most innocuous way, could lead to completely incorrect avenues of investigation, and false conclusions.

The first stages of the radiocarbon dating methodology, once a sample is received, are essentially an extension of this basic archaeological approach; the researcher must essentially ‘excavate’ the sample to recover original carbon-containing components that can be related back to the original organism(s) and, in doing so, must try to gather as much contextual information as possible about the sample which might be useful in interpreting any radiocarbon measurements made. Just as every site is different, so every radiocarbon sample is different in terms of the degree of preservation and the range of contaminants present. Therefore, although standardized methods can be used, this does not guarantee that all samples will behave in the same way.

First the sample is cleaned and inspected. For example, if the sample came from the ground, there may be plant roots tangled up with the sample, and these must be carefully removed. In the museum setting there may also be other visible signs of contamination, such as the use of glues or preservatives. This stage of the pre-treatment is a simple extension of what was started in the field, the aim being to separate the sample from its surrounding materials.

-Myself, based on research and reading done mostly for fun. I love anthropology, archaeology.. I could go on I guess, or just say all of science, the totality of the concept, learning, discovery, reexamination and further discovery... a process of logical steps.

C. (Christopher) Bronk-Ramsey is a pretty great source to go to, having developed many new techniques in dating, working on accuracy and precision, and also maintains a very powerful piece of machinery and so works with a lot of very interesting samples.
I would like to see an ffp something about cbronkramsey, for now here's the the rest of the pages of my poem about radio carbon dating, with sources...
(it's too bad I can't make sub scrip and other formatting, that would make it look more like it usually does.
*********************************

Perspectives on Radiocarbon Dating as an Archaeological Tool
May 2009

Summary

This paper reviews radiocarbon dating as a tool in Archaeology, tracing the history and origins of the concept that builds on related geological principles of stratification and seriation.  It outlines the scientific basis of radiocarbon dating and the nature of assumptions and inferences that are made; refinement of the technique in terms of adjustments and sources of error; and finally some conclusions about the usefulness and future of radiocarbon dating methods as applied to questions in Archaeology and Anthropology.

History and origins of radiocarbon dating

A recent article by Bronk Ramsey (2008) provided a particularly valuable starting point for this review, along with earlier review papers by Taylor (1996) and Mellars (2006). In his retrospective on radiocarbon dating Bronk Ramsey emphasized the several “revolutions” that have taken place over the past 60 years since the technique was first developed (by Libby et al. 1949, earning Libby, who was also associated with the Atomic Energy Commission, the Nobel prize for Chemistry in 1960). Bronk Ramsey (2008), coming from the perspective of specialization in the chemical pretreatment and analysis of radiocarbon samples, pointed out the importance of understanding the “life cycle” of radiocarbon, if one is to refine the resolution of dating, and emphasized the importance of an interdisciplinary approach in order to understand the roles of physical and biological processes in generating the information from which inferences may be drawn.

An interesting general introduction to Archaeology is provided in the compiled lectures that became In Pursuit of the Past, Binford (1983, with a new edition in 2002). Binford pointed out the need for archaeologists to be continuously self-critical as they work towards a balance between theory and practice. He also emphasized the fact that it is a field “wholly dependent upon inference to the past from things found in the contemporary world” and pointed out that this is fundamentally different from the approach of most fields where the past is seen as the period that helps us understand the present and predict the future!  The basic starting point and assumption was that things in the past worked much as they do in the present; this generates some debate as we discover that several aspects of the physical world have been changing as a result of both anthropogenic and natural changes in the physical environment (such as fluctuations in the production of ¹⁴Carbon); this will be discussed below.

There is obvious value to making several independent estimates of the age of an artifact or biological material, and while the idea of location and relative dating of material remains very important in Archaeology, today archaeologists can, and must, use several different techniques to determine the age of a particular artifact, object, feature or eco-fact within a site.  Geological stratigraphy is a relative dating method, in that it indicates the relative age of artifacts or site, as compared to others, but does not produce precise dates. Absolute dating methods that produce specific chronological dates for objects and occupations were not available to archaeology until the mid-20th century with Libby’s discoveries; taken together there is great value to the combination of these two categories of chronometric techniques; relative and absolute dating.

Studies of both the absolute and relative age of archaeological materials are essential to improving our understanding of the past. For example, Mellars (2006) pointed out that two recent developments in radiocarbon dating had shown that humans colonized Europe more rapidly than had previously been thought, and that they coexisted with Neanderthals for a shorter time than had been thought.

One of the advances that Mellars cited is the improvement of methods for pre-treating bone samples developed by Bronk Ramsey et al. (2004b).  This has allowed much better purification of bone collagen, reducing more recent carbon-containing contamination, and thereby increasing the precision (and measured age) of materials in Europe. The other major breakthrough according to Mellars (2006) is the improved understanding of fluctuations in the ¹⁴Carbon content of the Earth’s atmosphere over the past 50,000 years. This valuable perspective was shown based on a long sequence of 280 stratified radiocarbon samples from deep-sea sediments in the Cariaco Basin, near Venezuela, that were cross-referenced to isotopic Oxygen (¹⁸O/¹⁶O) ratios from Greenland ice core samples (Hugen et al. 2004).

Stratigraphic principles and relative time

To understand the application of stratigraphy to archaeology, we should review the underlying geological principles of deposition (e.g. see Historical Geology by Wicander and Monroe 2007, and notes from Geology 3110, Earth and Life Through Time). In large part Earth's geology is made up of successive layers of different rock types, deposited one on top of another. Usually these are sedimentary rocks (derived from what were formerly sediments washed down into marine or freshwater basins and deposited on the lake or sea bottom), and extrusive igneous rocks (e.g., lavas, volcanic ash, and other formerly molten rocks extruded onto the Earth's surface). The layers of rock are "strata", and their study is "stratigraphy". Stratigraphy is based on geometry, empirical observation of the way these rocks are deposited today, and gravity. These ideas were first formally proposed by the Dane, Nicolaus Steno (known in Danish as Niels Steensen), in 1669. Charles Lyell's Principles of Geology, published in 1830-32, outlined principles that have held up to the present The principle of superposition: in a vertical sequence of sedimentary or volcanic rocks, a higher rock unit is younger than a lower one. "Down" is older, "up" is younger.

1. The principle of original horizontality: rock layers were (at least originally) deposited close to horizontal.

1. The principle of original lateral extension: a rock unit continues laterally unless there is a structure or change to prevent its extension.

1. The principle of cross-cutting relationships: a structure that cuts another is younger than the structure that is cut.

1. The principle of inclusion: a structure that is included in another is older than the including structure.

1. The principle of "uniformitarianism": processes operating in the past were constrained by the same "laws of physics" as operate today.

There are exceptions to these general principles e.g., in caves, the cave contents are younger than both the bedrock below the cave and the roof above. But the "principle of cross-cutting relationships", in the case of the contact between the cave infill and the surrounding rock shows the true relative age relationships, as will the "principle of inclusion" if fragments of the surrounding rock are found within the infill. Cave deposits are usually quite distinctive in other ways (e.g. they have spelothems like stalactites and stalagmites), so they would not readily be confused with a successional sequence of rock units. While caves are not particularly common geological forms, they are often the places where early human activities took place, so these exceptions and concerns may be more relevant in archaeology.

The simplest situation for a geologist is a "layer cake" succession of sedimentary or extrusive igneous rock units arranged in nearly horizontal layers. In such a situation, the "principle of superposition" is easily applied, and the strata towards the bottom are older, those towards the top are younger; this principle has been widely used and applied in Archaeology.

