A meteorite travelling 55,000 kilometres per hour smashed into the earth here eons ago, blasting a hole 244 metres deep and 2.5 kilometres wide. Aerial photographs revealed the crater in 1955, and since then scientists have pieced together much of its geological history. Analyses of drill samples suggest that the meteorite struck in the late Precambrian or early Cambrian period (between 450 and 650 million years ago). At first the depression filled with water becoming a circular lake. Later Palaeozoic seas swept in sediments filling the crater to its present depth of about 30 metres. The explosive impact of the meteorite (estimated to have been only 90 metres in diameter) is still evident in the hundreds of feet of shatterd rock that drilling has detected beneath the original crater floor.