Cambrian Explosion and Evolution

[Correa Neto]

In any discussion of this topic, the matter of what went before the Cambrian must be considered- particularly the extremes of climate often referred to as "Snowball Earth". If there were, as we now strongly suspect at least three periods of all but absolute global ice age in the late precambrian, we would expect to see rapid expansion after they ended into the range of new habitats formed.

As for further back- much further back- I suspect this is a question of improved technological identification of micro- and even nano-fossils, which I expect exist in abundance if we only knew what to look for.

Of course, the older rocks are, the more chance they have been metamorphosed at the sort of pressure and temperature that erases all fossil and mineralogical evidence of life, or even lifelike chemistry. But there are a lot of very old, low grade metamorphics. It's possible we will develop the ability to spot life signatures in these.

I think explosions are , like car chases, of interest to adolescents.

Grown ups prefer a good, slow, detective story.

You know, I've been developing some weird sort of fetish for Precambrian life... I am used to work with Eoproterozoic and late Archean rocks. Every now and then I find myself looking at carbonaceous slates and other thin-grained metasediments with very little deformation. Crap! Where are thou, oh early creepers?

Microscopic critters in BIF, stromatolites, yeah, check. Organic matter, check. Rocks and environments suitable for preservation, check. Macroscopic fossils? Nope. Trace fossils? Very few and at the younger stuff.

My two cents?
No large multicellular critters and/or only soft bodied critters. Soft bodied, jellyfish-like critters leave few if any traces behind. Late Proterozoic (or even older) seas could be teeming with giant jellyfishes, but the odds of finding a preserved impression are very very low. That's what I think when I look at a thick deep water turbiditic Proterozoic sequence, for example. But hey, I'll keep looking just in case. Maybe, one day... It would be a ticket to Nature!

 

[DC]

Do we know how long animals in the Cambrian explosion lived?

 

[Dinwar]

Currently, the thought is that the Cambrian fauna didn't live much past the Cambrian. That said, it's an open question as to whether this is true, or whether this is an artifact of a number of biases (volume of rock sampled, researcher interest, and a number of others). Also, we don't really have good constraints on this fauna yet--until 10-20 years ago most of these weird forms were singletons (we have one fossils of the species) or limited to a single locality. A few may well have lived into later periods, in environments which limit perservation potential or which preclude discovery (there's a theory that older taxa migrate into deeper water, and we only have good ocean crust records for the past 250 million years).

 

[DC]

Currently, the thought is that the Cambrian fauna didn't live much past the Cambrian. That said, it's an open question as to whether this is true, or whether this is an artifact of a number of biases (volume of rock sampled, researcher interest, and a number of others). Also, we don't really have good constraints on this fauna yet--until 10-20 years ago most of these weird forms were singletons (we have one fossils of the species) or limited to a single locality. A few may well have lived into later periods, in environments which limit perservation potential or which preclude discovery (there's a theory that older taxa migrate into deeper water, and we only have good ocean crust records for the past 250 million years).

no i meant how long it took from one generation to the next.

the shorter their lifespan the less spectacular is their "sudden" appearance.

i don't find the proper words i think.
but like with bacteria that replicate very fast, it is possible to observe them evolve. with chimpanzees that is not possible because they are living so long.

 

[Dinwar]

Oh! That makes sense.

I'd say a yearly life cycle for the small ones, and perhaps yearly mating but multi-year lifespans for the big ones, based on modern marine organisms. To be honest, though, I don't think we'll ever know--paleonotlogy is really bad at answering those questions. Just look at the debate over T. rex ages, and we actually know what phylum, class, order, etc. those things belong in, and have modern analogs!

 

[DC]

Oh! That makes sense.

I'd say a yearly life cycle for the small ones, and perhaps yearly mating but multi-year lifespans for the big ones, based on modern marine organisms. To be honest, though, I don't think we'll ever know--paleonotlogy is really bad at answering those questions. Just look at the debate over T. rex ages, and we actually know what phylum, class, order, etc. those things belong in, and have modern analogs!

thanks