02 January, 2011

Not So Much An Explosion...

...as a long, slow-burning fuse.

Dr. Joe Meert and colleagues may have discovered evidence of Ediacaran fauna stretching back a lot longer than previously thought.  And it's all because their driver had a mild stroke in the field, leaving them stranded a bit and with nothing to do but nose around the rocks of Maly Karatau looking for fossils.  They found some.

Our work in the lab is what provided the first surprise. The general consensus is that the Ediacara fauna reached their zenith around 565 Ma following the last of the severe glacial epochs. In fact, many argue that the so-called Snowball Earth episodes provided the stress necessary for the evolution of complex life during the Ediacaran-Cambrian interval. But the age of the rocks came back as 766 Ma. This is more than 100 million years older than the previously reported occurrences of Nimbia and was a bit of a shock. Furthermore, our study of stable isotopes on the glacial deposits indicated that they are most likely of Marinoan age (~650 Ma). Since the fossils were found stratigraphically well below these glacial rocks, our age estimate made even more sense. 

Meert, J.G., Gibsher, A.S., Levashova, N.M., Grice, W.C. and Kamenov, G.D., Glaciation and ~770 Ma Ediacara (?) Fossils from the Lesser Karatau Microcontinent, Kazakhstan, Gondwana Research (large pdf). doi10.1016/j.gr2010.11.008. 
More at the Panda's Thumb, including more about the geology of the area.  Or, for the full stratigraphic goodness, you could go read the whole paper, which includes some mouth-watering photos of ancient tillites and one very attractive rock that looks like a glacier scratched it up just last Ice Age.

Now, if this paper gains any traction, you'll probably see headlines shrieking that the Ediacaran fauna have positively without doubt been pushed back another 100 million years ZOMG.  That could be the case.  But the authors of the paper are careful not to jump all the way overboard.  This could prove multicellular animals were tooling around the oceans long before we suspected.  Or... not so much.  They may be determined not to have been multicellular at all, in fact.  Lots of research still needs to be done, and you can tell from the photos that these soft-bodied little critters are subtle and hard to suss.

But that's ultimately not so important as the fact that life on Earth spent a long, long time evolving its way toward complexity.  It got there gradually, not all at once in some huge, instantaneous explosion.  It's not like critters went to bed single-celled and got up on the first morning of the Cambrian as multicellular armored beasties.  That is just not how it went.  If you still want to think in terms of an "explosion," you'll have to envision a blowup that lasted up to hundreds of millions of years - longer, in fact, than it took us to evolve from shrew-like mammals shivering in the shadows of dinosaurs to nekkid apes shivering in a stiff winter breeze.

As far as we can tell, life spent a long time futzing around with single cells, lounging together as microbial mats, before venturing out in a desultory sort of way to become wee little multicellular things that eventually discovered the joys of predator-prey relationships and the importance of armor.  Evolution can happen quickly, and sometimes does -once a threshold is reached, it's not implausible that innovation can take off in all kinds of directions.  But it's not precisely an explosion.  And it's certainly not the kind of nearly-overnight sensation the IDiots and cretinists lust for.  It may look fast, but that's only if you don't understand geologic time.  This paper, should it prove that the authors' conclusions are right and the Ediacaran fauna spent an additional hundred million or so years lurking around in soft-bodied multicellular glory, is merely an additional slap in the face to those who cling with grim determination to a figure of speech.  We already knew the "explosion" took at the very least tens of millions of years to go boom - far more than enough time for plain ol' unsupernatural evolution to do its thing.  No gods need apply.

Still, it's exciting to think that life on Earth consisted of more than just microbial mats as early as three-quarters of a billion years ago. 

Incidentally, Dr. Meert has his own blog, Science, AntiScience and Geology, where you can read one of the greatest Blogger profiles ever written:
I have a Ph.D. from By Bayou University where I am employed as a Professor of Hydrocephalic Earth Studies and Structure. My research is aimed at demonstrating the utter lunacy of young earth creationism. Oh, I am not 549 years old, I don't endorse astrology and I found it interesting that 1457 was the year of the rat, but I have no idea why this blogger puts such information into a bio.
I think I just fell a little bit in love just then...


Helena Mallonee said...

"It's not like critters went to bed single-celled and got up on the first morning of the Cambrian as multicellular armored beasties."

So, intelligent design is like Kafka's "Metamorphosis," except prompted by God?

Lyle said...

Given the fairly poor preservation of rocks from the Edicardian, and the recent consensus on snowball earth, it would only make sense that multicellular life was tried several times. The question would really be when did the mitochondria and cholorplasts become elements of complex cells. As other blogs have noted multicelluar life is not really possible until you get mitochondria to provide the energy.
In this period we are dealing with a lot of time, and its likley that several attempts were made, and some may have been unsuccessful as the earth went back to slushball/snowball mode.