- History of life on the Earth witnessed five mass extinctions
of species as a result of natural calamities. Currently, biologists are
talking more and more often about the sixth wave of extinction provoked
in many respects by human beings. This opinion is shared by a Russian sea
fauna diversity specialist A.V. Adrianov (Institute of Maritime Biology,
Far-East Branch, Russian Academy of Sciences). Research in this area has
been supported by the Far-East Branch of the Russian Academy of Sciences,
CRDF, Ministry of Education and Science of the Russian Federation, and
the Foundation for Promotion of Russian Science and the Russian Foundation
for Basic Research.
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- As of today, taxonomists have already described nearly
2 million species, although in fact their number varies, according to various
estimates, from 5 to 100 million. But 90 to 99 percent of species ever
existing on the planet have already become extinct. The overwhelming majority
vanished as a result of the so-called normal or background extinction due
to the limited period of biological species existence, which fluctuates
from 1 million years with mammals through 11 million years with some marine
invertebrates. Besides the background extinction, the fauna experienced
five mass extinctions, as a result of which 50 to 95 percent of then existing
species disappeared within a limited historical period. The first mass
extinction occurred 440 million years ago, at the end of Ordovic, as a
result of temperature fall and the ocean level lowering. The second wave
took place during the late Devonian, again due to temperature fall and
sea reliction. During the third wave of extinction, at the end of Permian,
approximately 250 million years ago, 95 percent of marine species and nearly
70 percent of terrestrial ones disappeared. The catastrophe was probably
caused by active reconstruction of the earth's crust and change of climate
during formation of the supercontinent Pangaea. The forth extinction happened
in the late Trias, and the fifth one the most renowned extiction
hit 65 million years ago. Researchers are inclined to believe that
the Earth came into collision with a large bolide at that time. As a result,
sea shoals suffered from tsunami and acid rains, the seabed was covered
by enormous amount of organic matter, and only 12 percent of the then existing
species survived on land.
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- At present, according to numerous specialists' opinion,
the sixth - pleistocene - wave of extinction is coming, which has been
in many respects provoked by men. Given the current average extinction
rate of 40 species a day, it would take only 16 thousand years for the
extinction of 96 percent of the contemporary biota exactly as much
as died out during the period of disastrous Permian extinction. The major
reason for the oncoming calamity is destruction of plants' and animal's
ecotope. Scientists have estimated that the species life span for contemporary
mammals and birds has decreased up to 10 thousand years, i.e. it became
100 to 1000 times shorter than that of fossil forms. If the habitat continues
to be destroyed at the same pace, the life span of these species will soon
make only 200-400 years. There are no such estimates for the invertebrates,
but they are undoubtedly affected both by the global environment and climate
change, and by disappearance of local biotopes.
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- Death reigns on land and at sea. Thus, about 1 percent
of tropical rainforests disappears annually. Up to 70 plant and animal
species become extinct every day, which makes about 3 species per hour.
At present, one tenth of coral reefs zones of the highest biological
diversity at shallow water perishes; about 30 more percent will be
ruined in the next decades. Corals die out mainly due to global environment
and climate change, reef fish catching, water contamination and warming,
hurricanes, destruction of symbiotic organisms. Any events taking place
in shallow water also affects sea depths. Perhaps only "autonomous"
superorganisms of deep-water gas-hydrotherm have not been touched upon
by anthropogenic impact and they will evidently be able to escape consequences
of the planet's global environment and climate changes even in case of
nuclear holocaust.
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- Nevertheless, the sixth mass extinction is oncoming.
That will be the first extinction which did not happed due to natural reasons
but as a result of activity of one biological species, whose quantity increases
annually by 100 million individuals.
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- http://www.innovations-report.com/html/reports/life_sciences/report-31436.html
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