What sparked the Cambrian explosion?
February 19, 2016 7:49 PM   Subscribe

An evolutionary burst 540 million years ago filled the seas with an astonishing diversity of animals. The trigger behind that revolution is finally coming into focus , according to the journal Nature. posted by MoonOrb (37 comments total) 31 users marked this as a favorite
 
Spoiler: It's not Celestials (although the main image does appear to suggest Great Old Ones, and the text almost describe them like that).

Somehow, I have never heard of the Ediacaran before now. Fascinating.
posted by Mezentian at 8:24 PM on February 19, 2016 [1 favorite]


The trigger behind that revolution is finally coming into focus , according to the journal Nature.

Dammit, I said I was sorry!!!!
posted by eriko at 8:40 PM on February 19, 2016 [2 favorites]


I knew it had to be Nacho Cheese Doritos.
posted by perhapses at 8:45 PM on February 19, 2016 [3 favorites]


the ediacaran is just yes album covers
posted by Zerowensboring at 9:01 PM on February 19, 2016 [22 favorites]


Based on what I learned about the Ediacaran in paleontology classes, this article does a decent job of describing the flora for non-specialists.

In case anybody cares, the Cambrian Explosion is considered one of the big unexplained mysteries in paleontology/paleobiology. Between that and the transitions to eukaryotes and multicellular life, you've got the trifecta of great mysteries for geologists and biologists to work at for years and years to come.

Plus, if we ever get our asses in gear enough to see about life on other planets, whatever we've learned from studying these mysteries will prove very useful. Or conversely, what we learn there may help us figure out this mystery.

Regarding the origin of life itself, I think the smart money is on abiogenesis based on the Miller-Urey experiment, with panspermia as a possible alternate.

I'll be watching the news on this one for years.
posted by Strudel at 11:35 PM on February 19, 2016 [4 favorites]


One possible misconception about the Cambrian explosion is that all the modern animal phyla appeared at that time. Calibrated molecular clock data shows that some phyla actually diverged as far back as the Cryogenian, but didn't diversify until the Cambrian explosion. It's a small distinction, but I think it's worth noting.
posted by deadbilly at 12:25 AM on February 20, 2016 [1 favorite]


I thought Miller-Urey was a bit old hat, given that it started from conditions we don't now think were the case? And panspermia, even if true, doesn't answer the question.

I like the geothermally driven molecular assembly in clay matrix idea myself, but mostly because it's nice to think of processes that are independent of the sun.
posted by Devonian at 1:17 AM on February 20, 2016 [1 favorite]


Well, I think we can chalk this one up to Intelligent Design then.

But, more seriously, I'm not entirely sure what I read, but the Miller-Urey experiment seems pretty cool, if nothing else. For the first time in my life, I wish I had studied more biology than I did.

Or science history. I'd be down with studying science history.
posted by Mezentian at 1:31 AM on February 20, 2016 [1 favorite]


Articles like this always make me wish I was a lot smarter than I actually am. It's fascinating, but I only understand about half of it.
posted by Solomon at 3:18 AM on February 20, 2016


The question I have that I don't see clearly addressed and maybe someone with more depth to their biological knowledge could address...

Why would the mere existence of oxygen create complexity in body-structures? And that complexity would necessitate predation to support it? Is it merely a factor of increased oxygen opens a space of greater/novel possibilities for the randomness of evolution to work within?
posted by kokaku at 4:05 AM on February 20, 2016


It's a cycle - you get more energy from your food if you have an oxygen-based metabolism, which means you can evolve the ability to predate on things with less energy. Eating things that have already eaten other things will also get you more energy. This puts evolutionary pressure on prey to evolve defences or escape mechanisms, and you then evolve counter-counter measures... pretty soon, you've all got complex mechanisms due to both having more energy and the need to either eat things that don't want to be eaten or being the latter.

Evolution isn't random. Mutation is random, but survival of the fittest is driven by rules. Evolution is the combination of the two.

