Geologists have discovered a new way of estimating the size of impacts from meteorites. Click on image for full size (100 Kb) Courtesy of NASA

Scientists have developed a new way of determining the size and frequency of meteorites that have collided with Earth. Meteorites contain a rare element called osmium, and they have different levels of this element than the levels normally seen in the oceans on Earth. When a meteorite hits the Earth, the osmium is released where the meteorite landed. If it lands in the ocean, the osmium mixes in the ocean very quickly. Eventually these new levels of osmium settle into deep-sea sediments. Scientists can collect samples of the sediments many years later and learn about the meteorites that hit the Earth in the past.

By studying deep-sea sediments, scientists have learned 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 across. The meteorite was the trigger, scientists believe, for the mass extinction of dinosaurs and other life forms.

One of the scientists involved in this study, François Paquay, said that this new technique will allow scientists to learn more about many other meteorites that have hit the Earth.