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Biosphere Community

The Six Great Extinctions

 

 

The biosphere has been severely attacked six times, periods when great numbers of multi-cellular species (eucaryotes) were killed off and became extinct. Five of these extinction periods happened long ago, and they are inferred from the fossil record. For example, a species community is abundant in fossil sediments, but suddenly disappears. When this happens in the same fossil strata to many, many species in many locations around the planet, paleontologists know that a catastrophe must have ocurred. Normal species extinctions happen slowly. In some extinctions, after a great deal of detective work, the cause is known. For instance, 251 million years ago (mya), at the end of the Permian Period, a vast series of volcanic eruptions darkened the sky for many years. Earth became very cold, a dark Winter Planet. Paleontologists estimate that 96% of all marine species and 70% of land species disappeared forever.

Extinction seems to be the fate of most organisms that have ever lived. Species become extinct when they are no longer able to survive in changing conditions. A typical species becomes extinct within 10 million years of its first appearance, although some species, called living fossils, survive virtually unchanged for hundreds of millions of years. Only one in a thousand species that have existed remain alive today.

Mass extinctions are rare events, and they take place more slowly than a catastrophe film is going to show. They may look abrupt in fossil rock strata, but actually may have taken hundreds of thousands, or even millions of years.

 

The Five Great Extinctions

 

A few of the species wiped out in the first 5 extinctions

The Sixth Great Extinction--
the Holocene Extinction--
is happening right now


The Sixth Extinction has been going on since humanity began to increase. Extinction has accellerated tremendously since Industrialization, especially in the last fifty years. A recent study that shows 50% of all plant and animal species going extinct is summarized here by Science Daily (Oct 21, 2008)

10,000 BC to Present Human impact is enormous. Thousands of species have vanished because of human impact. In 10,000 years, our numbers have swollen from about 6 million to 6 billion (6,000,000,000). Each year about 50,000 species go extinct (fifty thousand!) because of habitat loss, over-harvesting of the ocean, agricultural poisoning, roads, suburbia and monoculture forestry. The rate of mass extinction is rising daily. Biodiversity is being lost, and we have no solutions in sight.
Passenger Pigeon, once the most numerous bird on Earth
Cave Bear
Dodo
Giant Sloth

Wooly Mammoth, Wooly Rhino
Carolina Parakeet
A tiny fraction of species gone extinct since the advent of humanity

Five of the great extinctions took place long ago--MYA means "millions of years ago."

end of
Ordovician

440
mya
Enormous glaciation and lowering of sea levels. 60% of species disappeared
end of
Devonian
365 mya Glaciation and falling sea levels again. Maybe meteorite too. 70% of species wiped out.
end of
Permian
225 mya Huge volcanic eruptions. Earth became winter. . 90% to 95% of all species extinct.
end of
Triassic
210 mya Maybe a comet shower. Most ocean reptiles extinct. Many amphibians extinct.

end of Cretaceous

called the KT
extinction

65 mya Meteorite struck Earth. Dinosaurs, marine reptiles, ammonoids and many species of plants were wiped out. Mammals, early birds, turtles, crocodiles and amphibians less affected.

 

 

The Extinction of Experience

When a species disappears from a particular locale, the experience of that species by local people is effectively extinct. To describe this kind of loss, Naturalist Robert Michael Pyle coined the phrase "the extinction of experience."

Children growing up without any experience of such missing species can not care about their loss. They don't even know they're gone. Beings which could have enriched their lives have not. Older people can feel sorrow about that; the children can't, which makes it difficult for them to support efforts to preserve biodiversity.

Intimate personal experience is what creates our powerful bonds with Nature. We do not love Nature in the abstract, but in the particulars: that green moss gleam revealed by melting snow; the flashed rainbow of dragonfly wings; eye contact with a deer.

 

 

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