The first mass extinction is the Ordovician mass extinction and it happened about four hundred and forty million years ago. This mass extinction occurred during the Paleozoic Era. The mass extinction affected up to 85 percent of the living species at that time. It was assumed based on discoveries that continental drift and subsequent climate change caused the Ordovician mass extinction. It occurred in two separate waves.
This is the second major mass extinction which happened during the Paleozoic Era. It occurred around three hundred and seventy-five million years ago and it excluded 80 percent of the species that were alive during that period. The causes of the second of mass extinction are a reduced level of oxygen in the oceans, rapid cooling of air temperature and volcanic eruptions or meteor strikes. A lot of plants lived on the land prior to that period which leads to a decrease in a level of oxygen for species living in the sea. This also affected the amount of carbon dioxide in the atmosphere which created a problem of adaptation for land species.
This is the third major mass extinction that occurred about two hundred and fifty million years ago. The extinction covered around 96 percent of the living species in the world during that time. The real cause of this mass extinction is unknown but it was suggested that asteroid strikes, volcanic eruption, microorganisms and climatic variation caused the third mass extinction. Permian mass extinction is the biggest mass extinction that nearly eliminated all the living organisms on the earth.
This is the fourth mass extinction and it ensued at the end of the Triassic era of the Mesozoic period about two hundred million years ago. This mass extinction affected around 50 percent of the living species during that period. Triassic-Jurassic Mass Extinction was caused by volcanic eruption, climate change, frequent change of the sea levels and pH. Volcanic activity was the major cause of the fourth mass extinction. Gases were emitted into the atmosphere leading to unfavorable conditions for the living species.
The fifth major mass extinction occurred about sixty-five million years ago, at the end of the Cretaceous period of the Mesozoic era. This mass extinction affected approximately 75 percent of the species during that period. It was caused by a serious asteroid or meteor influence. The fifth extinction is well-known as the mass extinction that leads to the death of all the dinosaur on earth. The asteroid impact affected the climate which made life miserable for the living species.
Consequently, Scientists suspects that we are presently living through the 6th mass. Numerous well-known species have been lost since humans have advanced. Since mass extinction happenings can take millions of years, it is likely we are observing the sixth major mass extinction event.