Mass Extinctions

Table of Contents

What is Mass Extinction?

The fossil records show that something unusual happened millions of years ago. A wide range of animals from terrestrial megafauna to tiny aquatic beings died suddenly. This extinction of a large number of animals altogether is known as a mass extinction.

As the new species start evolving, the old species got depleted from the earth. More than 90% of the species are believed to have become extinct in the last 500 million years.

Mass extinctions are deadly events. The Permian Triassic extinction took place 250 million years ago. It gave rise to the era of dinosaurs. 96% of the marine species were depleted during the “Great Dying”. The fossils from the ancient seafloor depict the diversity of life at sea.

Also read: Evolution

Six Mass Extinctions

Ordovician-Silurian Extinction

During this extinction, the life of small aquatic organisms ended. This happened 440 million years ago. 60% of the animal species got extinct during this period.

Devonian Extinction

It marks the extinction of tropical marine life forms. It occurred 375 million years ago – 360 million years ago. 70% of the marine species including the coral reefs became extinct in the shallow areas of the sea.

Permian-Triassic Extinction

It is the largest mass extinction known which depleted a wide range of species, including vertebrates. This was an abrupt extinction. 96% of the marine and terrestrial animal species became extinct and therefore the event is known as the “Great Dying”. It is thought to be the result of a massive volcanic activity or a comet striking the surface of the earth.

Triassic-Jurassic Extinction

This took place 18 million years ago at the end of the Triassic age. All the terrestrial and marine reptiles and plant species including the dinosaurs were wiped out.

Cretaceous-Tertiary Extinction

This marks the extinction of nonavian dinosaurs. They were wiped out at the end of the Cretaceous period and the beginning of the Tertiary period. Hence called KT extinction. This marked the dawn of a new age. This extinction took place 65 million years ago when a massive asteroid hit the earth’s surface. This led to immense changes in the atmosphere, sea levels and temperatures that ended the life on earth.

Sixth Mass Extinction

We are currently in the middle of the sixth mass extinction, and humans are the major cause of it. Human beings are directly or indirectly responsible for the extinction of various species for personal benefit.

The invasive species were transported from one part of the world to the other which eliminated the native species. Also, the immigration and emigration of humans and animals have spread certain diseases in different parts of the world where they were never present before.

The chemicals have harmed marine life. Natural resources are depleting due to the growing population. Heavy pollution has led to an increase in temperatures and water levels in the sea which will have catastrophic effects on the life on earth in the near future.

Causes of Mass Extinctions

  • Changes in sea levels changed the salt and oxygen concentration in parts of the earth’s oceans. The change in sea levels disturbed their habitats which led to the extinction of species.

  • The meteorite attacks on the earth, anoxic conditions, volcanic activities all led to the extinction of a large mass of animals during the Permian-Triassic extinction. The meteorites had a catastrophic effect on the earth.

  • The increase in temperatures led to the melting of glaciers and an increase in the sea levels.

Also read: Evolution by Stages

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