Three of the five big mass extinctions that science believes occurred on Earth:
End Ordovician, 444 million years ago, 86% of species lost
Graptolites, like most Ordovician life, were sea creatures. They were filter-feeding animals and colony builders. Their demise over about a million years was probably caused by a short, severe ice age that lowered sea levels, possibly triggered by the uplift of the Appalachians. The newly exposed silicate rock [is believed to have] sucked CO2 out of the atmosphere, chilling the planet.
My edits in brackets. Note the use of "was probably caused". No edit needed there. What caused the short ice age? Just curious. Also note that CO2 was believed to have been removed from the atmosphere.
Mama Earth is a b*tch, eh?
Late Devonian, 375 million years ago, 75% of species lost
Trilobites were the most diverse and abundant of the animals that appeared in the Cambrian explosion 550 million years ago. Their great success was helped by their spiky armour and multifaceted eyes. They survived the first great extinction but were nearly wiped out in the second. The likely culprit was the newly evolved land plants that emerged, covering the planet during the Devonian period. Their deep roots [may have] stirred up the earth, releasing nutrients into the ocean. This might have triggered algal blooms which sucked oxygen out of the water, suffocating bottom dwellers like the trilobites.
Wow, and no one was there fertilizing their lawns, 'cuz I heard algae blooms are my fault. Moving along.....
End Permian, 251 million years ago, 96% of species lost
Known as “the great dying”, this was by far the worst extinction event ever seen; it nearly ended life on Earth. The tabulate corals were lost in this period – today’s corals are an entirely different group. What caused it? A perfect storm of natural catastrophes. A cataclysmic eruption near Siberia [is believed to have] blasted CO2 into the atmosphere. Methanogenic bacteria [may have] responded by belching out methane, a potent greenhouse gas. Global temperatures [are believed to have] surged while oceans acidified and stagnated, belching poisonous hydrogen sulfide. “It set life back 300 million years,” says Schmidt. Rocks after this period record no coral reefs or coal deposits.
Mama Earth has real power doesn't she? She can giveth CO2 and taketh it away (toss in methane and sulfur dioxide while we're at it). You and your cars and cows - PFFFFT!!!
As for the other two:
End Triassic, 200 million years ago, 80% of species lost
Of all the great extinctions, the one that ended the Triassic is the most enigmatic. No clear cause has been found.
Science, where are you?
End Cretaceous, 66 million years ago, 76% of all species lost
Volcanic activity and the asteroid impact that [are believed to have] ended the dinosaurs’ reign provided the final blow.
And you think you're something don't you, puny human with your cell phone? The not caveman high technology know-it-all. I laugh at your primate hubris. You weren't around for any of the real action.
And what's missing from these analyses? Any sun spot activity data in there? I hear a lack of sun spots, or an abundance can cause real trouble. But what do I know? I'm just a guy with an opinion.