NEW BRUNSWICK/PISCATAWAY, N.J. – New abilities to detect layers of "space dust" in the earth's crust are building geological evidence that comets or asteroids colliding with earth not only helped wipe out the dinosaurs, but may have originally helped bring them to prominence about 200 million years ago. Dennis V. Kent, Rutgers geology professor, was among a team of geologists who analyzed footprints, bones and plant spores in more than 70 locations in eastern North America, as well as iridium dust and magnetic fields in four corresponding sediment layers in the Newark Basin. The team published its findings, "Ascent of Dinosaurs Linked to an Iridium Anomaly at the Triassic-Jurassic Boundary," in the May 17 edition of the journal Science.
"Finding the element iridium, which is common in space objects, creates a time marker for comet or asteroid impacts." said Kent. "Correlating the finds with evidence of plant and animal life helps to tell us what happened."
Using high-resolution mass spectrometry technology provided by Christian Koeberl of the University of Vienna in Austria, the scientists were able to make unprecedented comparisons of iridium levels in the parts-per-trillion range. Earlier attempts to find an iridium "spike" at the boundary between the Triassic and Jurassic periods had been hampered because the spectrometry equipment, which identifies materials by comparing their mass, was not sensitive enough.
Kent said another important find was a thin zone in the sediment, just below the Triassic-Jurassic boundary, where the magnetic field is reversed. This reverse zone can now serve as a marker to help identify the boundary location in the geological record.
"Our research adds to the speculation that there was a comet or asteroid impact about 200 million years ago, followed relatively quickly by the rising dominance of dinosaur populations of the Jurassic period," said Kent. He suggested that the effects of the impact killed off or reduced many competitive species, clearing the way for dinosaurs to adapt and flourish.
"Dinosaurs went on to dominate for the next 135 million years," he said, noting that their extinction is now commonly attributed to the ecological effects of yet another comet or asteroid impact – this one about 65 million years ago.
Besides his work at Rutgers, Kent is associated with the Lamont-Doherty Earth Observatory of Columbia University, as are his co-authors E.C. Rainforth and P.E. Olsen. Olsen's earlier research about Triassic-Jurassic transitions inspired the project. Other co-authors include Koeberl and H. Huber of the University of Vienna, H.-D. Sues of the Royal Ontario Museum, A. Montanari of the Osservatorio Geologio do Coldigiocom in Italy, S.J. Fowell of the University of Alaska-Fairbanks, and M.J. Szajna and B.W. Hartline, fossil collectors of Reading, Pa.
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