Scientific basis of ¹⁴Carbon dating

In 1949, Willard Libby and his colleagues at the University of Chicago first developed the “radiocarbon” dating (RCD) method. Fagan and DeCorse (2005) describe this dating tool as being a direct byproduct of the research and development of the Atomic bomb during World War II. Radiocarbon dating can be used to date wood, bone and other organic (carbon-containing) materials up to 40,000 years old. Based on experiments in his laboratory, Libby found that the radioisotope ¹⁴Carbon decayed at a rate that, projected out, would cause half of its radioactive atoms to have decayed to the ¹²C form in 5568 years. Hence the term ‘half-life’ was given to radioactive substances. A more recent estimate of the half-life of radiocarbon is given by Bronk Ramsey (2008) who gives it as 5730 years. Because this is a relatively short period of time, we know there is no “primordial” carbon, so radiocarbon dynamics are driven by the equilibrium between various reservoirs, along with its main mode of production in the upper atmosphere, and its radioactive decay.

A fundamental assumption about radiocarbon dynamics is that its patterns of production, movement, and dispersal through environments have not changed much over time. Also, that radiocarbon present in the remains of an organism was acquired only during their life, and because of the ongoing turnover of living tissues, it was inferred to have been assimilated during the last portion of their life prior to being deposited and/or preserved in some way. However, research indicates that some tissues such as shell or tooth enamel are not subject to turnover (Spalding et al. 2005), and would have been incorporated at the time of formation, allowing them to be used for detailed aging of long lived organisms. The method was first tested on objects with known dates and an established, relatively recent historical age (Egyptian mummies). It would be true to say that this development completely revolutionized the study of archaeology, and the technique was soon being applied to dating sites that had been occupied many thousands of years earlier.

Cosmic radiation produces neutrons that enter Earth’s atmosphere and react with Nitrogen (which in the normal isotopic state contains 7 protons and 7 neutrons in the nucleus for a total atomic mass of 14, as the 7 electrons are very light in mass). This reaction produces ¹⁴Carbon, an isotope of Carbon with six protons and eight neutrons, rather than the usual six, in the atomic nucleus, for a total atomic mass of 14. With these additional neutrons, the nucleus becomes unstable, and undergoes a gradual radioactive decay process. (Based on course notes from Chemistry 2610: Northern Environmental Chemistry).

Three methods of carbon-14 dating are used today: “gas proportional counting” (or GPC), “liquid scintillation counting” (or LSC), and “accelerator mass spectrometry” (or AMS) (see Bronk Ramsey 2008, p258). These methods are an improvement over Libby’s original method, which required larger samples of at least 1g, and involved counting individual radioactive decay events. The new methods enable dating to be done with much smaller samples. The GPC and LSC methods require a sample of at least 100mg. With AMS, samples can be as small as 1mg; 1/1000 of the sample size required with Libby’s original method. Obviously there is a great benefit to requiring a smaller (destructive) sample from an old or precious specimen.

In GPC, a sample is reduced to carbon dioxide or methane gas. A proportional counter is filled with this gas, and the electrical discharge from the decay of the ¹⁴C is counted electronically. In LSC, the sample is converted to benzene. This is mixed with certain organic chemicals and placed in a clear container. Whenever a ¹⁴C atom decays, the liquid emits a pulse of light. Sensitive photo multiplier tubes are placed near the container. These tubes can count the pulses of light. Since the decay of a radioactive atom is a random event, it takes a number of days to get a count accurate enough to find the age of the sample. Both of these methods measure the radioactivity of the sample.

In AMS dating, individual ¹⁴C atoms are counted through the use of an accelerator mass spectrometer. Ionized carbon atoms are first pulled, as a beam towards the accelerator. A beam-bending magnet segregates the isotopes of Carbon because lighter charged particles bend more than heavier ones; a filter sorts out any other molecules that have atomic mass 14, and then the beam is focused to land on a very sensitive detector that counts the number of remaining ions. If we know the total initial number of ions in the sample, the ratio of ¹⁴C:¹²C can be calculated (see Linick et al. 1989).

There is of course a challenge when looking at archaeological materials that are older than 50,000 years. Here it is necessary to switch to another radioisotopic method, Potassium-Argon dating. ⁴⁰Potassium (⁴⁰K) decays to ⁴⁰Argon (⁴⁰Ar) which is an inert gas, and to Calcium. Potassium is present in most geological materials, making potassium-argon dating very useful where there are contemporaneous remains. Potassium makes up about 1/40 of the earth’s crust, and about 1/10,000 of the potassium is ⁴⁰K.

Other radioactive isotopes are also useful for older materials: Uranium decays to Lead by a complex series of steps, and Rubidium decays to Strontium. Thus we can use K-Ar dating, U-Pb dating, and Rb-Sr dating for dating materials of various ages. Argon laser dating is a more recent method developed to measure the relative amounts of ⁴⁰Ar/³⁹Ar in crystalline feldspar from volcanic ash (tephra), indicating how much time has elapsed since the crystals formed. This technique is particularly useful in dating old materials such as pumice samples co-occurring with the remains from early hominids.  This was done with the Homo erectus samples from Modjokerto (in Java). The results suggested that samples previously estimated as being 1 million years old actually dated back as much as 1.8 million years (Jacob 1973; Jacob and Curtis 1971), calling for a re-examination of the likely pathway of early hominid migration out of Africa.

 

Anthropological/archaeological applications, sources of error and other considerations

There have been concerns over the assumption that there is a constant rate of generation of ¹⁴Carbon, particularly since the era of atmospheric nuclear bomb tests.  These nearly doubled the abundance of radiocarbon in the atmosphere in the mid-1960s. Since then the concentration has been falling, and will in a few years (probably within the next decade) fall to the pre-bomb values (Bronk Ramsey 2008). Interestingly the elevated ¹⁴C in marine systems has been used to verify age estimates of long-lived fish based on analysis of fish otoliths (ear bones), which have annual growth rings similar to those in trees (Kalish 1995).

Other sources of variation in ¹⁴C production would be variations in the cosmic ray flux, which in turn is affected by changes in the Earth’s magnetic field. There have been several attempts to measure the rate of production of radiocarbon, leading to the conclusion that a rate of 2-3 ¹⁴C atoms cm^-2 s^-1 (atoms per square centimeter per second) is reasonable, but Bronk Ramsey et al. (2007) have explored the rate of production of radiocarbon in the atmosphere, and Mak et al. (1999) have done the same at ground level, and there are very different values in these two locations. Bronk Ramsey (2008) points out however that we don’t need to know the rate of production to carry out radiocarbon dating; we need to be aware that the rate will have varied on a range of timescales, and for dating within a century or so, we only need to know the concentration in the atmosphere.

Materials can change over time; indeed even during the life of an organism, its living tissues are constantly turning over. Once an organism dies, breakdown occurs rapidly and usually little remains after a few years. However, in some conditions (e.g. waterlogged deposits and very dry conditions), there is better preservation. This is of course exceptional, so groupings of organisms in a site will not necessarily represent their original assemblages (e.g., in terms of biodiversity or co-occurrences in life). Exactly what survives in the ground and how it does so, is a complex topic. For example, in acidic peat deposits there may be virtually no mineral components remaining but organic preservation may be very good (e.g., the “bog people” preserved in Denmark and other areas in Northern Europe). In hot dry conditions the reverse is likely to be true, with very good mineral preservation and poor preservation of proteins (Hedges and van Klinken 1992). Ultimately, remains of this sort become fossilized, with full replacement of the original material by minerals from the surrounding matrix. Even before this happens, the mineral components of bone and shell often exchange carbon with dissolved carbonate, and so may not retain the original radiocarbon ratio signal (Bronk Ramsey 2008). It is worth noting that this generalization does not match with the findings cited earlier by Spalding et al. (2005).

