What Wiped Out The Dinosaurs?

By LEON JAROFF

Nearly all of us now know--or think we know--how the dinosaurs perished: some 65 million years ago, a giant asteroid or comet struck the earth, spewing huge amounts of dust and debris into the air. That dust, according to a widely accepted theory first proposed by Nobel laureate Luis Alvarez, was circulated by the winds and enshrouded the earth for months, blocking sunlight and causing temperatures to plummet. As a result, the dinosaurs, and 70% of all other terrestrial species, were wiped out.

But this scenario was rudely challenged last week by Kevin Pope, a former NASA scientist. Reviewing recent studies of atom-bomb blasts and analyses of particles in strata at the 65 million-year level, he concluded in Geology that most of the dust particles were too large to have remained suspended in the air for many months. The finer particles that stayed airborne would not have blocked enough sunlight to cause mass extinctions. Pope speculates instead that soot from the worldwide conflagrations, sulfate aerosols and other impact phenomena were to blame. His findings prompted such headlines as ALVAREZ TEAM WAS WRONG and DUST DIDN'T DO IT, and heartened the relatively few scientists who still contest the Alvarez theory. Others, however, dispute Pope's analysis and say his methodology was faulty. While acknowledging other contributory factors, they still believe dust was the major component of the sun-blocking shroud that dispatched the dinosaurs.

--By Leon Jaroff