More than 90 percent of all
organisms that have ever lived on Earth are extinct. As new species evolve to
fit ever changing ecological niches, older species fade away. But the rate of
extinction is far from constant. At least a handful of times in the last 500
million years, 50 to more than 90 percent of all species on Earth have
disappeared in a geological blink of the eye.
A mass extinction or extinction
event is the phenomenon in which a large number of species of life on Earth
become extinct in a relatively short period of time. In general usage by
scientists, "mass extinction" refers to an extinction affecting a
great many different groups of organisms occupying diverse and wide-spread
environments. Extinction of species, genera, families, and even orders of
organisms has occurred throughout the history of life on Earth, but mass
extinctions are those events that greatly exceed the normal or background
about 65 million years ago, probably caused or aggravated by impact of
several-mile-wide asteroid that created the Chicxulub crater now hidden on the
Yucatan Peninsula and beneath the Gulf of Mexico. Some argue for other causes,
including gradual climate change or flood-like volcanic eruptions of basalt lava
from Indias Deccan Traps. The extinction killed 16 percent of marine families,
47 percent of marine genera (the classification above species) and 18 percent of
land vertebrate families, including the dinosaurs.
End Triassic extinction,
roughly 199 million to 214 million years ago, most likely caused by massive
floods of lava erupting from the central Atlantic magmatic province -- an event
that triggered the opening of the Atlantic Ocean. The volcanism may have led to
deadly global warming. Rocks from the eruptions now are found in the eastern
United States, eastern Brazil, North Africa and Spain. The death toll: 22
percent of marine families, 52 percent of marine genera. Vertebrate deaths are
about 251 million years ago. Many scientists suspect a comet or asteroid impact,
although direct evidence has not been found. Others believe the cause was flood
volcanism from the Siberian Traps and related loss of oxygen in the seas. Still
others believe the impact triggered the volcanism and also may have done so
during the Cretaceous-Tertiary extinction. The Permian-Triassic catastrophe was
Earths worst mass extinction, killing 95 percent of all species, 53 percent of
marine families, 84 percent of marine genera and an estimated 70 percent of land
species such as plants, insects and vertebrate animals.
Late Devonian extinction,
about 364 million years ago, cause unknown. It killed 22 percent of marine
families and 57 percent of marine genera. Erwin said little is known about land
organisms at the time.
about 439 million years ago, caused by a drop in sea levels as glaciers formed,
then by rising sea levels as glaciers melted. The toll: 25 percent of marine
families and 60 percent of marine genera.
The IUCN Red List of Threatened
Species (version 2010.4) contains 55,926 species and 33% of these (18,351
species) are known to be threatened. This is a minimum estimate; at least some
of the 8,358 Data Deficient species will be threatened (many will be rare or
restricted range species).
Estimates of global species
diversity have varied from 2 million to 100 million species, with a best
estimate of somewhere near 10 million, and only 1.75 million known species of
living organisms on earth have been identified.
biological impoverishment of the Earth is accelerating as human
population grows. The share of bird, mammal, and fish species that are
now in danger of extinction is in double digitsó11 percent of all bird
species, 25 percent of mammals, and 34 percent of fish. Over
19,000 plant species and 5000 animal species are classified as endangered.
threatened species are at risk from human activities.
are home to 50 to 70% of all life forms on Earth. Coral
and the Oceans are home to 25% to 30% of all life forms. At the current rate
of destruction how long will it be before human beings become endangered?
estimate an average of 137
species of life forms are driven into extinction every day
for a total of 50,000
The greatest mass
extinction of species since the extinction of the dinosaurs 65 million years ago
is now occurring. If present trends continue one half of all species of life on
earth will be extinct in less than 100 years, as a result of habitat
destruction, pollution, invasive species, and climate change.
Seven out of ten biologists
believe that we are in the midst of a mass extinction of living things, and
that this dramatic loss of species poses a major threat to human existence
in the next century.
In strong contrast to the
fears expressed by scientists, the general public is relatively unaware of
the loss of species and the threats that it poses.
This mass extinction is the
fastest in Earth's 4.5-billion-year history and, unlike prior extinctions,
is mainly the result of human activity and not of natural phenomena.
Scientists rate biodiversity
loss as a more serious environmental problem than the depletion of the ozone
layer, global warming, or pollution and contamination.
believe that we must act now to address the biodiversity crisis. The
majority of scientists believe the crisis could be averted by a stronger
stance by policymakers and governments and by individuals making changes in
their daily lives.
Scientists believe some of the
most important effects of this dramatic species loss are:
Serious impairment of the
environment's ability to recover from natural and human-induced
Destruction of the natural
systems that purify the world's air and water.
Reduction of the potential
for the discovery of new medicines.
drought, and other environmental disasters.
to the degradation of the world's economies, thereby weakening the
social and political stability of nations across the globe.
compiled from The British Antarctic Study, NASA, Environment Canada,
UNEP, EPA and other sources as stated and credited Researched by Charles
Welch-Updated daily This Website is a project of the The Ozone Hole Inc.
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