How Many Mass Extinctions Have There Been On Earth? – BGR

Earth has a long and dramatic history, and one recurring theme is extinction. Did you know that over the last 500 million years, our planet experienced five major mass extinction events? These events are periods when life on Earth changed drastically. Thousands of species of animals, insects, and plants were wiped out. The causes varied from massive volcanic eruptions, asteroid impacts, and sudden climate shifts, but the outcome was always the same: life was pushed to the brink.

Many scientists believe we are living through a sixth mass extinction, but this time, the driver isn’t a super-volcano or massive asteroid. It’s human activity driving the climate crisis that sometimes even climate models can’t fully explain. Our own actions, such as deforestation, pollution, overfishing, and habitat destruction, are accelerating the rate at which species are disappearing.

Understanding the past five mass extinctions can help us make sense of what’s going on now. These ancient events show us how fragile life on Earth can be and how ecosystems respond to massive disruptions. They also teach us how long it can take nature to recover from such events, and what can be done to speed up the recovery process.

The first of the “Big Five” mass extinctions happened approximately 444 million years ago, during the late Ordovician period. At this time, life on Earth mostly consisted of ocean creatures such as trilobites, brachiopods, and corals. This event wiped out over 86% of existing species, making it one of the most devastating die-offs in the history of our planet.

The main culprit of the Late Ordovician mass extinction was a severe climate shift. The Earth cooled rapidly due to a severe drop in the carbon dioxide levels, which caused a brutal ice age. The southern hemisphere of the planet was covered in glaciers, causing the sea levels to fall. The shallow marine habitats, where the ocean life thrived, chemically changed, causing the death of many species. As if that wasn’t enough, when the ice eventually melted, sea levels rose again, putting even more stress on the ecosystem. While this event was a catastrophe for many marine species, it also cleared the way for new forms of life to evolve.

The Late Devonian mass extinction wasn’t a single, sudden, disastrous event. It was a period that lasted for millions of years, occurring approximately 372 million years ago. During the second mass extinction, around 75% of all life on Earth was lost. Again, marine life was hit hardest with the devastation of the coral reefs where life was most abundant. It took several million years for these ecosystems to recover.

One of the leading theories is that a massive growth of plant life on land played a crucial role in the Devonian extinction. As plants evolved and spread across the continents, their roots broke down the soil, releasing nutrients into the rivers and oceans. This may have caused massive algae blooms, which depleted all the oxygen in the water. Without oxygen, many species simply died off in a phenomenon known as anoxia. There are other factors involved in the Devonian extinction, but they’re still a bit of a mystery to modern science. They may have included volcanic eruptions, asteroid impacts, and climate change.

The Permian-Triassic extinction event was the most severe die-offs that happened in Earth’s history. It happened around 252 million years ago, and it wiped out 90-96% of all species. That’s why it’s also referred to as “The Great Dying.” A series of volcanic eruptions in Siberia triggered this climate catastrophe. These eruptions lasted for hundreds of thousands of years and released enormous amounts of greenhouse gases into the atmosphere. They triggered global warming, the acidification of oceans, and the drop in oxygen levels in the seas.

Life on Earth couldn’t cope with these conditions. The oceans became nearly lifeless, the forests disappeared, and entire groups of animals went extinct. Marine life and insects were hit hardest, but also some of the vertebrates, such as pelycosaurs, were completely extinct by the end of the Permian era. The die-off continued for about 30,000 years. The Permian-Triassic extinction shows us how environmental changes can easily push life past the tipping point.

The Triassic-Jurassic extinction happened around 201 million years ago, marking the end of the Triassic period, and clearing the stage for the rise of the dinosaurs in the Jurassic. About 70-76% of all species were wiped out, mainly in the oceans, and among early land reptiles and plants. The most likely cause of the fourth mass extinction is another volcanic activity, this time in the Central Atlantic Magmatic Province. The huge amounts of carbon dioxide were released into the atmosphere, which led to the sharp spike in global temperatures and ocean acidification.

Although this period of climate instability was devastating for many species, dinosaurs and some mammals survived and continued to thrive. Since many of their competitors were gone, they had room to diversify and dominate the land ecosystems for the next 135 million years. The Triassic-Jurassic extinction highlights how climate upheaval can reshape life on Earth. While some groups failed to cope with the oncoming changes in their ecosystems, other species managed to adapt and even thrive.

The Cretaceous-Paleogene extinction event is probably the most famous one. It happened around 66 million years ago and it wiped out the dinosaurs (except for avian dinosaurs that evolved into today’s birds). In total, 75% of species disappeared, including reptiles, mammals, plants, and entire groups of various animals.

The main cause of the fifth and last mass extinction was a massive asteroid that originated beyond Jupiter and crashed into what is today the Yucatan Peninsula in Mexico. It was around 10 to 15 kilometers wide, and it created the famous Chicxulub crater. The impact of such an asteroid created unimaginable destruction. It was followed by intense heat, tsunamis, wildfires, and a nuclear winter created by the ash, dust, and debris that was so dense it blocked the sunlight. This sudden global darkness created a rapid drop in temperatures, disrupting photosynthesis. The result was massive alterations to the food chain both, on land and in the oceans, which gave us fruits like grapes among other things. Some scientists believe that aside from the asteroid, massive volcanic eruptions in India occurred, contributing to the mass extinction.