HOW DO WE KNOW?

FIG. 1.3

What caused the extinction of the dinosaurs?

BACKGROUND Dinosaurs were diverse and ecologically important for nearly 150 million years but became extinct about 66 million years ago.

OBSERVATION

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FIG. 1.3
Photo Source: Kirk Johnson, Denver Museum of Nature & Science.

HYPOTHESIS The impact of a large meteorite disrupted communities on land and in the sea, causing the extinction of the dinosaurs and many other species.

PREDICTIONS Independent evidence of a meteor impact should be found in rock layers corresponding to the time of the extinction and be rare or absent in older and younger beds.

FURTHER OBSERVATIONS

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Photo Source: Dr. David Kring/Science Source

CONCLUSION A giant meteor struck Earth 66 million years ago, causing the extinction of the dinosaurs and many other species.

FOLLOW-UP WORK Researchers have documented other mass extinctions, but the event that eliminated the dinosaurs appears to be the only one associated with a meteorite impact.

SOURCE Alvarez, W. 1998. T. rex and the Crater of Doom. New York: Vintage Press.