Climate change on a prehistoric Earth. Illustration showing the effects of an asteroid strike on a prehistoric Earth, causing global cooling followed by a greenhouse effect. The sequence starts at top left, with an extended polar ice cap and a supercontinent around the equator. Following a major asteroid impact (top right), debris is ejected into the atmosphere. At centre left, the impact has triggered the eruption of a supervolcano and the subsequent effects on the atmosphere reduces the amount of sunlight reaching the surface. At centre right, the polar icecaps grow and heat is reflected back into space, cooling the Earth further. Eventually, the entire planet is frozen (a Snowball Earth, bottom left), with volcanoes erupting through the ice. As greenhouse gases accumulate in the atmosphere, heat from the Sun is trapped and the Earth thaws (bottom right).