Geologists Discover New Way of Estimating Size and Frequency of Meteorite Impacts

Scientists have developed a new way of determining the size and frequency of meteorites that have collided with Earth.Their work shows that the size of the meteorite that likely plummeted to Earth at the time of the Cretaceous-Tertiary (K-T) boundary 65 million years ago was four to six kilometers in diameter. The meteorite was the trigger, scientists believe, for the mass extinction of dinosaurs and other life forms.

When meteorites collide with Earth, they carry a different osmium isotope ratio than the levels normally seen throughout the oceans. The vaporization of meteorites carries a pulse of this rare element into the area where they landed.The osmium mixes throughout the ocean quickly. Records of these impact-induced changes in ocean chemistry are then preserved in deep-sea sediments.The record in marine sediments allows to discover how osmium changes in the ocean during and after an impact

The scientists expect that this new approach to estimating impact size will become an important complement to a more well-known method based on iridium. Even though these method works well for the K-T impact, it would break down for an event larger than that: the meteorite contribution of osmium to the oceans would overwhelm existing levels of the element, researchers believe, making it impossible to sort out the osmium's origin.

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 size of the K-T meteorite as four to six kilometers in diameter.
Scientists feel that this will help them in analysing the causes of yesteryears that have remained unexplained till now.