Comets Asteroids Craters are formed by meteorites hitting the Earth. Geologists and astronomers study meteorites and their craters, to piece together the conditions that prevailed 4.5 billion years ago. There are two types of crater, simple and complex .
Simple craters are the most recognisable as they have a distinct bowl shape and a raised outer rim.
Complex craters are quite different in that they have a raised central peak surrounded by a trough and fractured rim. These craters are often 100 times wider than they are deep. Most of the large craters have disappeared due to millions of years of geological activity and weathering by wind and rain. Nearly all the craters that we see today are either very young or were too large to erode completely. Spider is a complex crater in Western Australia.