Earth's 5 catastrophic mass extinctions, explained
While life on Earth does usually find a way, it is not without some intense past–and future–periods of mass death. Extinction is not exclusive to dinosaurs. Our planet has gone through at least five periods of mass extinction, with the planet likely in a sixth wave of mass extinction–this one, driven by humans.
Our planet's first known mass extinction happened about 440 million years ago. Species diversity on Earth had been increasing over a period of roughly 30 million years, but that would come to a halt as water began to freeze in a massive ice cap towards the south pole.
The formation of the Appalachian Mountains was the potential cause of this cooling. When the supercontinent Gondwanaland collided with what is now North America, the ancient lapetus Ocean closed over a period of about 150 million years. The weathering of the freshly uplifted rocks from this continental collision may have sucked carbon dioxide out of the atmosphere. As a result, the planet drastically cooled, sea levels plummeted, and roughly 85 percent of species were wiped out.
Due to this drop in sea levels, it was particularly hard on marine species including brachiopods, corals, and trilobites.
Earth's marine species, especially those at the tropics, were in trouble again about 419 million to 365 million years ago. This series of mass extinctions during the Devonian period eventually eliminated about 75 percent of life. However, some of Earth's oldest fish called coelacanths make it out unscathed.
There was likely not a single definitive cause of this period of mass extinctions, but oxygen levels in the ocean continually dropped at this time. A combination of several major stresses including excessive sedimentation, rapid global warming or cooling, impacts from comets or meteorites, volcanic activity, or massive nutrient runoff from the continents may have caused these pulses of extinction.
[Related: The 'living fossil' that thrived during a mass extinction.]
Interestingly, plants on land may have played a role. Some of the plants had adaptations including using the stem-strengthening compound lignin and a vascular structure. Both traits allowed them to grow and for their root systems to go deeper than they had before. As a result of these deeper roots, rock weathering may have increased.
Earth's largest mass extinction, often referred to as the 'Great Dying,' occurred about 252 million years ago. Massive volcanic eruptions triggered catastrophic climate changes that altered the planet's entire biosphere. Over roughly 60,000 years, 96 percent of Earth's marine species and about three of every four land species were wiped out. Unfortunately, the Great Dying is the extinction event that most closely parallels Earth's current environmental crisis.
'Both involve global warming related to the release of greenhouse gasses, driven by volcanoes in the Permian and human actions currently,' paleontologist Christian Kammerer told Popular Science in a 2023 interview. '[They] represent a very rare case of rapid shifts between icehouse and hothouse Earth. So, the turmoil we observe in late Permian ecosystems, with whole sections of the food web being lost, represents a preview for our world if we don't change things fast.'
Yet, some species managed to survive. A group of primitive amphibians called the temnospondyls may have gotten by through feeding on freshwater prey that larger land-based predators couldn't get to. It also helped that they weren't picky eaters.
Life began to rapidly diversify after the Great Dying, but it still struggled. Large volcanic eruptions triggered the Triassic-Jurassic Extinction about 201 million years ago. Carbon dioxide levels rose yet again, acidifying the oceans and warming Earth by an average of five to 11 degrees Fahrenheit.
As a result, up to 80 percent of all terrestrial and marine species went extinct. Crocodilians were much larger and more diverse than they are today. They were also dominant terrestrial species, but most of them died out.
Both the Great Dying and Triassic-Jurassic extinctions ultimately paved the way for dinosaurs to dominate Earth. And we know how that went.
About 66 million years ago, a large space rock slammed into the Earth off the coast of the present-day Yucatán Peninsula of Mexico. The impact from this almost seven-mile wide asteroid generated huge tsunamis and plumes of dust, debris, and sulfur being hurled up into the atmosphere. All of this excess material brought on severe global cooling, while wildfires ignited within 900 miles of the impact. The crater formed by the asteroid strike was about 120-miles wide.
[Related: June was probably a terrible month to be a dinosaur. Here's how we know.]
As ecosystems collapsed, roughly 75 percent of all the existing plant and animal species went extinct. All non-avian dinosaur species were wiped out in what is arguably the most famous mass extinction in Earth's history.
With most dinosaurs gone, mammals diversified and took over, paving the way for the ecosystem we see today.
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