Earth, Stars Meet at Rochester

Most scientists have long agreed that the reign of dinosaurs came to an end when an asteroid or comet slammed into Earth about 65 million years ago.

Now, new research by a Rochester team led by Robert Poreda, associate professor of earth and environmental sciences, is shedding light on a similar event that may have helped pave the way for the great lizards' dominance.

By making sensitive measurements of helium and argon isotopes that could only have arrived on Earth from outer space, Poreda-joined by scientists from the University of Washington, NASA, and New York University-pinpointed a cataclysmic impact about 251 million years ago.

Setting off a chain of volcanic eruptions that covered the planet in sediment, ash, and carbon dioxide, the blast could account for why more than 90 percent of marine animals and about 70 percent of land vertebrates disappeared during the boundary between the Permian and Triassic (P/T) eras, an extinction so pronounced it is known to scientists as "The Great Dying," the team argues.

The same combination of events has been documented during the Cretaceous/Tertiary (K/T) boundary, the time when dinosaurs disappeared.

"These two extinctions are like bookends for the age of the dinosaurs," Poreda says. "The P/T boundary helped to usher in the age of the dinosaurs, and the K/T boundary snuffed it out."

The study, published in Science, was one of several new glimpses of the Earth and the universe provided by Rochester scientists in the last year.

In a separate study, Arial Anbar, assistant professor of earth and environmental sciences and of chemistry, provided evidence that even during the extraordinarily violent era in Earth's early history, the young planet was hospitable enough for microbes to survive.

Studying a time 4 billion years ago, when Earth was hit by asteroids so frequently that scientists call the period the "Late Heavy Bombardment," Anbar and his team determined that only rarely-perhaps once every 30 to 100 million years-was the bombardment so severe that microbes would have had difficulty surviving.

And in another view of the universe, a team of Rochester astrophysicists may have discovered the mechanism behind planetary nebulae, the wispy clouds of light that radiate from some dying stars.

In a paper published in the January 25 issue of Nature, University astrophysicists John Thomas, Andrew Markiel, Hugh Van Horn, Adam Frank, and Eric Blackman suggest that a magnetic dynamo-similar to the kind that produces storms on the sun-appears to shape planetary nebulae.

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