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.
The 5 mass extinction events include the following:
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.
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.
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.
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.
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.
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.
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.
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.
The increase in the temperatures had led to the melting of the glaciers and hence an increase in the sea levels.
1. What is mass extinction?
The fossil records predict that something unusual happened on earth several millions of years ago. A huge range of animals from the terrestrial megafauna to the tiny aquatic beings had died suddenly. This extinction of a larger number of animals together is called as the mass extinction.
As the new species start to evolve, the older species tend to get depleted from the surface of the earth. More than 90% of the total available species are known to have gone extinct in the past 500 million years.
Mass extinctions are known to be deadly events. The Permian Triassic extinction had taken place about 250 million years ago. It had given rise to the era of the dinosaurs. About 96% of the marine species had depleted during the Great Dying period. The fossils collected from the ancient seafloor depicted about the diversity of life at the sea.
2. What are the types of mass extinction?
The different mass extinctions on Earth includes the following:
End-Ordovician, about 443 million years ago
A severe ice age had led to the sea level falling by 100m, that wiped out about 60-70% of all the species that were prominently the ocean dwellers at the time. Later once the ice was melted, it left the oceans being deprived of oxygen.
Late Devonian, about 360 million years ago
A messy and prolonged climate change event yet again hit life in the shallow seas very hard and killed about 70% of the species which included almost all the corals.
Permian-Triassic, about 250 million years ago
This was the big one with more than 95% of the species being perished, which included the trilobites and the giant insects. This is strongly linked to the massive volcanic eruptions that occurred in Siberia that caused a huge episode of global warming.
Triassic-Jurassic, about 200 million years ago
Three-quarters of the species were again lost, most likely because of another great outburst of the volcanism. It left the Earth totally clear for the dinosaurs to flourish.
Cretaceous-Tertiary, about 65 million years ago
A giant asteroid impact on Mexico, immediately after the large volcanic eruptions in what is presently India, had seen the end of the dinosaurs and the ammonites. Mammals, and gradually humans, took a huge advantage of this.