The Great Unconformity

June 23, 2013 3:27 PM

The results of the Cambrian explosion are well documented in the fossil record, but its cause -- why and when it happened, and perhaps why nothing similar has happened since -- has been a mystery. Now a recent paper in Nature (abstract) suggests that the answer may lie in a second geological curiosity -- a dramatic boundary, known as the Great Unconformity, between ancient igneous and metamorphic rocks and younger sediments.
posted by Long Way To Go (17 comments total)

"Horizontally-bedded, basal-conglomeritic, Early Cambrian Tapeats Sandstone is resting directly upon vertically-foliated Early Proterozoic Vishnu Schist."
BOOM
posted by Stonestock Relentless at 3:38 PM on June 23, 2013 [6 favorites]

As always if anyone would like the paper itself please feel free to memail me with an email address I can send a PDF to and a promise to not distribute it further - for the purposes of this academic discussion we are currently having of course.
posted by Blasdelb at 3:43 PM on June 23, 2013 [5 favorites]

Wow... I don't have the geology background to fully follow that, but... Simply awe-inspiring, that we have such a huge gap in our planet's geologic evolution.

/ Of course, we all know that the eventual use of the Atlantean weapon-of-last-resort caused the rifting of Rodinia, and the Great Unconformity, and even the "Snowball Earth" as an unexpected side-effect.
posted by pla at 3:49 PM on June 23, 2013 [1 favorite]

I thought it was the Thetans that caused this... ;-)
posted by MikeWarot at 3:54 PM on June 23, 2013 [1 favorite]

No, they're responsible for the triclosan in toothpaste.
posted by sneebler at 4:12 PM on June 23, 2013 [4 favorites]

I think I might have to write a NaNoWriMo novel just so I can call it 'The Great Unconformity'.
posted by jeffkramer at 4:22 PM on June 23, 2013 [1 favorite]

"Horizontally-bedded, basal-conglomeritic, Early Cambrian Tapeats Sandstone is resting directly upon vertically-foliated Early Proterozoic Vishnu Schist."
posted by Stonestock Relentless

You've been waiting for this FPP, haven't you stonestock?
posted by spitbull at 5:11 PM on June 23, 2013 [5 favorites]

Of course, we all know that the eventual use of the Atlantean weapon-of-last-resort caused the rifting of Rodinia, and the Great Unconformity, and even the "Snowball Earth" as an unexpected side-effect.

Throw in some Daleks and perhaps the noble but pointless self-sacrifice of an annoying companion nobody liked anyway, and that would make a pretty good Doctor Who episode. It's about time for the series to offer up yet another episode detailing yet another destruction of Atlantis.
posted by RonButNotStupid at 5:14 PM on June 23, 2013

Rocks is just rocks, until...

THE GREAT UNCONFORMITY!

Then things start to get interesting.
posted by BlueHorse at 7:03 PM on June 23, 2013

What a fascinating hypothesis and a wonderful post - thank you! Their argument makes a lot of sense, and they seem to have made a fairly convincing case for the broad-scale increase in weathering rates as the basis of the Great Unconformity. How controversial is their idea? Has this been considered before?

Given that biomineralization seems to be characteristic of the biota of the Cambrian explosion, the leap from the change in ocean chemistry (notably, increases in HCO₃^- & Ca²⁺) to the Cambrian explosion is intuitive, but I'm not sure they made that case very thoroughly. What's the next step for pursuing the evolutionary aspect of their hypothesis? What kinds of evidence would allow us to establish causality, i.e. that this change in ocean chemistry was a major driver of the diversification of the Cambrian explosion? What sorts of processes can we infer from the pattern of diversification that we observe in the fossil record if we assume that this hypothesis is correct?

I also wonder what we can learn about ecosystem ecology from this idea. Are there any fundamental ecological patterns in the way that life changed in response to the broad-scale change in biogeochemical cycling at the time of the Unconformity? Can we apply any of what we learn to the anthropogenic changes in biogeochemical cycling that we're observing today, or do these processes not operate at that scale?

Thanks again for the fantastic post! Exploring this issue was a great way to spend my Sunday.
posted by dialetheia at 7:03 PM on June 23, 2013 [2 favorites]

Fascinating. I watched a documentary recently that connected shifts in climate to changes in geology and ecosystems. One idea went something like this: drier conditions led to shrinking forests and spread of grasslands; grasses incorporate silica in their leaves; the vast extent of grasslands provided bioavailable silica that washed into the oceans; the increase in silica in oceans led to a population explosion of diatoms, which form the base of ocean food chains; this led in turn to the expansion and diversification of larger marine organisms. Wonderful to think the spread of grasses on land led to changes in ocean ecology.
posted by binturong at 7:14 PM on June 23, 2013 [3 favorites]

"Horizontally-bedded, basal-conglomeritic, Early Cambrian Tapeats Sandstone is resting directly upon vertically-foliated Early Proterozoic Vishnu Schist."

I thought this was some geology/theology play on words and I was so confused because well, I get Vishnu, but who is Tapeats and of what religion are they the creator of life?

Now I know that Vishnu Schist, Brahma Schist and Rama Schists are all real names of different kinds of rock, as well as Zoroaster Granite. The internet also provided surprisingly good answers as to how they got those names.
posted by myelin sheath at 8:09 PM on June 23, 2013 [2 favorites]

Vishnu Schist sounds like a handle from a cyberpunk novel.
Which is to say, it sounds awesome.
posted by Mister Moofoo at 8:49 PM on June 23, 2013

Vishnu Schist sounds to me like a character name from a Pynchon book, which is also awesome.
posted by stavrosthewonderchicken at 11:18 PM on June 23, 2013 [1 favorite]

Thanks, Long Way To Go, for a fascinating post!

Also, I want to form a band called "Zoroaster Plutonic Complex."
posted by Kattullus at 5:29 AM on June 24, 2013

why and when it happened, and perhaps why nothing similar has happened since -- has been a mystery.

I like to think of it more like a secret. One that humans are generally better off not discovering.
posted by FatherDagon at 11:14 AM on June 24, 2013 [1 favorite]

Jerry Coyne: What caused the Cambrian explosion?
posted by homunculus at 4:39 PM on June 24, 2013