"Human beings are currently causing the greatest mass extinction of species since the extinction of the dinosaurs 65 million years ago. If present trends continue one half of all species on earth will be extinct in 100 years.

A majority of the nation's biologists are convinced that a "mass extinction" of plants and animals is underway that poses a major threat to humans in the next century.

"The speed at which species are being lost is much faster than any we've seen in the past -- including those [extinctions] related to meteor collisions," said Daniel Simberloff, a University of Tennessee ecologist and prominent expert in biological diversity who participated in the museum's survey. [Note: the last mass extinction caused by a meteor collision was that of the dinosaurs, 65 million years ago.]"