Yesterday I watched "An Inconvenient truth", Al Gore's award winning documentary. I have wanted to watch it since 2006, and for reasons I can't explain, I finally did it seven years later. If you have not watched it I strongly implore that you do it.
Now the title of this post may strike you as odd and not related to what you are reading. Let me explain. If you are having difficulties remembering the sequence of geological time scale- use the title as a mnemonic for aid.
Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous, Palaeocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, Holocene.
Among these periods five saw some major extinctions and rest some minor extinctions. The major extinctions were Ordovician (440 million years ago), Devonian (365 million years ago) both these carnages resulted in about 85 percent of species disappearing. The Triassic (210 million years ago) and Cretaceous (65 million years ago) swept clean about 75 % of the species. The best is for the last, Permian extinction (245 million years ago) wiped clean about 95% of the life on earth. Some of the prime contributors to this carnage were- Global warming, Global cooling, Changing sea level, Oxygen depletion of the seas, epidemics, meteor and comet impacts, runaway hurricanes ( hypercanes), massive volcanic eruptions and massive solar flares. Well coming back to Al Gores documentary that I mentioned above- It says our relentless Carbon-di-oxide pumping can cause five of the above mentioned contributors to recur. Each one of them nearly annihilated the earth; just imagine what all five can do. History does repeat itself.