Asteroid impact. Illustration of a large asteroid colliding with Earth on the Yucatan Peninsula in Mexico. This impact is believed to have led to the death of the dinosaurs some 65 million years ago. The impact formed the Chicxulub crater, which is a...

Artwork showing the Earth now (right) compared to how it might have looked around 2.4 billion years ago, before the great oxygenation event. The continents back there bear no resemblance to their modern counterparts; the atmosphere would have been th...