Early Life in Death Valley

May 8, 2014 10:19 AM

What if complex life didn't evolve in the oceans?
posted by brundlefly (14 comments total)

"Many were increasingly of the opinion that they'd all made a big mistake in coming down from the trees in the first place. And some said that even the trees had been a bad move, and that no one should ever have left the oceans Death Valley."
posted by jedicus at 10:27 AM on May 8, 2014 [11 favorites]

Much to their astonishment, Knauth and his graduate student at the time, Mark Beeunas, discovered that a 1.2-billion-year-old desert karst in central Arizona called the Mescal Limestone showed geochemical signs of life during the Precambrian eon “It was surprising because, according to all of the textbooks, the Precambrian lands were totally barren,”

Needing more evidence to buttress his paradigm-challenging claim, Knauth went in search of signs of life in Death Valley, sampling an unusual ridge of black quartz on top of the Beck Spring Dolomite. Back in the lab, geochemical analysis revealed low levels of carbon 13; photosynthesizing organisms had lived there, lots of them, he concluded. And where there are geochemical signs of life, there could also be microfossils.

I used to live just south of Death Valley. When it rained enough to flood the wadis, shrimp hatched out in the desert. It took weeks for the water to completely dry up. There are lakes in that area that exist for about two months out of the year. It's quite a fascinating landscape.
posted by Michele in California at 10:53 AM on May 8, 2014 [3 favorites]

intriguing to have this near the borehole article about how little we really know about our planet.
posted by k5.user at 11:27 AM on May 8, 2014

Seems to add a little more heft to some of the Panspermian theories for the origins of life on Earth, dunnit?
posted by saulgoodman at 11:39 AM on May 8, 2014

Now I feel kind of bad for the folks who just animated that sequence in Noah that was the only watchable five minutes in the entire film...but on topic, this is really fascinating. It would be amazing to discover eventually that there were actual tandem processes going on both above and below the surface of the water which later merged during the various mass extinctions and climate shifts.
posted by trackofalljades at 11:43 AM on May 8, 2014

I was wondering what they meant by "complex". Turns out they mean "multicellular".

I would have said that "complex" was development of Eukaryotes. (Which happened in the ocean.)
posted by Chocolate Pickle at 11:45 AM on May 8, 2014 [1 favorite]

What if complex life didn't evolve in the oceans?
posted by brundlefly

Eponysterical?
posted by Behemoth at 12:19 PM on May 8, 2014 [3 favorites]

And to think, my manatee is always going on and on about how humans need to evolve back into the water to "complete the cycle and return home" Man, is he ever going to be embarrassed.
posted by boubelium at 12:20 PM on May 8, 2014 [2 favorites]

I wouldn't be at all surprised to learn that simple life forms had evolved and persisted in continental or marginal marine environments for a very long time. As Stephen Jay Gould put it, the "Age of the Dinosaurs" and the "Age of Man" really take a back seat to the Age of the Bacterium. Microbes have exerted a profound influence on the planet's chemistry and the cycling of essential compounds for billions of years, and in today's world they occupy nearly every conceivable environment in the atmosphere and upper lithosphere. The Great Oxygenation Event, the Permian-Triassic Extinction, perhaps the advent of biomineralization... the fate of all other life on earth is inextricably linked to these simplest of organisms.

The more interesting question would be: did complex, multicellular organisms evolve in terrestrial environments before they did so in the ocean? It's true that preservational biases skew the fossil record toward marine organisms, but I am still skeptical of Dr. Knauth's second hypothesis ("Knauth thinks that the reverse may have occurred; land-based animals crawled into the sea, spawning marine metazoans with shells"). The creation of shells, and the incredible evolutionary event known as the Cambrian Explosion, is one of the enduring mysteries of paleontology. There are lots and LOTS of ideas as to how so many new, biomineralizing animals could appear so quickly in the fossil record, and this is just one of them. As is usually the case, this enormous change probably had a whole bunch of linked environmental causes, working and interacting simultaneously. In the interval just before the Cambrian Explosion, worldwide carbon isotopes record a simultaneous negative delta-13 anomaly, so we know that the carbon cycle was shifting and rearranging itself around a new equilibrium. It may have had to do with (wait for it!) more efficient pooping, which exported organic matter more quickly to the seafloor, which encouraged animals to dig down into the microbe-dominated sediments in search of food, which ventilated the sediments and created a pool of microbially generated carbonates ready for sediment-dwellers to convert into shells... But, all theorizing aside, I don't know that we've seen any unambiguous evidence of terrestrial organisms migrating into the oceans. Hell, maybe those first poop-burrowing animals came down from the seashore, but at this point I can't vouch for their origins either way. Knauth's claim is a bold one, and we'll be able to evaluate it more stringently as we gather more data.


Semi-related: Dr. Shuhai Xiao, who is cited in this article, has done some very interesting work on early animal embryos preserved in the Doushantuo Formation. The animals from this period (the Ediacaran, or latest Precambrian) are strange creatures that don't seem to have any analogues or descendents in the modern animal kingdom.
posted by Vic Morrow's Personal Vietnam at 12:22 PM on May 8, 2014 [4 favorites]

Radiates, vegetables, monstrosities, star spawn — whatever they had been, they were men!
posted by GenjiandProust at 12:29 PM on May 8, 2014 [1 favorite]

Oh, and with regard to taphonomic biases, allow me to paraphrase the noted paleontologist D.H. Rumsfeld: the absence of evidence is not evidence of absence... but it's not evidence of presence, either.
posted by Vic Morrow's Personal Vietnam at 12:54 PM on May 8, 2014

I evolved some complex life in my fridge just last week.
posted by Hairy Lobster at 2:20 PM on May 8, 2014 [1 favorite]

As per the Transformers thread there's no hard and fast rule for how life evolves:

Whereas life elsewhere in the cosmos usually evolved through carbon-bonding, here it was the interaction of naturally occurring gears, levers and pulleys that miraculously brought forth sentient beings.
posted by any portmanteau in a storm at 2:28 PM on May 8, 2014 [1 favorite]

"The Beck Spring formation stretched before us, angular and dusty with few signs of life. But to Knauth’s mind, its surface was once a glistening green, covered by photosynthesizing cells, cyanobacteria and algae. These simple organisms turned sunlight into energy and oxygen, leaving behind the telltale trail of carbon 13. Rainwaters flushed through the thick wet mats of living cells on the surface, sometimes pulling individual cells into the karstifying holes, where they became trapped between pieces of rubble. Iron in the water adhered to the trapped, rotting microbiota, hardening the structure. The new fossils were gradually encased in tiny seams of crystallizing silica (quartz) that grew between the bits of rubble, cementing them together."

I don't understand how the chert (quartz) was forming in the karst holes under ambient conditions. But assuming that it was, then how can he show that the micro-fossils weren't simply blown in on the wind? The western margin of Larentia would have been coastal (assuming it was dry in the first place) in the late Proterozoic.

Also aren't there an awful lot of Stomatite fossils showing lots and lots of marine unicellular life from the same period?
posted by Long Way To Go at 9:00 PM on May 8, 2014