Life on our planet has experienced multiple mass extinctions over its 4.5 billion years. Scientists have seen evidence of at least five major episodes that eradicated organisms large and small. And many experts argue that the Anthropocene, the current era in which human activity is transforming the planet, is responsible for one in six.
Paleontologists track mass extinctions by studying rock samples from different eras. An extinction event has been detected when a large number of species that were abundant in the early fossil record reach a point where they become rare. Each of the five major extinction events wiped out more than 70 percent of all life on Earth at the time, the deadliest of which was the Permian-Triassic extinction about 252 million years ago, which probably wiped out more than 90 percent. It’s possible.
The causes of these extinctions are still debated, but scientists believe that most of them were caused by massive volcanic activity, the opening of huge cracks in the Earth’s surface that occurred over thousands or even millions of years. It is believed that this was caused by lava erupting over the area. This volcanic activity likely caused many other changes that directly led to extinction, such as ocean anoxia and starvation as a result of ocean warming. Ozone layer depletion caused by volatile substances released by volcanic activity. and wildfires caused by warmer weather.
About supporting science journalism
If you enjoyed this article, please consider supporting our award-winning journalism. Currently subscribing. By subscribing, you help ensure future generations of influential stories about the discoveries and ideas that shape the world today.
By studying the geological past, we can also learn about the present, says David Bond, a mass extinction expert at the University of Hull in the UK. “We must learn lessons from these events and use them to understand the potential impending diversity crisis.”
Triggers and kill mechanisms
Some of the causes listed here (such as volcanic activity and sea level change) are not necessarily the primary mortality mechanisms themselves. For example, an asteroid is not the actual cause of death for anyone other than the individuals directly impacted. Rather, it causes widespread and deadly conditions such as oxygen deficiency and acidification.
Rick Simonson. David Bond/University of Hull (science critic)
scale and casualties
Each of the five mass extinction events is characterized by the extinction of 70 percent or more of the species living at the time. Some groups disappeared completely, while others experienced significant declines.
Rick Simonson. David Bond/University of Hull (science critic)