Additional factors that can affect the accuracy of radiocarbon dating include contamination of the original sample with more recent materials, particularly following acid/base/acid pretreatment (Bronk Ramsey et al. 2004b). For example, bone, as a complex sample material, is routinely used in radiocarbon dating. Prior to carrying out AMS (as first developed by Linick et al. 1989) pre-treatment of the material is important, and that has been an area of ongoing method refinement with many improvements occurring through the work of Bronk Ramsey and his collaborators. According to Bronk Ramsey et al. (2004b), the most effective method of pretreatment for dating many samples has been a simple demineralization, which is effective at removing the most ubiquitous contaminants. An acid/base/acid treatment also removes humic contaminants which can be a significant source of error in many organic-rich contexts. However, these treatments leave behind many organic molecules from the soil and degraded protein fragments, making the sample susceptible to contamination (and under-aging).

 

Theoretical challenges with ¹⁴C dating

Bronk Ramsey (2008) pointed out a number of challenges that may affect the accuracy of the radiocarbon dating methods in use today.  Note that these concerns are issues that will affect the accuracy, rather than the precision of the method; there is no doubt that the adoption of AMS has greatly increased the precision of measurements made. However, for radiocarbon dating to be reliable a number of assumptions are made.

Firstly, Libby assumed that ¹⁴C decays at a constant rate. However, experimental evidence indicates that ¹⁴C decay is slowing down and that millennia ago it likely decayed much faster than today.  It is not clear why this is so.  Secondly, the theory behind ¹⁴C dating requires that there is the same rate of cosmic production of radioactive isotopes throughout time. The industrial revolution released hundreds of thousands of tons of carbon gases into the atmosphere, increasing the relative proportion of ¹²C.  Furthermore, atmospheric testing of atomic weapons increased neutron levels, raising¹⁴C, so there does not appear to be a constant background (atmospheric) ratio. Thirdly, the environment in which the artifact lies significantly affects the rate of decay. For example, ¹⁴C leaches faster from organic material saturated in water, especially saltwater.  Fourthly, for ¹⁴C to be measured accurately the archaeological artifact must have been protected from contamination. Organic matter, being porous, can easily be contaminated by organic carbon in groundwater. This increases the ¹²C content and affects the carbon isotope ratio (Bronk Ramsey 2008).

Variations in production rate of ¹⁴C can also be attributed to changes in the stream of cosmic rays hitting the Solar System, and due to variations in the Earth’s magnetic field that shields the Earth from the charged particles. On the timescales involved in radiocarbon dating, we would expect the overall cosmic ray flux to the solar system to remain fairly constant, although there may be individual events (such as supernovae) that do occasionally contribute significantly (Damon et al. 1995). This screening effect is in turn affected by solar activity and by the primary strength and direction of the magnetic field itself, and these can lead to very significant variations in radiocarbon production rates. This reaction takes place largely in the upper atmosphere, where thermal neutrons, resulting from a cascade of reactions from cosmic rays, react with the nitrogen atoms in air. Some production is also possible even at ground level, but the rates are about two orders of magnitude lower (Mak et al. 1999), at about 1 x 10^-4 atoms g^-1 s^-1 (atoms per gram per second) or virtually statistically insignificant.

In theory, it could undermine the interpretation of radiocarbon data, if radiocarbon is being formed in situ at ground level. The processes involved are very complex because of moderation of neutrons and attenuation of cosmic rays, and the fact that other production reactions involving oxygen (and therefore oxidation levels) are also possible. However, Bronk Ramsey (2008) argued that in situproduction of ¹⁴C should not normally be a significant issue in dating unless there is exposure to high neutron doses from other sources.

Comparisons with records of past radiocarbon concentration

If we can establish the compartment in the carbon cycle from which the carbon in a sample was taken, we are able to modify our expectation of starting ratios of Carbon isotopes, and make our measurement in the light of knowledge of the past environment and the decay rate of radiocarbon. Otherwise we can make “reasonable assumptions” (e.g., that the past radiocarbon ratio was as it was in 1950), and use our estimates of the half-life of radiocarbon to estimate the age of the sample. With such an estimate it is very difficult to give statistical confidence limits.

Ideally, we should have material of known age whose carbon is drawn from the same pool as our sample. This is true for the atmosphere in the period where we have wood that has been dated dendrochronologically (using tree rings) as well as with ¹⁴C (Reimer et al. 2004). Also, since 1950, we have data on direct atmospheric measurements (Hua and Barbetti 2004). In these cases all we need to do is to compare the radiocarbon measurement for our sample with the reference measurements. In practice, rather than comparing directly to the individual measurements, we put together a radiocarbon calibration curve that gives our best estimate (with quantified uncertainties) for the measurement that we would get for a sample of any age within the range of the data (Buck and Blackwell 2004). In his review, Mellars (2006) has cited improvements in the calibration of radiocarbon time as the most important recent breakthrough, and indeed it provided improvements that are particularly useful to archaeology. The revised calibration showed that there had been a rapid change in radiocarbon ages over the period 40,000-35,000 radiocarbon years ago. This was due to rapid changes in ¹⁴C content of the atmosphere over that period. The net result is that dates that covered an apparent 5,000 years actually only covered 3,000 years. Fortunately what this does is to give us greater dating precision for a very important time period in human evolution and dispersal.

Such radiocarbon calibration curves are typically expressed in terms of radiocarbon years except for the period after 1950, but it is better both conceptually and mathematically to consider them as a “fractionation-corrected” isotope ratio or “F¹⁴C”. In terms of the algorithms for calibration, this makes almost no difference until the measurements approach background levels: here, the statistical uncertainty associated with measurement in F¹⁴C becomes more of a problem. Additional details on the calibration process are developed and explained in Bronk Ramsey (2008).

Improving Procedures 

Extracting original material

The first stage in the dating method is usually to take a sample, ideally of a single organism (“single-entity” dating, Ashmore 1999). The goal is to determine when the carbon in that organism was isolated from the atmosphere or the aquatic environment. In other cases, a mixture of materials may be dated, as in the case of bulk peat or coral, where a whole community of organisms is sampled together. There the assumption is that the community members all lived and died at the same time. In other cases the researcher takes samples of inorganic material such as stalactites and stalagmites, which have directly assimilated carbon from the environment at their time of formation in the form of “inorganic” carbon rather than living or organic carbon (Bronk Ramsey 2008).

A review of the revised edition of Libby’s book, Radiocarbon Dating (Simpson 1955) underscored the importance of context, and ensuring that samples were carefully collected, labeled and conserved prior to testing. The importance of this point remains today; selection of samples from an archaeological context requires professional archaeological expertise to ensure the context is preserved. The traditional practices of archaeology, including careful field notes, are important in maintaining accuracy in the application of the tool of radiocarbon dating.  This parallels the challenges of modern forensics, where the smallest level of contamination at a crime scene, even in the most innocuous way, could lead to completely incorrect avenues of investigation, and false conclusions.

The first stages of the radiocarbon dating methodology, once a sample is received, are essentially an extension of this basic archaeological approach; the researcher must essentially ‘excavate’ the sample to recover original carbon-containing components that can be related back to the original organism(s) and, in doing so, must try to gather as much contextual information as possible about the sample which might be useful in interpreting any radiocarbon measurements made. Just as every site is different, so every radiocarbon sample is different in terms of the degree of preservation and the range of contaminants present. Therefore, although standardized methods can be used, this does not guarantee that all samples will behave in the same way.

First the sample is cleaned and inspected. For example, if the sample came from the ground, there may be plant roots tangled up with the sample, and these must be carefully removed.  In the museum setting there may also be other visible signs of contamination, such as the use of glues or preservatives. This stage of the pre-treatment is a simple extension of what was started in the field, the aim being to separate the sample from its surrounding materials.