Oxygen is like electrification. You wouldn't have microwave ovens without electricity, but when electricity first turned up we were still a very long way from them. The electricity didn't create complexity, it enabled it.
posted by Devonian at 4:32 AM on February 20, 2016 [12 favorites]


thank you

(also... eponysterical answer?)
posted by kokaku at 4:34 AM on February 20, 2016 [4 favorites]


Geologic clock-shaped timeline of Earth's history, for anyone else looking for context.
posted by XMLicious at 5:00 AM on February 20, 2016 [1 favorite]


tl;dr version: The trigger behind that revolution is finally coming into focus and until it finally comes into focus, it's hazy. Unclear. Looks like oxygen, but with something. Quite possibly several somethings.
posted by hat_eater at 5:20 AM on February 20, 2016 [1 favorite]


I thought it was quite clear: carnivores. All of a sudden animals needed to defend themselves, leading to all sorts of evolutionary changes. The oxygen explanation been proposed in the past and appears to be a contributor as well.
posted by CheeseDigestsAll at 6:57 AM on February 20, 2016


Well, I think we can chalk this one up to Intelligent Design then.

"Intelligent Explosion" vs. "The Blind Bombmaker".
posted by the quidnunc kid at 7:35 AM on February 20, 2016 [2 favorites]


the ediacaran is just yes album covers

No, you're thinking of the Rogdeanian.
posted by ZenMasterThis at 8:49 AM on February 20, 2016 [4 favorites]


> "Intelligent Explosion" vs. "The Blind Bombmaker".

Is that the next summer blockbuster? They're really digging deep into their back catalogue, aren't they?
posted by benito.strauss at 8:54 AM on February 20, 2016


Just as I've always suspected: use of oxygen-based respiration is problematic.

If your species can't get by without the use of a poisonous gas, you have no business being a species. At the very least, you have no business eating other species. total dick move.
posted by You Can't Tip a Buick at 10:23 AM on February 20, 2016 [2 favorites]


Yeah. I'm later. Fish sex and eyeballs.
posted by Devonian at 10:23 AM on February 20, 2016 [5 favorites]


CheeseDigestsAll: I thought it was quite clear: carnivores. All of a sudden animals needed to defend themselves, leading to all sorts of evolutionary changes. The oxygen explanation been proposed in the past and appears to be a contributor as well.

I believe the point was that a higher oxygen level *allowed* carnivores. That carnivores in general need to be more complex/faster/better armed that that which they predated on, and anerobic metabolisms couldn't support that. The survey of low oxygen ecosystems around the earth today was particularly suggestive.
posted by tavella at 10:55 AM on February 20, 2016 [1 favorite]


I like their answer : Diversity results from predation enabled by oxygenation. Very logical.
posted by jeffburdges at 11:11 AM on February 20, 2016


It's a dog eat dog world
posted by iotic at 11:14 AM on February 20, 2016


I'm not saying it was aliens, but...
posted by mrbigmuscles at 11:22 AM on February 20, 2016


I also like the current theory that it was becoming more carnivorous that allowed our brains to develop so drastically when the hominids diverged from the rest of the apes. I think that and the basic diversity of life being driven by predation means we are all morally impelled to hunt, kill and eat Whole Food shop assistants in order to drive the next stage in life's majestic story.
posted by Devonian at 11:23 AM on February 20, 2016 [3 favorites]


Interesting that it is framed in terms of predation - since the question is really one of how cooperation between single celled lifeforms occurred. Predation as a pressure certainly makes a lot of sense. Assuming that's correct, it still leaves a lot of questions about how the progression occurred - presumably from simple colonies and symbiosis, through to stable and unified multicellular organisms.
posted by iotic at 11:23 AM on February 20, 2016


Aren't most large steps towards cooperation between single celled lifeforms earlier? We observe an enormous diversification of multi-cellular life in the Cambrian explosion, but all the basic mechanisms behind multi-cellular life surely existed earlier, no?

