NEET BIOLOGY

Detailed explanation-1: -At five other times in the past, rates of extinction have soared. These are called mass extinctions, when huge numbers of species disappear in a relatively short period of time. Paleontologists know about these extinctions from remains of organisms with durable skeletons that fossilized.

Detailed explanation-2: -Mass extinctions-when at least half of all species die out in a relatively short time-have occurred only a handful of times over the course of our planet’s history. The largest mass extinction event happened around 250 million years ago, when perhaps 95 percent of all species went extinct.

Detailed explanation-3: -Based on evidence in the fossil record, scientists have identified major extinction events at the end of these geologic periods: Cretaceous Period-66 million years ago. Triassic Period-201 million years ago. Permian Period-252 million years ago.

Detailed explanation-4: -Although the best-known cause of a mass extinction is the asteroid impact that killed off the non-avian dinosaurs, in fact, volcanic activity seems to have wreaked much more havoc on Earth’s biota. Volcanic activity is implicated in at least four mass extinctions, while an asteroid is a suspect in just one.

Detailed explanation-5: -To explain what caused this mass extinction, scientists have focused on events that would have altered our planet’s climate in dramatic, powerful ways. The leading theory is that a huge asteroid or comet slammed into Earth 65 million years ago, blocking sunlight, changing the climate and setting off global wildfires.