The Earth is witnessing its sixth mass extinction. Wildlife is disappearing at an alarming rate even as the phenomenon is a threat to our existence. What is even more shocking is that human activity is contributing to this extinction. Till now, five such mass extinctions had taken place. The last one occurred 66 million years ago and led to the extinction of dinosaurs. The likely causes of each of these extinctions may be different but had wiped out over 90 percent of organisms on Earth. The mass extinctions, known as biggest die-offs, show up in fossil records, according to an AFP report. The five mass extinctions are called Ordovician extinction, Devonian extinction, Permian extinction, Triassic extinction and Cretaceous extinction.
Ordovician extinction happened about 445 million years ago. It accounted for loss of 60-70 percent of species. According to reports, intense ice age led to planet-wide formation of glaciers that froze much of the world’s water, causing sea levels to fall sharply. Since most life at this time was in the oceans, all suffered.
Devonian extinction had taken place about 375-360 million years ago during which 75 percent of Species lost. Depletion of Oxygen in the Ocean led to the extinction of species.
95 percent of species wiped out during Permian extinction which had occurred about 252 million years ago. Asteroid impact and volcanic activity were the likely causes behind this. This is known as the mother of all extinctions, the “Great Dying”. It had caused havoc to the ocean and land life.
Triassic extinction took place about 200 million years ago and led to loss of 70-80 percent of species lost. There are debates over the plausible causes. One theory says a massive global warming took place due to massive lava eruptions. Other scientists blamed asteroid strikes, the AFP report states.
The last one- Cretaceous extinction happened about 66 million years ago. Dinosaurs were among 75 percent wiped out. Scientists believe that asteroid strike could have caused it, as per AFP report.