A meteorite is a rock from space. They’re a reminder of our place in the universe, and they provide clues as to where we come from and to the origins of the solar system.
Every day over a hundred tonnes of material rains down on the Earth; sometimes you might be lucky enough to see it happening. This occurs when a meteoroid, which is what we call a rock in space, crashes through the Earth’s atmosphere. As it does so, it heats the surrounding air and it glows, causing a brilliant streak of light, and what we also call a meteor. Some people call it a shooting star but they’re not stars at all. Meteoroids are normally fragments from asteroids, sometimes from comets, and sometimes even they’re chunks from the Moon or Mars. Most meteoroids are really small; they’re about the size of a pea, or even smaller like a grain of sand. But sometimes much larger meteoroids can come crashing down onto Earth and they can survive the fiery descent through our atmosphere.
Some estimates say that about once a year a meteoroid with the energy of an atomic bomb crashes through and lands on Earth, but most of the time we don’t get to know about it. This is because they often land in the ocean or somewhere uninhabited and we don’t find out. But when one lands nearby, they really do cause quite a stir.
This happened in 1954, in Alabama in the US, where a housewife, by the name of Ann Hodges, was having a nap in the afternoon on her couch and a meteorite crashed through the ceiling, it bounced off some furniture, before hitting her in the hip. She was OK but I think she ended up with quite a bad bruise.
But meteorites don’t even have to land to cause a lot of trouble. In 1908, it’s thought that a large asteroid, or maybe even a comet, exploded over the skies of Tunguska, which is an uninhabited remote region of Siberia. No impact crater was formed but the trees in an area of about 50 kilometres across were completely flattened, and the sound was actually heard half the world away in London.
Australia has about 20 known impact craters and the most famous of them all is the Wolf Creek crater in Western Australia. It’s the second most perfect crater in the world and in fact it was used by the Apollo astronauts as a training ground so that they could get a feel for what Moon craters might be like. The crater is about 900 metres wide and about 60 metres deep. We think that is was created about 300 000 years ago by a 50 000 tonne meteorite.
And of course, it was 65 million years ago, a very large asteroid smashed into Mexico’s Yucatan Peninsula. The sky was filled with the debris, blocking out the sun, and this changed the environment, which ended up making the dinosaurs go extinct. To cause a mass extinction, an asteroid needs to be larger than about six kilometres, and it’s predicted that such an object would collide with Earth about once every hundred million years. So what we need to do is to be watching the skies, looking for any such rogue objects, and then to be prepared to take action if we found one that was on a collision course with Earth.