[Biology Class Notes] on Mass Extinction Pdf for EXAM

About more than 99 percent of all the organisms that have ever lived on Earth are now extinct. As the newer species evolve to fit in the ever-changing ecological niches, the older species fade away. However, the rate of extinction is much far from the constant. About more than a couple of times in the last 500 million years, 75 per cent to more than 90 percent of all the species on Earth have been disappeared in the geological blink of an eye in several catastrophes that we call mass extinctions. Though the mass extinctions are deadly events, they help to open up the planet for the newer forms of life to emerge. The mass extinction that was studied the most, that remarked a boundary between the periods of Cretaceous and Paleogene around 66 million years ago, had killed the nonavian dinosaurs and eventually made space for the mammals and the birds to rapidly diversify and gradually evolve. In this article, we will discuss about the mass extinction, the sixth mass extinction, the mass extinction definition, and the mass extinction events.

5 Mass Extinctions

The 5 mass extinction events include the following:

1. The Ordovician – Silurian Extinction

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

2. The Devonian Extinction

This marks the extinction of the tropical marine life forms. This extinction occurred about 20 million years ago. 70% of the marine species which included the coral reefs were extinct in the shallow regions of the sea.

3. The Permian – Triassic Extinction

This is the largest mass extinction that is known that depleted a huge range of species, including the vertebrates. It was an abrupt extinction. 96% of the marine and the terrestrial animal species were extinct and hence this event is referred to as the Great Dying. It is known to be a result of a huge volcanic activity or the comet that struck the surface of the earth.

4. The Triassic – Jurassic Extinction

This extinction took place about 18 million years ago during the end of the Triassic age. All the terrestrial and marine reptiles and the plant species which included the dinosaurs were all wiped out.

5. The Cretaceous-Tertiary Extinction

This marked the extinction of the nonavian dinosaurs. They were all wiped out at the end of the Cretaceous period and during the beginning of the Tertiary period. Therefore, it is called the KT extinction. It marked the dawn of a new era and age. The extinction took place about 65 million years ago when a huge asteroid hit the surface of the earth. This, in turn, led to immense changes in the atmosphere, the sea levels and the temperatures that ended life on the surface of the earth.

Sixth Mass Extinction

We are at present in the middle of the sixth mass extinction, and humans are the big cause of it. The humans have already killed most of the several animal species for their own recreational activities and benefits.

The invasive species were previously transported from one part of the world to the other part that eliminated the native species that resided in that part. Also, the immigration and the emigration of the humans and the animals have spread several diseases in several different parts of the world wherein they were not present before.

The toxic chemicals have harmed marine life to a greater extent. The natural available resources are also depleting to a wider extent because of the growing population. The heavy pollution has led to an increase in the temperatures and the water levels in the sea that would have several catastrophic effects on life on the earth in the coming future.

Mass Extinction Causes

1. The changes in the sea levels have changed the salt and the oxygen concentration in different parts of the earth’s oceans. The changes in the sea levels have disturbed their habitats and that led to the extinction of several species.

2. The meteorite attacks that happened on the earth, the anoxic conditions, and the volcanic activities all led to the extinction of a huge mass of the animals in the Permian-Triassic extinction. The meteorites that have fallen on the earth had a catastrophic effect on the planet.

3. The increase in the temperatures had led to the melting of the glaciers and hence an increase in the sea levels.