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EARTH'S VISITORS FROM SPACE Although Earth has not yet been visited by aliens (although some people believe otherwise), it does still get other visitors from space. These visitors come in the form of rocks and, if they manage to get through the protective atmosphere, can hit the surface at such a force that they leave huge craters.
Above is the Barringer Crater in Arizona, USA. It was formed by a meteorite which hit Earth between 25,000 to 50,000 years ago and is 175 metres deep and 1265 metres wide.
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This is the Wolfe Creek crater from Australia. It is 875 metres and 50 metres deep (although it has a "wall" which is 25 metres high above the surface). It is believed that the meteorite that caused this crater hit the surface of Earth 300,000 years ago.
Earth is the most heavily bombarded planet by meteors. However, the craters which are formed from these impacts are nearly always erased through the planet's constant geological, tectonic (the movement of Earth's plates) and weathering processes. There are only about 120 craters recognised on the planet. It is believed that a meteorite or a comet hit the planet's surface 65 million years ago and wiped out the dinosaurs. It is also believed that a meteorite is heading for Earth in 2028.
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