7/24/2009
Mass Extinctions
The history of life on Earth has been
disrupted by major catastrophic
events, such as major volcanic
eruptions or the impacts of asteroids.
There have been at least five mass
extinctions in which many types of
plants and animals were wiped out.
• However, after each extinction, new life
forms emerge.
• Scientists estimate that 1/20 of 1% of all
the species that have ever existed on Earth
are living today.
• All the other species existed in the past and
then became extinct.
It is known as the Permian extinction,
and it killed as many as 90 percent of all
living things on Earth.
Mass extinctions are periods of
large-scale
large
scale extinction
extinction.
The Permian Extinction – The Greatest
Mass Extinction
• Scientists believe the
greatest mass extinction
was about 250 million
years ago towards the
end of the Paleozoic era
• See a 13 minute video
clip from PBS to learn
more.
http://www.pbs.org/wgbh/nova/sciencenow/video/3318/q01-220.html
Although its cause is still open to debate,
scientists have evidence that the largest
volcanic eruption in Earth history, known as the
Siberian Traps, occurred at the same time as the
Permian Extinction.
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The Siberian Traps
sent particles of dust
into the atmosphere
and changed Earth’s
climate causing longand short-term
changes in the
habitats of
organisms living at
that time.
The most recent mass extinction, the
Cretaceous-Tertiary extinction,
happened about 65 million years ago
ending the Mesozoic era.
Scientists believe the Cretaceous-Tertiary
extinction was caused by an asteroid impact.
An enormous asteroid hit Earth with an
impact so violent that huge amounts of
dust were thrown into the atmosphere
blocking the sun possibly for years.
Afterwards, mammals became the
dominant vertebrate life form on land.
These changes in climate and habitats
caused the extinction of the dinosaurs.
A sixth mass extinction?
• Today, some scientists think we are in the
middle of a sixth mass extinction because
many species have become extinct in the
last few hundred years.
• This time, human impact may be the cause.
• But humans can also help prevent
extinctions.
• The California condor is one example.
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A typical California condor has a 10foot wingspan, making them the largest
bird in North America.
Government and private groups have
created the California Condor Recovery
Program.
• Because of the
program, there are
now almost 300
condors, over 100
of them in the wild
in California, Baja
California, and
Arizona.
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