Earlier today Senior Scientist at the Geoscience Research Institute Tim Standish responded to my question regarding a recent claim that life from 3.95 billion years ago was spotted in Newfoundland. I wrote to ask, On a practical basis, how did these earliest organisms even stay alive?
Rob Sheldon writes to defend the idea, at least in principle, if very primitive life forms arrived on comets bombarding Earth:
There is one type of life that can survive in a bath of water, sunlight, carbondioxide and nitrogen. That is to say, without any other life forms or sources of organic material or dissolved nitrate. It’s cyanobacteria, and some of the most common forms, are also the smallest.
These organisms have the ability to both photosynthesize and fix nitrogen. They can grow in completely pristine, sterile environments lacking all soluble nitrates or organics. Chemolithotrophs don’t even need sunlight, drawing their energy from chemical sources such as the oxidation of sulfur–but generally speaking, oxygen wasn’t available until photosynthetic life had made it. So probably cyanobacteria were the original pioneers.
Procholorococcus, at 0.5 to 0.7 μm in diameter, is the smallest known organism that photosynthesizes.
When the Earth cooled off, and when comets had deposited water, around 3.85 billion years ago, the Earth was ripe for colonization by these organisms. Therefore it should not be surprising to find that extinct comets which impact the earth (carbonaceous chondrites) have fossils of cyanobacteria. We know they are ancient because the proteins had long since hydrolyzed, and even the unstable amino acids had decayed away leaving behind only the 8 most stable amino acids suggesting dates > 400Myr.
Colonization would then explain why life appeared no more than 100 Myr after the oceans formed, perhaps within 50 Myr. In reality, this limit has error bars the same size as the limit, because we cannot really tell if there were a pause at all between the oceans forming and the life spreading. Geologically they were simultaneous, giving no time at all for evolution. But then evolution cannot explain the Origin-of-Life anyway, so even 1 billion years is too short for OOL, much less 50 Myr. The old anecdote of Wald that “time is in fact the hero of the plot” proves false, for time is the evil villain, pulling out the rug from under us.
The way the origin of life is being pushed back deep into the lava, it seems as if an extraterrestrial origin is the only alternative to spontaneous generation/creation.
It’s fun living in interesting times, no?
See also: But could there really be life at Earth’s molten rock stage? (Tim Standish)
Researchers: Evidence of life 3.95 billion years ago