 

Sample treatment

Next is purification of the original components of the sample, by chemical pre-treatment of some sort, continuing the process of reducing the contaminants present in the sample, and preventing addition of modern contaminants. Most, though not all, environmental contaminants are comparable in age to the samples, or younger: such contamination is generally more of a problem when old samples are being studied. Laboratory contaminants are usually either free from radiocarbon (of geological origin) or are modern; these can greatly skew the apparent results.

Tolerance of contamination differs for samples of different ages; for high-precision dating, Bronk Ramsey (2008) reports that where effects of the order of 10 years are important for recent samples, modern and geological age contaminants need to be kept below about 0.1%, or about 10 µg C, in a typical AMS sample (Bronk Ramsey et al. 2004a).  The method is less sensitive to contaminants that are roughly the same age as the sample, so in this case contaminant levels of about 1% are acceptable.  For the dating of very old material, we need to ensure that modern contamination remains below 0.1%, and that contaminants that are roughly half the age of the sample will not become too important until they get above about 1%. In such cases, contaminants that are similar in age or much older are not an issue.

For many sample types, Bronk Ramsey (2008) details fairly simple pre-treatment methods are sufficient for recovering original material from samples. For organic samples, these methods are usually variations on the acid–base–acid (ABA) methods in which an initial acid treatment removes carbonate precipitated on to the samples from groundwater, the base (or alkali) stage removes humic acid contaminants from the sediment and a final acid stage removes any carbonate dissolved from the air during the pre-treatment. For inorganic samples, acid is often used on its own, after an initial etch, to extract CO₂ from the aragonite or calcite that forms the sample. The reason why these methods often work well is that the samples retain original material in large molecules (cellulose, or allotropes of carbon or calcite/aragonite crystals) in reasonably high purity, with contaminants that are only loosely bound or are sufficiently close in age not to compromise the dating accuracy.

There have been attempts to use the carbonate portion of bones for radiocarbon dating by releasing CO₂ with hydrochloric acid. However, data can be misleading as ground water contains atmospheric carbon dioxide of modern ¹⁴C age. This carbonate can be exchanged with radioactively dead carbonate in the soil (e.g. limestone). Therefore, ground-water carbonate could add anywhere from 0 to 5730 years to a radiocarbon age. As a result, bones immersed in modern carbonate-containing water could be dated as being too young and bones in “radioactively dead” water as being too old. Since older bones have a much less preserved structure than young bones, the error will be most pronounced in older specimens, as they would have more opportunities for Carbon exchange.

Initially, radiocarbon dating of archeological bone samples was mostly based on the dating of associated charcoal, and sometimes the calcium carbonate contents in bones but this practice was questioned by Libby’s group, who instead extracted organic carbon from these materials (e.g., Berger et al. 1964). They showed errors when dates were based on charcoal analysis, and that the carbonate in calcium carbonate could be replaced by ground-water carbonate of varying (and younger) age. Today it is routine to date bones directly from their content of organic carbon or collagen (Nelson 1991). The advantage of this method is that there is no known natural mechanism that would alter collagen to give a false age. Generally, dry modern bone is composed of approximately 50 percent calcium phosphate, 10 percent calcium carbonate, 25 percent collagen, and 5 to 10 percent bone fat, and the remainder is made up mainly of muco-polysaccharides, calcium fluoride, magnesium phosphate, sodium salts, iron and manganese. Collagen is a protein with characteristic ratios of particular types of amino acids, it is resilient, and it is specifically hydrolyzed by the enzyme collagenase. Its thin fibrils (0.3 to 0.5A thick) are found throughout bone; turnover of these molecules is very slow.

Dating of bones from their collagen, which does not suffer from exchange processes, is now routine. However, the collagen content of bone decreases with age to such low concentrations that isolation of sufficient collagen for radiocarbon dating becomes difficult with the oldest bones. According to Oakley (1963),

The oldest specimen that has been dated in this way had a collagen content of about 0.16 percent. It was about 9000 years old (specimen no. UCLA-630). Unfortunately collagen does not decrease uniformly with age for samples from around the world. For example, a 4000 year-old bone from Santa Rosa Island, California, (specimen no. UCLA-140), buried in dry, permeable soil, had a collagen content of about 15 percent whereas a 3300-year-old bone buried in moist English conditions had only 10 percent.

However, when bones of different ages are found in the same general locality, they can be relatively dated, depending on their collagen content. Cook and Heizer (1953, cited in Berger et al. 1964) were able to arrive at reasonably good absolute dates for bones derived from their collagen content for the general area of the southwestern United States. Bones of the same age may have different collagen contents depending on their matrix and environmental conditions.

Measurement of isotopic ratios

The aim of the measurement stage in the technique is to measure the isotope ratio accurately and with as much precision as possible. The two main methods employed are decay counting methods (using liquid scintillation and gas proportional counters) and accelerator mass spectrometry (AMS), where the radiocarbon atoms are detected directly. The reliability of the measurement depends on three related considerations: detection efficiency, instrument precision and sample purity (which was addressed above).

In terms of detection efficiency, AMS methods that count the radioactive, and therefore heavier, atoms directly are much more efficient than counting methods that only detect those individual atoms that decay. Typical total AMS detection efficiencies are about 1%, and at best about 5% with ion source efficiencies of 10% and stripper efficiencies of 50%. In theory this means that samples can be much smaller, around 1mg.

Instrument stability has greatly improved in the past ten years, so factors such as counting statistics or uncertainties in sample purity are becoming the limiting factors for improvements (Steier and Rom 2000; Bronk Ramsey et al. 2004a). One remaining aspect is that there is usually a limit to how long a single target can be measured with high stability, so very high precision measurements usually require multiple targets. Counting instruments (GPC and LSC) which are intrinsically simpler, can still achieve better overall precision if it is possible to use a larger sample, and take more time (Stuiver et al. 1998; Hogg et al. 2002).

Sample purity is another area where AMS is not necessarily better than the older counting

methods. The advantage of AMS is that a smaller sample size is needed and so in some

instances it may be possible to use a pretreatment method (such as ABOX for charcoal, or

ultrafiltration for bone) that cannot be applied to a large sample. However, in many cases, if the sample is large enough for conventional measurement, there is a suitable method for thorough pretreatment (e.g., for well-preserved wood or calcite) and the larger sample size helps reduce laboratory contamination. With AMS, even after the purification of the sample, it is necessary to combust the sample to CO₂ and then, usually, to reduce it to graphite; these two stages can introduce some carbon (typically about 1µg C) and uncertainties in this value, and the composition of this carbon limits the precision of the measurement for very small samples. That’s why, in practice, > 100µg C is often needed for good precision. Improvements are always being made in the measurement of small samples (Hua and Barbetti 2004; Santos et al. 2007). Another approach is to bypass the production of gas and use the CO₂ directly in the ion source (Bronk Ramsey and Hedges 1997). This method is good for small samples, although the overall efficiencies quoted are similar to those for graphite.

Online Gas Chromatography (GC) and High Performance Liquid Chromatography (HPLC) applications are also possible with such sources, with much lower combustion backgrounds (Bronk Ramsey et al. 2004a), but as the quantities of carbon in each peak are typically of the order of 1µg C or less, such methods cannot yield precision suitable for dating, and are unlikely ever to do so unless many repeat analyses are made.

The most significant development is undoubtedly the introduction of AMS for the direct detection of radiocarbon, allowing a whole range of smaller samples to be measured. New smaller accelerators (Suter et al. 2000) reduce the capital cost of setting up such facilities, but have not so far increased measurement precision.

The ability to analyze small samples is just one of the great strengths of AMS. Exploration of early agriculture in the Near East and Mesoamerica was greatly facilitated by AMS-based analysis that can use very small samples to analyze plant remains. Other tissues that are now available for analysis by these methods include New World Paleo-Indian human skeletal remains and European Upper Paleolithic and Mesolithic material (Taylor, 1996). 

