There have been five mass extinctions, roughly 50-150 million years apart due to various reasons (meteor strike, gamma ray burst, climate change, pollution). Technically we are in a 6th due to human behavior, but my question is the cambrian explosion and start of the Phanerozoic era was 542 million years ago, and the five (or six) mass extinctions only cover this period.
So does earth routinely undergo events every 50-150 million years that would cause mass death among multi-cellular life, but because we only had single celled life until ~600 million years ago, either the extinction events had no impact or their impact cannot be traced/studied because it affected single celled life?
I believe due to changes in the sun, multi-cellular land based life only has a 2 billion or so year window to exist on earth. I think we are somewhere in the middle of that window and other than that I think it is just single celled and/or ocean based life.