6th Mass Extinction: Subject: Environment Section: Conservation Mass Extinction Time Period Size of extinction Cause of Extinction 1stMass Extinction-The Ordovician Mass Extinction The Ordovician Period of the Paleozoic Era (about 440 million years ago) Up to 85% of all living species eliminated  Continental drift and subsequent climate change 2ndMass Extinction-Devonian Mass Extinction The Devonian Period […]