What caused the extinction of the dinosaurs?
In 1980, American geologist Walter Alvarez and his colleagues at the University of Berkeley came up with this astounding theory: an asteroid 10 miles wide slammed into Mexico’s Yucatan Peninsula and dug a crater 60 miles wide and 15 miles deep, causing a horrendous cataclysm that doomed half of the world’s plant and animal life, including the dinosaurs that had ruled the planet for 160 million years. They came up with the theory after finding iridium—a rare metallic element known to be present in asteroids—in layers of clay in various parts of the world, and they also found in Mexico what they concluded was the crater caused by the asteroid impact.
Their theory caused uproar in the scientific community, particularly from other experts who maintained that based on evidence, that asteroid impact couldn’t have caused the mass extinction because it must have occurred at least 300,000 years before the start of the mass extinction. These experts theorized instead that the mass extinctions were caused by massive volcanic eruptions, which they calculated to have emitted 30 times more life-killing sulfur fumes than any asteroid impact could. Today, however, an international team of scientists has concluded that Alvarez and his colleagues were right.
In the March 5, 2010 issue of the
San Francisco Chronicle, Science Editor David Perlman reports that 41 noted scientists from a wide array of disciplines—geophysics, paleontology, climatology, geochemistry, microbiology, zoology, botany, and several others—have concluded that as Alvarez and his team had theorized, the evidence is conclusive that a single asteroid impact was the ultimate cause for the mass extinctions. The scientists’ report was published in the most recent issue of the journal Science.
Read David Perlman’s “Settled: Dinosaurs done in by asteroid” in the San Francisco Chronicle now!RELATED READING:Paul Murdin, a leading authority on astronomy and astrophysics, has come up with a highly readable, interesting, and lavishly illustrated history and introduction to astronomy for the general reader. The book,
Secrets of the Universe: How We Discovered the Cosmos, discusses in 70 episodes what humankind has learned about the universe over the centuries and provides an overview of what possible new enigmas scientists might unravel about it the near future. It traces humankind’s slow but cumulative realization that Earth is not actually the center of the universe as they thought but only a tiny planet among millions of other planetary systems in the universe.
Read A.C. Grayling’s essay about The Secrets of the Cosmos in The Thinking Read now!
