Extinction event

Sometimes many living things die out.

This happens very fast. It can happen to plants and animals. This is called an extinction event.

Earth has had five big events. These events changed life on our world. One big event happened to dinosaurs. They are all gone now.

Some events happen because of the water. For example, things in the sea can lose the air they need.

Today, some people say a new event is starting. This is because of things people do. We must learn how to help our world.

An extinction event is a time when many living things die out. This happens very fast. It is much faster than the normal way life changes.

Scientists often talk about the "Big Five." These are the five largest events in Earth's history.

One event happened in the ocean. It is called the Late Ordovician extinction. Some studies say it was caused by global warming. Other studies say it was caused by the world getting cold.

Another event happened in the Late Devonian. This time, nutrients flowed into the sea through rivers. This caused algae to grow very fast. When the algae died, they used up the oxygen in the water. This made it hard for sea life to breathe.

The largest event is called the "Great Dying." It happened during the Permian-Triassic period. It wiped out many groups of animals. It even wiped out all the trilobites.

The most famous event is the Cretaceous-Paleogene extinction. This event killed all non-avian dinosaurs. It left more room for mammals and birds to grow.

Today, some say a sixth event is starting. This is because of human activity. Many plants and animals are now at risk.

An extinction event is a time when many living things disappear very quickly. This is much faster than the normal rate at which new species appear. Scientists call this a mass extinction or a biotic crisis. It happens when the number of different living things drops sharply.

These events are important because they change the course of life on Earth. They create new paths for the survivors to follow.

These events work by changing the world's environment very suddenly. For example, during the Late Devonian extinction, nutrients flowed into oceans through rivers. This caused massive algal blooms, which are large growths of algae. When the algae died and rotted, they used up the oxygen in the water.

Without oxygen, many sea animals could not survive. Other events were caused by things like global warming or volcanic ash.

In 1982, scientists Jack Sepkoski and David M. Raup studied these patterns. They identified five major periods where life lost a huge amount of variety. These are often called the "Big Five."

They found these events by looking at trends in the fossil record. While they originally tracked absolute numbers, later studies looked at the proportion of life lost. This helped scientists understand how severe each event really was.

History shows many different levels of these events. The Late Ordovician extinction killed 85% of all species. The "Great Dying" at the Permian-Triassic boundary was the largest. It wiped out 84% of marine genera and 70% of land vertebrates.

The Triassic-Jurassic event left dinosaurs with less competition. Finally, the Cretaceous-Paleogene extinction killed all non-avian dinosaurs.

This allowed mammals and birds to become the main animals on land.

We can see how these events link to the world today. Scientists believe a sixth mass extinction is happening right now. This is due to human activities like using too many natural resources.

Research shows extinctions have happened 1,000 times faster since 1900 than normal. About 1 million species are currently threatened with extinction. Understanding the past helps us see how much our actions matter for the future.

An extinction event is a period of rapid and widespread loss of biodiversity on Earth. Scientists also refer to these events as mass extinctions or biotic crises. These events occur when the rate of species disappearing exceeds the rate of speciation, which is the process of new species forming. A mass extinction is specifically identified by a sharp decline in the abundance and variety of multicellular organisms. While some species go extinct all the time, this is known as the background extinction rate. A mass extinction event represents a sudden spike far above that normal level.

The mechanics of these events often involve sudden changes to the global environment. For instance, during the Late Devonian extinction, nutrients were carried into the oceans by rivers. This process triggered massive algal blooms, where algae grew in huge quantities. As this algae died and decomposed, it consumed the dissolved oxygen in the water column. This created anoxic conditions, meaning the water lacked enough oxygen for life. Other events have been linked to volcanic activity, global warming, or changes in atmospheric carbon dioxide.

Scientists Jack Sepkoski and David M. Raup published a landmark paper in 1982. They identified five specific geological intervals that experienced excessive loss of diversity. These are commonly known as the "Big Five" mass extinctions. Originally, these periods appeared as outliers on a trend of decreasing extinction rates during the Phanerozoic Eon. As researchers applied more stringent statistical tests to fossil data, these five events were confirmed. These events are not necessarily separate incidents but may exist on a smooth continuum of extinction events.

The first major event was the Late Ordovician mass extinction, occurring 445 to 444 million years ago. This event killed 27% of all families, 57% of all genera, and 85% of all species. Some studies suggest volcanism caused global warming and anoxia, while others suggest cooling and glaciation were the drivers. The second was the Late Devonian extinction, occurring between 372 and 359 million years ago. This was actually a series of events, including the Kellwasser Event and the Hangenberg Event. Together, they eliminated 19% of families, 50% of genera, and at least 70% of species.

The third and largest event was the Permian–Triassic extinction, often called the "Great Dying." Occurring 252 million years ago, it wiped out 53% of marine families and 84% of marine genera. It also claimed about 81% of all marine species and 70% of terrestrial vertebrate species. This event was so massive it ended the dominance of early synapsids on land. In the oceans, the percentage of sessile animals, which are organisms unable to move, dropped from 67% to 50%. This massive loss of life created vacant niches that allowed archosaurs to eventually become dominant.

The fourth event was the Triassic–Jurassic extinction 201.3 million years ago. This event resulted in the loss of 23% of families and 48% of genera. It eliminated many large amphibians and archosauromorphs. This reduction in competition allowed dinosaurs to become the primary animals on land. The fifth and final "Big Five" event was the Cretaceous–Paleogene extinction, or K–Pg extinction. This event killed 17% of families, 50% of genera, and 75% of all species. It famously caused the extinction of all non-avian dinosaurs and many marine groups like ammonites and mosasaurs.

Understanding these patterns is vital because scientists believe a sixth mass extinction is currently underway. This modern event is driven by human activities, including population growth and the overconsumption of natural resources. Since 1900, extinction rates have occurred at over 1,000 times the background rate. A 2023 study showed that at least 73 genera of animals have gone extinct since 1500 due to human impact. Currently, an estimated 1 million plant and animal species are threatened with extinction. Studying the fossil record helps us understand how these biological crises reshape the entire history of life.