SEM of Meteorite from the Cretaceous-Tertiary (KT) extinction event, also known as the KT boundary, was a period of massive extinction of species that occurred about 65.5 million years ago. The spheres shown here represent material that was melted from a large meteorite impact. Flung high into the earth's atmosphere, these hot particles rained down, killing most life on the planet. These specimens are from Spain and were photographed at 145x magnification.