Washington: The meteorite linked to the mass extinction of dinosaurs and other life forms 65 million years ago was four to six kilometres in diameter.

That's the conclusion of a team of Hawaii University researchers who have evolved a mechanism to measure the size of meteorites that have rammed into earth over millennia. François Paquay and his team used isotopes of the rare element osmium in sediments at the bottom of the ocean to estimate the meteorite sizes and also the frequency with which they hit earth.

Paquay's team included Tarun Dalai from the Indian Institute of Technology (IIT) at Kharagpur. Paquay analysed samples from two meteorite-hit sites and measured osmium isotope levels during the late Eocene period, a time during which large meteorite impacts are known to have occurred.

"The record in marine sediments allowed us to discover how osmium changes in the ocean during and after an impact," said Paquay. "The vaporization of meteorites carries a pulse of this rare element into the area where they landed," said Rodey Batiza of the National Science Foundation (NSF), which funded the research.

"The osmium mixes throughout the ocean quickly. Records of these impact-induced changes in ocean chemistry are then preserved in deep-sea sediments," he added. Under the assumption that all the osmium carried by meteorites is dissolved in seawater, the geologists were able to use their method to estimate the K-T meteorite that wiped out the dinosaurs was four to six kilometres in diameter.

The scientists expect that this new approach to estimating impact size will become an important complement to a better-known method based on iridium. Paquay, Dalai and other researchers have published their findings in the latest issue of the journal Science.

Source : IANS