By Sid Perkins
Evidence from 65-million-year-old sediments suggests that a single impact from space wiped out the dinosaurs and that ecosystems recovered from the trauma in only a few thousand years.
Researchers analyzed layers of ocean sediments deposited during a 1.5-million-year period in Italy and Tunisia. Among these was the thin clay layer that marks when the dinosaurs became extinct. The scientists found that the concentrations of the isotope helium-3 in the sediments didn’t vary during those 1.5 million years. This indicates that the extinction-triggering object that struck Earth 65 million years ago wasn’t part of a long-term comet shower, the researchers say.
Such a shower would have produced far more comet dust and delivered far more helium-3, which is 300 times more common in space than on Earth, says Sujoy Mukhopadhyay, a geochemist at the California Institute of Technology in Pasadena.
Mukhopadhyay and his colleagues calculated the rate at which helium-3 was deposited in the sediments. Then they used this rate as a cosmic clock to determine that the clay layer marking the dinosaur extinctions was deposited in only 10,000 years.
The lack of fossils in the clay layer indicates an abrupt onset for the extinction. The appearance of fossils just above the impact layer marks a sudden proliferation of new species in ocean ecosystems, Mukhopadhyay says. He and his colleagues report their analysis in the March 9 Science.
