Mass Extinction: Five mass extinction events have shaped Earth’s history, and the sixth is ongoing while we are here. What defines a mass extinction is the death of about three quarters of all existing species in a short time – around 2.8 million years, according to The Conversation. The previous mass extinctions are the scientific references that we are creating the conditions for a 6th event.
Research done in the last decade indicated that, during the 20th century, vertebrate species died up to 114 times faster than they would without human activity, since animals extinct in 100 years would have taken 11,400 years to become extinct with the rates natural. The study revealed that a large part of this is due to human activities that lead to an environmental imbalance, causing pollution, loss of habitat, introduction of invasive species and increased carbon emissions, which drive climate change.
During the 20th century, more than 540 terrestrial vertebrates were extinct. From 1970 until today, populations of vertebrate species have decreased by an average of 68%. Currently, more than 35 thousand species are threatened with extinction.
Extinction of the Ordovician-Silurian
It occurred 440 million years ago and extinguished marine organisms. About 85% of the existing species have been decimated. The cause was a severe climate change that altered the sea temperature, causing the death of most of the lives in the ocean. There was also the glaciation – a period of intense cold – of the supercontinent Gondwana, which ended up drastically reducing the water level of the seas, causing loss of habitat for many species and destroying the food chain of others.
Some alternative theories suggest that toxic metal may have dissolved in ocean waters during a period of oxygen depletion, which ended up wiping out marine life at the time.