| Scientists have concrete evidence that the Earth is | | | | - The Triassic-Jurassic Extinction occurred 200 million |
| currently undergoing the largest mass extinction in 65 | | | | years ago. Was it caused by climate change, |
| million years. Over 50 species are going extinct every | | | | asteroids, or volcanoes? The verdict isn't clear. What |
| single day. | | | | is clear is that 20% of marine life and many large |
| It's called the Holocene Extinction -- Holocene being | | | | amphibians were wiped out. At least half of all |
| the current epoch that began at the end of the last | | | | species on the planet bit the dust. This event |
| ice age, about 10,000 years ago. | | | | occurred over less than a 10,000 year period, just |
| From Earth's fossil record, we know about Six Great | | | | before the supercontinent of Pangea began to break |
| Mass Extinctions: | | | | up. |
| - The Ordovician-Silurian Extinction occurred about | | | | - The Cretaceous-Tertiary Extinction occurred about |
| 444 million years ago. At the time, all complex | | | | 65 million years ago. This event was probably caused, |
| organisms lived in the sea. The most common theory | | | | or at the least aggravated by, the impact of an |
| is that the onset of an ice age caused the extinction, | | | | asteroid around the size of Manhattan. About 16% of |
| which wiped out over 100 families of marine life. | | | | marine families and 18% of land vertebrate families |
| Many trilobite families bit the dust during this event. | | | | ceased to exist. In North America, over 50% of plant |
| - The Late Devonian Extinction happened 364 million | | | | species may have been wiped out. And of |
| years ago. This event saw a major worldwide | | | | course...this is the event that doomed the dinosaurs. |
| extinction of coral reefs and the marine life they | | | | - The Holocene Extinction is occurring now. Studies of |
| supported, as well as other groups of animals and | | | | the fossil record show that the normal "background" |
| plants. Nobody's sure what caused it, but scientists | | | | rate of extinction is about one species every four |
| speculate global cooling and several medium-sized | | | | years. The current rate is between 30,000 and |
| asteroid impacts within a few million years of each | | | | 100,000 per year. You are now witnessing the |
| other may have been the culprits. | | | | fastest of the six great mass extinctions. And this |
| - The Permo-Triassic Extinction occurred 251 million | | | | extinction, without a doubt, is the result of human |
| years ago. The granddaddy of all mass extinctions, | | | | population growth. By the end of this century, over |
| this event saw 96% of all marine species and 70% | | | | five million species (half of the species on Earth now) |
| of land vertebrate species kick the evolutionary | | | | will likely be gone. "It's not just species on islands or |
| bucket. The die off happened in less than a million | | | | in rain forests or just birds or big charismatic |
| years (a very short time in geological terms) and the | | | | mammals," says Stuart Pimm, a conservation biologist |
| recovery took 5 million years to crank back up, and | | | | researcher from the University of Tennessee. He |
| another million years after that to get rolling. While | | | | notes fish, birds, insects, plants, and mammals. "It's |
| not deemed the smoking gun yet, this event | | | | everything and it's everywhere...it is a worldwide |
| coincides with the largest known volcanic eruption in | | | | epidemic of extinctions. |
| history. | | | | |