The measurement stage of the process of radiocarbon analysis is no longer the limiting factor for precision and accuracy, except for the very smallest samples. It is useful that, in general, the measurements made decades ago are still valid within their quoted error limits, and in the light of better knowledge of the calibration curves. Any problems that occur today in radiocarbon dating most often arise either in the pretreatment stage of the process or in the interpretation of the radiocarbon measurement.

Conclusions: have we reached the limits to development of radiocarbon dating?

In his introductory remarks, Bronk Ramsey (2008) expressed some dismay that there had been so many “revolutions”, citing works by Renfrew (1973), Atkinson (1975), Linick et al. (1989), Taylor (1996), and Mellars (2006). He seemed to view the sheer number of these shifting views as reflecting poorly on the application of science to the arts. However the idea of a series of revolutions has been part of the thinking in this area for some time; Colin Renfrew, the person who organized the assembly of Binford’s (1983) book, first discussed improvements in ¹⁴C measurement in terms of revolutions (e.g. Renfrew 1973). While Bronk Ramsey may feel the word “revolution” is excessive to describe what are simply refinements of a methodology and approach to sample preparation, I would suggest that the ongoing improvement of methods and procedures is a healthy practice that reflects the increasing precision of techniques and the opportunities offered by new and better instrumentation, with better limits of detection allowing more precision and the use of ever smaller samples of material that have been prepared under conditions that limit opportunities for contamination.  Of course the question of increasing accuracy depends on the interpretation of that information and ever-better understanding of background variations in the composition of the atmosphere, and other issues that affect what is measured.  This requires building in the scientific framework of “controls” within an “experimental” context.
It is interesting that in his 2006 review, Mellars emphasized the revolutions in purification of samples (a strength of Bronk Ramsay’s research), and our better understanding of atmospheric changes, whereas Taylor’s 1996 review (which interestingly is not cited by Mellars), suggests the two big revolutions in his view have been in terms of understanding and calibrating atmospheric variations in¹⁴C against calendar time, and the introduction of AMS techniques.

Bronk Ramsey (2008) has pointed out that the measurement of radiocarbon is inherently difficult, because it occurs in very low concentrations, with the ¹⁴C/¹²C ratio being in the range 10^-12–10^-15. This sets a critical limit on the precision of a radiocarbon date and dictates how much material would be needed to get a reasonable estimate. Even assuming 100% detection, if there are only “n” radiocarbon atoms present, then the relative precision of any isotope ratio measurement is limited to 1/vn. As a result, to achieve a precision of 25 years (0.3%), we would need at least 105 radioactive atoms present, requiring 2µg C for a modern sample, or about 10µg C for a sample that is 12,000 years old. In his view, no technical development can overcome this fundamental limitation.

It is apparent now that human origins stretch far beyond the 50,000 year dating range of ¹⁴C; clearly additional methods will be needed to explore chronometry of the earlier stages of human evolution. For example Mishra (1995) shows that ¹⁴C and Th/U dating do not provide the necessary information to date Acheulian remains in India, but that K/Ar analysis of a tephra (volcanic ash) layer associated with an early Acheulian “industry” indicates an age of 670,000 years. These estimates were corroborated by independent data on paleomagnetic stratigraphy Rendell and Dennell (1985) and suggest that humans were in the Indian subcontinent in the Pleistocene, earlier than previously thought, but this view matches with the chronology of stone age cultures in other parts of the “old world”.

Some more subtle issues may be addressed in the future. For example, plants have several distinct mechanisms for incorporating CO₂ in sugars.  Some, (C₃ plants) fix atmospheric CO₂ into a 3-Carbon sugar.  In these plants the isotope separation effect is more pronounced.  In C₄ plants CO₂ is incorporated into a 4-Carbon sugar, where the non-radioactive mass isotope, the heavier ¹³C is less depleted, and in Crassulacean Acid Metabolism (CAM) plants, the effect is similar but less pronounced than with C₄ plants. The different isotope ratios for the two kinds of plants propagate through the food chain, thus it is possible to determine if the principal diet of a human or an animal consisted primarily of C₃ plants (rice, wheat, soybeans, potatoes) or C₄ plants (corn, or corn-fed beef) by carrying out isotope analysis of their flesh and bone collagen. Similarly, marine fish contain more ¹³C than freshwater fish, with values approximating the C₄ and C₃ plants respectively. This would allow marine and freshwater fish diets to be distinguished (Maberly et al. 1992).

 

In closing, one aspect of this review that I have personally found most interesting is the obvious importance of an interdisciplinary approach. To really understand the value of this chronometric method, it is necessary to understand principles of nuclear physics, geology, biology of photosynthesis and trophic ecology, preservation chemistry, and analytical chemistry, among other areas. Paramount however is the importance of retaining the basic principles of archaeology from the point of discovery and collection, as emphasized by many of the authors cited in this report. Clearly, major evolution of methodologies has been occurring over the past 60 years, and continues today.

I don’t believe that the ongoing revision of methods reflects negatively on the discipline as suggested by Bronk Ramsey at the beginning of his review. Instead it is very valuable to explore where increased technical precision must be matched by caution about accuracy of the sample gathering, storage and preparation for analysis as well as background assumptions built into the original concept of ¹⁴C dating.  The field of ¹⁴C dating provides a useful tool, but cross-validation with different dating methods, including traditional relative dating approaches, allows us to be more confident about the results. It is appropriate to remain cautious about the context of interpretation of results, as we seek to understand our origins, our past, and our development to the present day.

 

References

Ashmore, P. 1999, Single entity dating, Mémoires de la Société préhistorique française, 26: 65–71.

Atkinson, R. 1975. British prehistory and the radiocarbon revolution, Antiquity, 49(195), 173–7.

Berger, R, Horney, AG and Libby, WF. 1964. Radiocarbon Dating of Bone and Shell from their Organic Components. Science Volume 144, No 3621: 999-1001.

Binford, LR 1983, 2002. In Pursuit of the Past: Decoding the Archaeological Record. Thames & Hudson Pub. NY, NY.

Bronk Ramsey, C. 2008. University of Oxford, 2008, Archaeometry 50 (2): 249–275

Bronk Ramsey, C, Brenninkmeijer, CAM, Jöckel, P, Kjeldsen, H, and Masarik, J. 2007. Direct measurement of the radiocarbon production at altitude, Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 259(1), 558–564.

Bronk Ramsey, C, and Hedges, R. E. M., 1997, Hybrid ion sources: radiocarbon measurements from microgram to milligram, Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 123(1–4): 539–545.

Bronk Ramsey, C, Higham, T, and Leach, P. 2004a. Towards high-precision AMS: progress and limitations, Radiocarbon, 46(1): 17–24.

Bronk Ramsey, CB,  Higham, T, Bowles, A and Hedges, REM. 2004b. Improvements to the Pretreatment of Bone at Oxford.   Radiocarbon 46 (1):155–163

Buck, CE, and Blackwell, PG. 2004. Formal statistical models for estimating radiocarbon calibration curves, Radiocarbon, 46(3): 1093–1102.

Cook, SF, and Heizer, RF. 1953. Southwestern Journal of Anthropology 9: 231. Cited in Berger, R, AG Horney and WF Libby. 1964. Radiocarbon Dating of Bone and Shell from their Organic Components.Science Vol. 144, No 3621: 999-1001.

Damon, PE, Kaimei, D, Kocharov, GE, Mikheeva, IB, and Peristykh, AN. 1995. Radiocarbon production by the gamma-ray component of supernova explosions, Radiocarbon, 37(2), 599–604.

Fagan BM and DeCorse CR 2005. In the Beginning: An Introduction to Archaeology. 11^th Edition. Prentice-Hall. New Jersey, USA. 578 pp.

