After 65 million years, the Earth has again entered a mass extinction period. BBC reports that in a study based on fossil records, scientists found out that within more than 100 years, the extinction of vertebrate animals are over 100 times higher as compared to previous records.

"We are now entering the sixth great mass extinction event," said an author of the study.

According to the new study which was collaborated on by researchers from Berkeley, Princeton and Stanford universities, 400 more vertebrates have disappeared since 1900. Previously, this rapid extinction would usually take up to 10,000 years.

Published in the Sciences Advances Journal, this "dramatic decay of biodiversity" is caused by deforestation, pollution, and climate change, the study concluded.

"If it is allowed to continue, life would take many millions of years to recover and our species itself would likely disappear early on," according to the study's lead author, Gerardo Ceballos.

Scientists suggest immediate action and intensive conservation is needed in preventing the Earth's sixth massive extinction.

"Avoiding a true sixth mass extinction will require rapid, greatly intensified efforts to conserve already threatened species, and to alleviate pressures on their populations - notably habitat loss, over-exploitation for economic gain and climate change," Researcher Professor Paul Ehrlich at the Stanford Woods Institute for the Environment told Huffington Post.

"Our calculations very likely underestimate the severity of the extinction crisis. There are examples of species all over the world that are essentially the walking dead," he added.

The Earth's five massive extinction periods are the Ordovician-Silurian mass extinction, the Permian mass extinction, the Late Devonian mass extinction, the Triassic-Jurassic mass extinction, and the Cretaceous-Tertiary mass extinction. Reasons of these extinctions include drying out of waters, climate change, flood basalt eruptions and asteroid impacts.

The latest was the Cretaceous-Tertiary mass extinction which happened 65 million years ago, when a meteorite hit the Earth and caused the popular death of dinosaurs.