A meteorite of about 10km across may have caused the mass extinction at the end of the Cretaceous period, about 65 million years ago. Sixty percent of all the species on Earth at the time became extinct, including the dinosaurs.
There is a crater of about this age on Yucatan Peninsula of Mexico, which is 180 kilometres wide. The crater is now buried, but its outline is visible on geophysical surveys.
It would take 100 million megatons of TNT to create a crater of this size! Vast amounts of dust would be thrown into the atmosphere, blocking out the sun. This would affect the growth of plants and the animals which depend on them.
Geologists are still not sure whether or not the mass extinction was caused by this impact. However, we are sure that a vast meteorite hit the Earth at this time.