Hedges, REM, and van Klinken, GJ. 1992. A review of current approaches in the pretreatment of bone for radiocarbon dating by AMS, Radiocarbon, 34(3), 279–291.

Hogg, AG, McCormac, FG, Higham, TFG, Reimer, PJ, Baillie, MGL, and Palmer, JG. 2002. High precision radiocarbon measurements of contemporaneous tree ring dated wood from the British Isles and New Zealand: AD 1850–950, Radiocarbon, 44(3), 633–40.

Hugen, K, Lehman, S, Southon, J, Overpeck, J, Marchal, O, Herring, C, Turnbull, J. 2004. ¹⁴C activity and global carbon cycle changes over the past 50,000 years. Science 303: 202-207.

Hua, Q, and Barbetti, M. 2004. Review of tropospheric bomb C-14 data for carbon cycle modeling and age calibration purposes, Radiocarbon, 46(3), 1273–98.

Jacob T and GH Curtis. 1971. Preliminary Potassium- Argon dating of early man in Java. Contr. Univ. Calif. Archaeol. Rex. Facil., 12: 50.

Jacob, T. 1973. “Palaoanthropological discoveries in Indonesia with special reference to the finds of the last two decades.” Journal of Human Evolution 2:473-85.

Kalish, JM. 1995. Application of the Bomb Radiocarbon Chronometer to the Validation of Redfish Centroberyx affinis Age. Canadian Journal of Fisheries and Aquatic Sciences 52(7): 1399-1405.

Linick, TW, Damon, PE, Donahue, DJ, and Jull, AJT. 1989. Accelerator mass spectrometry: the new revolution in radiocarbon dating, Quaternary International, 1, 1– 6.

Libby, WF 1955. Radiocarbon Dating. Second Edition. University of Chicago press, Chicago 175pp.

Libby, WF, Anderson, EC, and Arnold, JR. 1949. Age determination by radiocarbon content: world-wide assay of natural radiocarbon, Science, 109(2827), 227–8.

 

Maberly, SC, Raven, JA, Johnston, AM. 1992. Discrimination between12C and13C by marine plants. Oecologia 91: 481

Mak, J, Brenninkmeijer, C, and Southon, J. 1999. Direct measurement of the production rate of C-14 near Earth’s surface, Geophysical Research Letters, 26(22): 3381–4.

Mellars, P. 2006. A new radiocarbon revolution and the dispersal of modern humans in Eurasia. Nature 439: 931-935.

Mishra, S. 1995. Chronology of the Indian Stone Age: the Impact of Recent Absolute and Relative Dating Attempts. Man and Environment XX (2): 11-16.

Nelson, DE. 1991. A new method for carbon isotopic analysis of protein, Science 251(4993): 552–4.

Oakley, KP. 1963. Science 140: 488 (Cited In Berger et al., 1964).

Renfrew, C. 1973. Before Civilization: the Radiocarbon Revolution and European Prehistory, Jonathan Cape, London.

Reimer, PJ, Baillie, MGL, Bard, E,  Bayliss, A, Beck, JW, Bertrand, CJH, Blackwell, PG, Buck, CE, Burr, GS, Cutler, KB, Damon, PE, Edwards, RL, Fairbanks, RG, Friedrich, M, Guilderson, TP, Hogg, AG, Hughen, KA, Kromer, B, McCormack, G, Manning, S, Bronk Ramsey, C, Reimer, RW, Remmele, S, Southon, JR, Stuiver, M, Talamo, S, Taylor, FW, van der Plicht, J, and Weyhenmeyer, CE. 2004. IntCal04 terrestrial radiocarbon age calibration, 0–26 cal kyr bp, Radiocarbon, 46(3), 1029–58.

Rendell, HM, and RW Dennell. 1985. Dated Lower Paleolithic Aretefacts from Northern Pakistan. Current Anthropology 26: 293.

Santos, GM, Southon, JR, Griffin, S, Beaupre, SR, and Druffel, ERM. 2007. Ultra small-mass AMS 14C sample preparation and analyses at KCCAMS/UCI Facility, Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 259(1): 293–302.

Simpson WK. 1955. Book Review of Radiocarbon Dating by WF Libby. American Journal of Archaeology Vol. 61(4): p387.

Spalding, KL, Buchholz, BA, Bergman, LE, Druid, H, Frisen, J. 2005. Forensics: age written in teeth by nuclear tests. Nature 437 (7057): 333-4.

Steier, P, and Rom, W. 2000. The use of Bayesian statistics for C-14 dates of chronologically ordered samples: a critical analysis, Radiocarbon, 42(2), 183–98.

Stuiver, M, Reimer, PJ, and Braziunas, TF. 1998. High-precision radiocarbon age calibration for terrestrial and marine samples, Radiocarbon, 40(3), 1127–51.

Suter, M, Jacob, SWA, and Synal, HA. 2000. Tandem AMS at sub-MeV energies—status and prospects, Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 172(1–4), 144–51.  (See also)

Taylor, RE., 1996, Radiocarbon dating: the continuing revolution, Evolutionary Anthropology, 4, 169–81.

Wicander, R and JS Monroe. 2007. Historical Geology: Evolution of Earth and Life Through Time. 5^th Edition. Thomson-Brooks/Cole. Belmont CA USA.

******

Developments in radiocarbon calibration for archaeology

Christopher Bronk Ramsey, Caitlin E. Buck, Sturt W. Manning, Paula Reimer & Hans van der Plicht








I like to think to myself, there are two kinds of comments on metafilter. Those I have favourited, and those I haven't favourited—yet.


These are the names of some interesting mefites.


