Could Multicellular Life Evolve Sans Cryogenian?
Prior to the Cambrian, there have been three separate ice ages--the Huronian, from 2.4 to 2.1 billion years ago; and the two Cryogenian ice ages, from 720 to 635 million years ago, split in such by a ten-million-year lull.
Post-Huronian came the first eukaryotes, cells with a nucleus concealed within membranes. The first of some of the multicellular eukaryotes, the animals, first appeared 665 million years ago, near the last legs of the Cryogenian... or did they? I ask that because one of the evidence questioning the occurrence of the Cambrian "Explosion" is the fact that trilobites, the most iconic organisms of the Palaeozoic Era, were already diverse by the time it allegedly happened, which would indicate that they evolved much earlier, at least 700 million years ago.
The fact that eukaryotes evolved in the wake of the Huronian was no problem. As this BBC site may indicate, isolation by ice may force the cells to be more specialized. But what does not make sense for me was that melting such a global snowball, as the Huronian essentially was, meant an increase not just of nutrients dumped into the oceans, but also free oxygen rising into the atmosphere, yet animals did not come into the stage until the Late Cryogenian, in which the melting did the exact same thing the melting of the Huronian did.
So my question was - Could multicellular life evolve with just the Huronian glaciations and not the two Cryogenian glaciations?
This post was sourced from https://worldbuilding.stackexchange.com/q/136291. It is licensed under CC BY-SA 4.0.
1 answer
The earliest Metazoa originate between 800mya and 750mya, so anywhere from 80my to 30my prior to the beginning of the Cryogenian.
The occurrence of snowball periods is likely not a factor in their appearance. In fact, it has been suggested that the Cryogenian caused a loss of diverity in the Earth's oceans. This loss was not recovered until the glaciation ended, and the evolution of the Ediacaran fauna occurred.
My conclusion, therefore, is that the Cryogenian was not required for the evolution of animal life on Earth, and may have in fact inhibited it.
0 comment threads
0 comment threads