Science/Medicine : Volcanism, Not Meteors, Cited in Dinosaur Demise

The mass extinctions of dinosaurs and other organisms 65 million years ago were the consequence of disturbances triggered deep within Earth, rather than asteroids crashing into Earth, says British geologist Anthony Hallam of the University of Birmingham.

In article in the current Science magazine, Hallam disputes the popular hypothesis that the extinction of dinosaurs, plants and other life was the result of catastrophic fires, dust clouds and climatic changes touched off by asteroids striking Earth.

He called the impact hypothesis a “brilliant success” for stimulating “an immense amount of fruitful research” since it was proposed in 1980 by Nobel laureate Luis W. Alvarez, his son, Walter Alvarez, and other geologists at the University of California, Berkeley.

However, Hallam wrote, “there exist legitimate grounds for doubt. . . . “

He said isotopes or chemically distinctive signatures in the rocks, inconsistencies or other explanations for geologic features, and the absence of a big enough crater on Earth all undermine the impact hypothesis.

Furthermore, Hallam argued, the extinctions of some species were too gradual or too selective to have been caused by such a catastrophic event.

He acknowledges a massive sudden extinction of species of plankton, or microscopic ocean animals and algae, but he argues that this may have been caused by a sudden change in ocean chemistry.

Hallam proposes that thermal forces drove “mantle plumes” of heat and molten rock toward the surface of Earth, causing volcanoes on a scale that has never been recorded in historic time.