zarq, Kattullus, Artw, filthy light thief, mathowie, Brandon Blatcher, kliuless, homunculus, delmoi, Blasdelb, infini, netbros, MartinWisse, jessamyn, nickyskye, Rory Marinich, emilyd22222, Burhanistan, stbalbach, Joe Beese, divabat, shakespeherian, flex, hippybear, y2karl, The Whelk, joseph conrad is fully awesome, the man of twists and turns, empath, Rhaomi, Iridic, blahblahblah, hadjiboy, grumblebee, Trurl, brundlefly, not_on_display, Miko, fearfulsymmetry, adamvasco, Bora Horza Gobuchul, sciatrix, ChuraChura, Nomyte, quin, flapjax at midnite, twoleftfeet, klangklangston, Confess, Fletch, sweetkid, l33tpolicywonk, JHarris, jjray, roomthreeseventeen, Effigy2000, reenum, Horace Rumpole, madamjujujive, ericb, KokuRyu, loquacious, Rumple, pjern, miss lynnster, crunchland, oneswellfoop, gerryblog, jeffburdges, ocherdraco, jiawen, codacorolla, Mick, griphus, cortex, dhruva, yeloson, gman, The Devil Tesla, azarbayejani, grouse, cashman, saulgoodman, cross_impact, baylink, matteo, davidjmcgee, JL Sadstone, nomadicink, aflakete, timsteil, St. Alia of the Bunnies, Taft, orange swan, ardgedee, vacapinta, hermitosis, Twang, serazin, desjardins, HuronBob, daveadams, Fizz, elizardbits, Toekneesan, East Manitoba Regional Junior Kabaddi Champion '94, andoatnp, lalex, OmieWise, stoneweaver, marxchivist, clarknova, Lexica, Juliet Banana, latkes, caddis, kmz, SkylitDrawl, zabuni, taz, Mayor Curley, the young rope-rider, escabeche, severiina, Chinese Jet Pilot, maudlin, plep, standardasparagus, nomisxid, rmd1023, LobsterMitten, cog_nate, languagehat, divined by radio, seanyboy, Sara C., acb, flatluigi, chavenet, Zarkonnen, Bunny Ultramod, WCityMike, spock, metaBugs, kinnakeet, peacay, Faintdreams, bardophile, fooljay, corb, peterme, GenjiandProust, binturong, plinth, NoraReed, Chrysostom, Pope Guilty, storybored, magstheaxe, jontyjago, barnacles, not_that_epiphanius, BuddhaInABucket, warbaby, cybercoitus interruptus, troll, minifigs, fings, lucia__is__dada, Pater Aletheias, 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ZenMasterThis, phyrewerx, FishBike, JoeXIII007, Faint of Butt, brilliantine, byanyothername, goodnewsfortheinsane, Who_Am_I, schroedinger, holmesian, nakedcodemonkey, revgeorge, scody, loosemouth, Michele in California, him, stavrosthewonderchicken, Memo, toodleydoodley, will, aleph, Mothlight, y0bhgu0d, adrianhon, joost de vries, finite, lupus_yonderboy, sixcolors, Mistress, tdecius, Astro Zombie, Ardiril, EmpressCallipygos, ADoubtfulTrout, emjaybee, ozomatli, XQUZYPHYR, KaizenSoze, wfitzgerald, Mitheral, snsranch, readery, Mr.Know-it-some, lesli212, typewriter, Z303, ericost, Methylviolet, thatwhichfalls, mudpuppie, Caduceus, dirtdirt, nobody, wenestvedt, 6am, leibniz, baphomet, Wolfdog, markkraft, SansPoint, syzygy, wintersweet, slater, Countess Elena, mokin, DoctorFedora, kagredon, scarabic, Servo5678, mikesch, casarkos, GhostintheMachine, Stark, Sleeper, dazed_one, yiftach, NortonDC, artof.mulata, peachfuzz, ntk, ericbop, benbrown, mediareport, sveskemus, i8ny3x, aniola, Dojie, mysticreferee, MisantropicPainforest, aurelian, Chipmazing, ixohoxi, unsupervised, at the crossroads, psoas, endquote, b., The Lady is a designer, jonp72, elgilito, TrarNoir, Kibbutz, en forme de poire, moonmilk, iamkimiam, beowulf573, lauratheexplorer, Threeway Handshake, Golden Eternity, sendai sleep master, Starmie, Babblesort, Winnemac, lexicakes, WPW, youarenothere, NekulturnY, dirigibleman, stagewhisper, dfan, egor83, immlass, Foaf, Medieval Maven, Skeptic, zoomorphic, 0bvious, swift, figurant, Avenger50, OrangeSoda, lemuring, tybeet, Navelgazer, joedan, solipsophistocracy, These Premises Are Alarmed, treyka, You Should See the Other Guy, fantodstic, inconsequentialist, Another Fine Product From The Nonsense Factory, ColdChef, scrump, TuxHeDoh, HyperBlue, feelinglistless, whatzit, gompa, Partial Law, ricochet biscuit, PWA_BadBoy, Tenacious.Me.Tokyo, kipmanley, ddbeck, dgaicun, rich, KevinSkomsvold, Laotic, khaibit, thatothrgirl, whyareyouatriangle, coriolisdave, disillusioned, gauche, Lord_Pall, movicont, joeclark, Gator, starman, Violet Hour, toddshot, ob1quixote, bluedaniel, jenkinsEar, Salvor Hardin, threeants, kneecapped, phunniemee, bearwife, tellurian, Enchanting Grasshopper, Kronos_to_Earth, John Cohen, CrayDrygu, ianbanks, ArgentCorvid, odinsdream, MetaMonkey, tamim, jamincan, ookamaka, degreezero, Weeping_angel, clockworkjoe, rosswald, misha, MaryDellamorte, disclaimer, MechEng, Dr Dracator, chundo, HP LaserJet P10006, chrisgregory, Tevin, Hartster, robocop is bleeding, fatllama, likeatoaster, lazaruslong, AlonzoMosleyFBI, lemonfridge, 2manyusernames, Steven Den Beste, MrMoonPie, Night_owl, Stacey, shivohum, QIbHom, tiaka, StrikeTheViol, knave, phrontist, badego, thewalrus, riffola, b2walton, backseatpilot, almostmanda, five fresh fish, geoff., criticalbill, nam3d, clueless22, Captain Najork, Wonton Cruelty, jedicus, Substrata, ominous_paws, crapmatic, beshtya, longsleeves, jhandey, JBennett, srboisvert, Currer Belfry, Joe in Australia, aaron, louche mustachio, xowie, Johnny Hazard, dry white toast, Namlit, BlackLeotardFront, oinopaponton, ariel_caliban, julen, marienbad, asavage, Ahab, edgeways, Telf, mmascolino, wittgenstein, FirstMateKate, selton, MiguelCardoso, jeeves, mandolin conspiracy, blue_beetle, Charlemagne In Sweatpants, attitude, Optimus Chyme, jacquilynne, Chan, dios, frumiousb, y6y6y6, mightygodking, bloated_guts, h00py, forrest, fullerine, raygirvan, The Winsome Parker Lewis, william_boot, Westringia F., scalefree, IvoShandor, bwg, chaff, donkeysuck, urbanwhaleshark, Woodroar, joannemullen, unliteral, russilwvong, nicebookrack, milarepa, PrincessNocturna, not_the_water, da5id, Mike Mongo, yourcelf, rjs, WhiteWhale, metrocake, Non Prosequitur, bluebelle, k8lin, patricking, Thin Lizzy, villanelles at dawn, sonika, Umpqua, mrgrimm, torisaur, Fence, cuban link flooded jesus, Abiezer, aisforal, -, mullingitover, I've wasted my life, TheLittlePrince, shothotbot, Stagger Lee, chaz, Arthur Phillips Jones Jr, Bukvoed, 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P.o.B., subject_verb_remainder, Wordshore, Mister Fabulous, tractorfeed, Sticherbeast, Gyan, suedehead, myopicman, overglow, Danila, christopher.taylor, mc_barron, MegoSteve, Bureau of Public Secrets, orthicon halo, AceRock, Benny Andajetz, Sunburnt, Dean_Paxton, mykescipark, Uther Bentrazor, Phlegmco(tm), snarkout, vidur, stp123, jkottke, CheeseDigestsAll, Deoridhe, hobbes, Lobster Garden, converge, cerebus19, legospaceman, voferreira, hama7, graventy, procrastination, dancingfruitbat, acro, nthdegx, jenfullmoon, achmorrison, HopperFan, howa2396, TedW, Thella, joannemerriam, Hollywood Upstairs Medical College, double block and bleed, SilentSalamander, philip-random, meech, cgs06, lohmannn, Diablevert, cenoxo, Awol, kimdog, Obscure Reference, Korou, deanc, Drinky Die, quanta and