I suppose sexual selection would kick in one animals start crawling around more, well presumably gender predates the Cambrian. I'd imagine that's first a consequence and second a magnification factor though. Also, there are no proposals that changes in sexual selection created the explosion listed on wikipedia, so maybe sexual selection doesn't really run crazy until after the Cambrian. Anyone know?
posted by jeffburdges at 11:54 AM on February 20, 2016


The elements may have been there, but wasn't there somewhat of a "sea change" in terms of complexity and diversity of multicellular life, in the Cambrian? That seems the interesting thing to elucidate - how comple organisms arise from simple ones. And why there was such a great explosion, only a small subset of which survived to contribute to today's biosphere? Certainly understanding the environmental factors and evolutionary pressures prompting the change would be a useful step towards answering these questions, at least.
posted by iotic at 12:09 PM on February 20, 2016


Right, but the article argues the "sea change" was driven by predation and oxygen, not by new forms of cooperation.

Yes, obviously more cells are becoming more precisely differentiated during development, which does require more developmental signaling, which does enable further development. Yet, evolutionarily that's still exploiting the germ-line cooperation that already exists, not new forms of cooperation. And it didn't happen earlier because the need came from predation.

It's likely reasonable to discuss sexual selection as a new form of cooperation, but that's not discussed anywhere I've seen.
posted by jeffburdges at 12:49 PM on February 20, 2016 [1 favorite]


A Live Science article showing visitors, reefs, fossils.

Neoproterozoic successions "from a petroleum systems prospective". "These large mounded growths such as these (behind the geologist) are predicted to be major hydrocarbon reservoirs".
posted by Twang at 4:04 PM on February 20, 2016


Yeah. I'm later. Fish sex and eyeballs.

I read "Fish sex and eyeballs" and my brain immediately free-associated "and whiskers on kittens". Which has nice rhythm, but is not really correct for the Devonian. It did, however, indirectly lead me to this gem: Evolution song by Samin. I think it definitely deserves more than the 271 views it currently has.
posted by Kabanos at 5:19 PM on February 20, 2016 [3 favorites]


my brain immediately free-associated "and whiskers on kittens"

Because Metafilter loves The Sound of Music
posted by cynical pinnacle at 5:13 AM on February 21, 2016


Darwin - The Musical

That would so work. The Barnacle Dance alone...
posted by Devonian at 5:45 AM on February 21, 2016


It was bioturbation (a glorious word, and even better idea [made all the better for being so crucial to the development of intelligent life]). Bioturbation and the movement from 2d bottom dwelling sessile life to burrowing worms, and from there, the development of all sorts of new environments conducive to newly developing forms, new predator/prey interactions. The Cambrian Explosion is the end result of the Cambrian Substrate Revolution (sorry if the post is considered ugly [it was an experimental phase, the post was designed to model soil horizons at scale]). Bioturbation, the outcome of our wormy ancestors getting down. A topic of great small importance, indeed one of Darwin's greatest works, but I know not if it will interest you.
Around the start of the Cambrian, organisms began to burrow vertically, forming a great diversity of different fossilisable burrow forms as they penetrated the sediment for protection or to feed. These burrowing animals broke down the microbial mats, and thus allowed water and oxygen to penetrate a considerable distance below the surface. This restricted the sulfate-reducing bacteria and their H2S emissions to the deeper layers, making the upper layers of the sea-floor habitable for a much wider range of organisms. The upper level of the sea-floor became wetter and softer as it was constantly churned up by burrowers
-Quick Cambrian Substrate Revolution primer.

posted by infinite intimation at 4:15 AM on February 22, 2016 [2 favorites]


Thanks Infinite intimation, I had missed your earlier post.
posted by Kabanos at 7:21 AM on February 22, 2016


fish, sex and eyeballs

I've got a packet of chocolate hobnobs if you'd like to come round later, Devonian.
posted by glasseyes at 9:32 AM on February 22, 2016




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