The impact of impacts

Adrian Boyce and John Parnell examine whether traces of life be found in the harshest conditions on Mars. The Haughton impact crater lies in the wilderness of the Canadian High Arctic on Devon Island - the largest uninhabited island on Earth. Nearly 40 million years ago, a meteorite two kilometers across crashed into Earth, leaving behind a 23km-wide crater in the bedrock and causing serious damage over an area of 50km ². The rocks the meteorite encountered were mainly ancient carbonates, around 470 million years old, but they also contained thick beds of sulphate salts, called gypsum. These are the remnants of ancient seas and lakes that dried up, of which there are many examples through geological time. The occurrence of sulphate also sparks an intriguing possibility. Sulphate is at the heart of one of the oldest and most important biological metabolic functions on Earth - bacterial sulphate reduction.