qualia, chronkite, philipy, Cat Pie Hurts, el io, young_son, jermsplan, danny the boy, Glibpaxman, maiamaia, digaman, fremen, bq, ErWenn, happyroach, brent, ratita, awfurby, Short Attention Sp, polywomp, anothermug, koeselitz, rtha, KathrynT, Ironmouth, nadawi, Frowner, zombieflanders, ArmyOfKittens, yoink, Marisa Stole the Precious Thing, sonascope, fourcheesemac, Dee Xtrovert, restless_nomad, muddgirl, verb, Greg Nog, stoneandstar, PhoBWanKenobi, Sys Rq, Smedleyman, palomar, jb, ShawnStruck, Ivan Fyodorovich, mek, blucevalo, Baby_Balrog, Sidhedevil, showbiz_liz, jetlagaddict, Corinth, idiopath, eriko, straight, FAMOUS MONSTER, Dysk, craichead, Slap*Happy, MCMikeNamara, octobersurprise, tonycpsu, flabdablet, Eyebrows McGee, Justinian, The 10th Regiment of Foot, davejay, cairdeas, nebulawindphone, mobunited, charlie don't surf, hoyland, The World Famous, ambrosia, localroger, kavasa, Jimmy Havok, geek anachronism, fraula, jaguar, ErikaB, Etrigan, jason_steakums, vorfeed, Malor, George_Spiggott, Holy Zarquon's Singing Fish, schmod, pracowity, maxsparber, audi alteram partem, Shepherd, Tomorrowful, ROU_Xenophobe, benito.strauss, anigbrowl, Pogo_Fuzzybutt, clockzero, EatTheWeak, adipocere, Joey Michaels, kyrademon, jsturgill, Ad hominem, mhoye, Squeak Attack, howfar, pyramid termite, hal_c_on, Civil_Disobedient, melissam, prefpara, gingerbeer, Celsius1414, drjimmy11, anansi, Doleful Creature, one more dead town's last parade, Thorzdad, Talez, ennui.bz, painquale, jscott, Kadin2048, The Card Cheat, sallybrown, Theta States, Forktine, emmtee, cstross, Cool Papa Bell, Bulgaroktonos, WidgetAlley, burnmp3s, winna, peacheater, kaibutsu, gingerest, Faze, ernielundquist, Ghostride The Whip, Dreidl, tyllwin, sotonohito, daq, raztaj, invitapriore, spicynuts, not that girl, Jilder, stammer, boo_radley, kirkaracha, joe lisboa, octothorpe, angrycat, internet fraud detective squad, station number 9, jscalzi, Consonants Without Vowels, Rustic Etruscan, Linda_Holmes, UbuRoivas, You Can't Tip a Buick, dejah420, bonehead, wuwei, tzikeh, No Robots, zippy, klanawa, allen.spaulding, Halloween Jack, game warden to the events rhino, justsomebodythatyouusedtoknow, Mrs. Pterodactyl, billiebee, Decani, leotrotsky, Horselover Phattie, nickrussell, spaltavian, It's Raining Florence Henderson, Ursula Hitler, kozad, Maias, Solon and Thanks, fatbird, deanklear, R. Schlock, vanar sena, Sova, XMLicious, titus n. owl, poffin boffin, Francis, His thoughts were red thoughts, Acromion, Lord Chancellor, Daily Alice, headnsouth, evidenceofabsence, Jeanne, saucysault, saturnine, gurple, Jimbob, kafziel, jefgodesky, windykites, StickyCarpet, Dr. Zira, Sequence, dances_with_sneetches, Pastabagel, Poet_Lariat, feckless, zizzle, Atom Eyes, olinerd, nasayre, nanojath, Hoopo, BitterOldPunk, Space Kitty, Madamina, Avenger, cjorgensen, bicyclefish, lunasol, wierdo, barchan, Metroid Baby, Nattie, Mental Wimp, Rodrigo Lamaitre, 0xFCAF, Salieri, feloniousmonk, seanmpuckett, Bromius, alms, DNye, George Clooney, Inspector.Gadget, allthinky, sparklemotion, cooker girl, bonaldi, Fezboy!, valkyryn, Thoughtcrime, entropone, lriG rorriM, msalt, Doktor Zed, weston, amuseDetachment, trackofalljades, colie, Sing Or Swim, cmgonzalez, krinklyfig, Catseye, Phalene, Kitteh, clavdivs, smackfu, ibmcginty, Jacqueline, jeather, Dip Flash, Doublewhiskeycokenoice, flaterik, two or three cars parked under the stars, Tell Me No Lies, Durn Bronzefist, greekphilosophy, obiwanwasabi, The corpse in the library, KHAAAN!, thecjm, RedEmma, enn, fleetmouse, jammy, teleri025, Anything, DrMew, oceanjesse, availablelight, The Gooch, Amanojaku, Panjandrum, lesbiassparrow, LogicalDash, Gygesringtone, Seymour Zamboni, mistersquid, tkchrist, shii, lord_wolf, Capt. Renault, Mikey-San, Lyn Never, ovvl, DarlingBri, We had a deal, Kyle, dubold, stinkycheese, edheil, Jpfed, chapps, DirtyOldTown, Rhomboid, jess, dixiecupdrinking, Carol@ILPoisonCenter, liza, the jam, shmegegge, Humanzee, IAmUnaware, girlmightlive, suelac, mazola, leopard, PontifexPrimus, dephlogisticated, salishsea, feckless fecal fear mongering, to sir with millipedes, jfwlucy, joyceanmachine, kewb, three blind mice, mdn, 23skidoo, xarnop, Wossname, jtron, EarBucket, atrazine, Podkayne of Pasadena, Snarl Furillo, TwelveTwo, theora55, inturnaround, thelonius, Hammond Rye, Flunkie, bondcliff, Kid Charlemagne, Alice Russel-Wallace, ersatz, bakerina, specialagentwebb, Anitanola, Aizkolari, discopolo, Karmakaze, Grimgrin, jbickers, brokkr, unSane, T.D. 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oddman, Wolof, tylerkaraszewski, dw, mannequito, fleacircus, lumpenprole, sio42, chemoboy, Artful Codger, Surfurrus, LarryC, sciencegeek, Garm, mr_roboto, COBRA!, Roger Dodger, LastOfHisKind, Fiasco da Gama, Mister_A, de, shen1138, Bella Donna, Unified Theory, lattiboy, jfuller, darkstar, Segundus, jefficator, madajb, zachlipton, atomicstone, drlith, OverlappingElvis, librarylis, vicx, TypographicalError, FelliniBlank, betweenthebars, PareidoliaticBoy, letitrain, If only I had a penguin..., kbanas, JPD, bilabial, twirlypen, harriet vane, Mayor West, 2N2222, motty, nutate, Sangermaine, colfax, Hildegarde, this is a thing, asok, haveanicesummer, billyfleetwood, cell divide, billb, Eideteker, qvantamon, phoebus, abc123xyzinfinity, Dashy, sukeban, adamdschneider, nathancaswell, Foci for Analysis, RokkitNite, kalessin, dancestoblue, vibrotronica, dhartung, flug, Nelson, regicide is good for you, oulipian, which_chick, TwoWordReview, weinbot, ctmf, sevenyearlurk, Xoebe, Balisong, mondo dentro, Brainy, cogpsychprof, jennaratrix, drewb, 0xdeadc0de, retrograde, JaredSeth, handee, nushustu, Mitrovarr, melissa may, bonje, mkultra, pompomtom, lumensimus, dog food sugar, exogenous, fshgrl, twist my arm, lastobelus, zamboni, gadge emeritus, facetious, [expletive deleted], dng, Houstonian, tocts, francesca too, knuckle tattoos, RonButNotStupid, fight or flight, BlueJae, breath, Nothing, PlusDistance, blue t-shirt, triggerfinger, oliverburkeman, Aya Hirano on the Astral Plane, infinitywaltz, Kit W, MissySedai, ThePinkSuperhero, stavrogin, Fuka, r_nebblesworthII, Pollomacho, bitter-girl.com, msconduct, fredludd, A Terrible Llama, digsrus, dontjumplarry, jacalata, nikitabot, mosch, naoko, Copronymus, joshwa, Drexen, Go Banana, MeghanC, Vysharra, kristi, jimmythefish, The Bellman, Happy Dave, uni verse, subdee, emilycardigan, Coda, neuromodulator, Scientist, metaman livingblog, zutalors!, terrapin, phearlez, atchafalaya, Think_Long, mippy, piratebowling, Cookiebastard, 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Life is—
As life does.
Life that is–
And life that was.

If you need a friend just say hello.
Being kind to each other is often harder than not, don't forget the lessons we should have learned had we thought, externally distinct from the internal wars never fought. Be kind to yourself.