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Mass
extinction has taken place on earth quite a few times. Mass
extinction refers to extinction on a global scale. This has happened
when due to some change in the atmospheric make up there has been
extensive loss of plant and animal life in all the ecosystems on
earth.
In
the past 500 million years, five such mass extinctions have taken
place. The first occurred 438 million years ago and a very major
part of the earth’s plant and animal life was wiped off the face
of earth. Following the process of evolution, many different
varieties of plant and animal life flourished once again on earth.
Then 368 million years ago another mass extinction took place and
again a little over eighty per cent of plant and animal life was
lost.
Nature
has to take her course and the next mass extinction occurred again
245 million years ago. In this extinction, ninety six per cent of
all the species present on earth was the loss suffered. After this
many new groups of animals evolved.
The
next mass extinction happened 208 million years ago. Of the last
mass extinction that occurred it is believed that the cause was a
meteorite colliding with the earth. It is believed that this brought
about many atmospheric changes. One major fall out is believed to be
a thick layer of dust and gases over the earth, which cut off
sunlight totally. As a result plants could no longer make food and
withered away. Other life forms, which depended on plants also lost
their source of food and died. Once the food chain was broken there
was rapid destruction of life forms all over the earth. Other
theories for this mass extinction are that it was a result of
volcanic activity.
All
such natural events, including that of extinction (mass extinction
included) seem to have a purpose. Other than mass extinction, a type
of extinction occurs as a gradual process. Superior versions of a
species edge out the earlier and inferior versions. Each successive
cycle of species that evolved proved to be better than its
predecessor.
Naturalists
have observed that once in every million years an average of three
species becomes extinct. Man’s evolution from a primate is a prime
example of this.
The reason given for this happening is that survivors of
every such extinction have had to live in unfamiliar surroundings
and adapt themselves to it. This has led to the evolving of better
features in every species that has survived. Most species are so far
removed from what the original species might have been millions of
years ago that they bear absolutely no resemblance to them.
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