I got talking with a geology student recently, and we could not help not bringing up one of the subjects that bring together biology and geology: mass extinctions. So here is some information in case you ever need to impress a geology student, or plan the next extinction.

There have been 6 mass extinctions. The 5 recent ones involved multicellular life. I count them as 6 because there was an earlier major one involving the production of oxygen. Yes, oxygen was not on Earth since the beginning.

This is all relevant to the snowball earth theory, the idea that the Earth was completely covered by ice in the past. Turns out it might have happened during the mass atmospheric oxygenation event, but there are also other possible dates, all before multicellular organisms evolved. Here is plenty of information about it, a bit long but the visuals on the Earth periods over time along are worth the visit.

If you can survive more reading, here is the wikipedia page on the mass extinctions, where the mass oxygenation is not considered a mass extinction.