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Research reported in the journal Science today suggests that the rise of large tetrapod dinosaurs 208 million years ago may have occurred due to the impact of an asteroid or comet with the Earth. The team, lead by P. Olsen from Lamont-Doherty Earth Observatory of Columbia University, USA have discovered a layer at the boundary between the Triassic and Jurassic Periods containing iridium. Such Ir anomalies are associated with the collision of asteroids and comets with the Earth since this element is found in low abundance in terrestrial rocks but is abundant in meteorites and NEOs. An increase in the amount of pollen and spores from ferns was found associated with the Ir anomaly and this coincidence mirrors the pattern observed at the K-T boundary, at which the dinosaurs became extinct, where ferns were the first plants to recover from the impact. Olsen and colleages suggest that the Ir anomaly and the fern spike suggest that the appearance of large dinosaurs over only 30.000 years was the result of a mass extinction caused by a large impact. Other scientists, however, suggest the new research is not conclusive. 'Whereas the amount of iridium in the K-T boundary layer is roughly equal to that expected to be present in a 6 mile wide comet, that measured at the Triassic-Jurassic layer is many times less and it may be too small to represent a large impact' said Dr Matthew Genge of the Natural History Museum. Genge suggests that despite the similarity between the patterns at the K-T and Triassic-Jurassic boundaries the amount of Ir in the layer might be explained by its concentration chemically or biochemically on the Earth's surface.
More info: Science
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