The Question of Dionosaur Extinction
Chances are, most every life form on Earth will someday be extinct. Paleontologists study fossilized evidence of ancient life. They say that 99.9 percent of all life forms that ever inhabited our planet are now extinct. Of course, this percentage is only an estimate since no one knows exactly how many life forms have lived here.

As many as 50 million species might live on Earth today and possibly more than 50 billion species have lived on Earth during its 4.6 billion-year history. Scientists agree on one thing: Extinction, the total eradication of a related group of organisms, is apparently a very common occurrence. It has happened before, is happening now, and will continue to happen.

Paleontologists have provided us with much information about the particularly interesting extinction of the dinosaurs. Thousands of dinosaur species became extinct over millions of years, but others always took their ecological places. Then, 65 million years ago the last species of dinosaurs became extinct. How long it took we do not know. Their extinction is a dual mystery. Why did some individual species survive extinctions that occurred during the Triassic, Jurassic, periods? And why did none of them survive the Cretaceous extinction of 65 million years ago?

We have given the students information on a number of possible extinction causes. It is up to them to argue for a single cause or a combination.

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