Читать книгу Geology For Dummies - Alecia M. Spooner - Страница 58

Long after the first life forms existed, Earth experienced periods when many different species thrived, filling the oceans and eventually the land. At least five times in Earth’s long history, thousands of species were wiped out in a very short time. (Geologically speaking, a “short time” can span a few million years; I explain geologic time in Chapter 16.) Such events are called mass extinctions.

Even if you haven’t heard about the other extinctions, you likely know about the extinction of the dinosaurs. But the extinction of the dinosaurs was not the largest mass extinction event in Earth’s history. Hundreds of millions of years before the dinosaurs, an extinction took place that killed 80 percent of all the plant and animal groups existing at the time.

In Chapter 22, I describe what is currently known about the mass extinctions in Earth’s past. However, geologists and paleontologists (people who study fossils) have many unanswered questions about how and why these periods of major extinction occurred. Some propose changes in climate as the culprit, and others point to meteor impacts or extreme volcanic activity. Still others claim only a combination of all these factors could have led to such dramatic mass extinctions.