Francevillian biota - evidence for *ancient* multicellular life.

The textbook opinion on the origin of multicellular life on Earth is that it started - very rapidly it should be added - a little less than 600 million years ago with the so-called "Ediacara" fauna (named so after a site in Australia where they were first described). In the following period of Earth's history, the Cambrian (see also, as a buzzword, the "Cambrian Explosion"), the 'modern' lineages appear (plus a plethora of now-extinct ones), and from there, the history of life more or less goes as we know it. Considering the overall age of the Earth (around 4.6 billion years), and given that life seems to have been around very early (that story is also updated further and further), and single-celled organisms practicing photosynthesis, enriching the atmosphere with oxygen relatively early (around 2.4-2.3 billion years ago), it seems strange that multicellular life would appear after a huge aeon (well over a billion years) during which seemingly 'nothing' happens (nothing we can see, anyways).

That is, however, not the whole story. There's been a sensational discovery from the Precambrian (around 2.1 billion years ago - around 1.5 billion, or 1500 million years earlier - I'm writing it out like that because I mean "short" billions ), which shows in such ancient time (see link), that there have been macroscopic (ranging from a few cm to over ten of centimeters in size) structures of clearly biogenic origin. The general consensus is that these represent an early experimentation of life with multicellularity - literally aeons before life as we know it started. What happened with it?

One interpretation - as they note in the article, these "Francevillian biota" have disappeared from the younger strata, which suggests that they very probably went extinct. Note that this isn't my idea originally, but the argumentation line is verymuch sound to me, but there is one peculiar piece of evidence of what may have happened: a couple of hundred million years later, Earth was hit by a duo of truly catastrophic asteroid impacts - first the asteroid that formed the (originally circa 250-300 kilometer sized) Vredefort Crater in South Africa. A couple of hundred million years later, another body of similar size hit the Earth and formed as similarly-sized crater, the Sudbury Crater in Canada. One of these impacts alone would probable have been more than enough to wipe out most life on Earth (note: each of the craters is almost twice the size of the Chicxulub crater that is implicated in the extinction of the dinosaurs!). The fact that two of these events happened would quite conviniently explain why multicellular life went completely extinct, and didn't evolve again for over a billion years.

user link on journals.plos.org

EDIT: apparently, I accidentally deleted a passage back there. I just fixed that.

Now that's pretty neat. I may not be able to access (or understand) the full article, but it's some interesting stuff. As many a person who was once a child, I'm still fond of paleontology and similar things (initially dinosaurs, but there's a lot more neat stuff out there), so it was cool to learn about this, what with not really keeping up on things for the past few decades.

It's a bit off-topic, but I'm pretty sure the dinosaurs in kids' books on them now must have feathers, which is a bit of a change from when I was growing up. I also recall there's a book somewhere in which some people did illustrations along the same lines as those done based on dinosaur skeletons of modern animals, based on their skeletons, with often interestingly unusual results. Can't remember the title, sadly.

On Wednesday, January 20th, 2016 at 11:29 pm, vega7285 said:

This is a relatively recent discovery (past two years, the paper I quoted above is from 2014). But yes, there's a lot of new stuff that came out in recent years. For the future, I'll try to occasionally post over here what I come across.

I must admit its the first time I've heard about that particular book. I must say though, while _many_ dinosaurs were from modern view of research feathered (the advanced theropods - two-legged dinosaurs that were mostly but not all carnivorous - were for sure). On the other hand most other groups of dinosaurs, in particular the sauropods (the really huge, long-necked dinosaurs), for sure were scaly like on the old images (maybe not as bulky, if you look at old paintings, dinosaurs look so obese ). One thing that old images completely get wrong is that they have the tail dragging on the ground whereas in actuality it was held above the ground in basically all dinosaurs.

That's really cool. It stands to reason, too, that life probably started to evolve at least a couple times before the current chain of evolution before some catastrophic event set it back to the beginning, essentially.

As for dinosaurs, aren't birds and crocodiles the closest modern life forms to them? It's funny how inaccurate the science text books from grade school (back in the 1980's, in my case) are by now.

It wouldn't be the least bit surprising if they find even more examples of life that precedes the earliest known time period for life. On these time scales, catastrophic events that wipe out large portions of life on Earth are much more common. I'm no geologist, so I'm uninformed as to exactly how far back that strata are viewable in most places (though - there are places where subduction has pushed them to the surface!)

Good development. We're going to have to re-think our ideas about when life originated.