Imagine, if you will, a calm, peaceful day in the middle of a shallow sea 1.8 billion years ago in the area of Sudbury Ontario. There was very little in the way of life on the planet, and what was there was mostly tiny life-forms somewhat akin to the bacteria of today. There would be little recognizable in the landscape due to the changes that the earth has undergone due to the shifting of the continents.
Suddenly, everything would have changed. Coming down from the sky, a large comet composed of water, dust, and rock strikes the planet with incredible force. This comet, between 10 and 16 kilometres across would have struck the planet at speeds of tens of kilometres per second, hardly even noticing the earth’s atmosphere as it plunged into the ground, deforming the earth’s crust up to 16 kilometres below the surface, creating a crater more than 250 kilometres across.