It is too bad that so much evidence was lost due to oceanic plate subduction. A "day" geologically can be 10,000 years or an event of a short period with aftermath of centuries, like an impact. The time frame goes well with a very large ocean asteroid impact in the "Nemesis" time frame. Being near the middle now, it was 9 (26.3 million year) cycles ago, and the large sea bottom crater subducted and remelted into the upper mantle. It was the worst with 90% of species gone extinct. It is interesting that that is close to what is probable with the human caused AETM "event".
The group of cyanobacteria that created our oxygen atmosphere which killed most of them off . Here is an interesting take:http://io9.com/5853522/a-plausible-end+ ... thought-of
" You may not realize this, but for almost 2 billion years of the 4.5 billion year history of Earth, our planet's atmosphere was dominated by methane and other greenhouse gases. There was no free oxygen, and therefore no life as we know it could survive. But then, about 2.35 billion years ago, microbes called cyanobacteria — also known as blue-green algae — began to produce free oxygen as a byproduct of the photosynthesis process. The algae did this by breaking apart water molecules during their digestive process, freeing the O (oxygen) from H2O (water).
As a result, these cyanobacteria poisoned the world. At least, that's how it would have seemed to all the microbes around them, known as stromatolites, who breathed methane. Suddenly, all this oxygen was in the air and the stromatolites began to die out. Eventually the oxygen-based atmosphere allowed life as we know it (including humans) to evolve. Over the dead bodies of those methane-breathing stromatolites."
Actually, it killed most of the cyanobacteria, too, like how yeast kills itself. They ODed on their own waste.