Comets and life



New simulations suggest that large amounts of the organic molecules needed to form the first life on Earth could have been brought by comets that bombarded the planet early in its history. The models show that comets of moderate size would have slowed down enough during entry into Earth's atmosphere for their organic component to survive the impact intact.

The chemical precursors to carbon-based life are thought by many scientists to have been compounds such as hydrogen cyanide (HCN), essential for formation of amino acids and DNA, and formaldehyde (H2CO), a building block of simple sugars. The source of these and other compounds is not known with confidence: photochemical reactions in the young Earth's CO2-rich atmosphere may have created 1020–1021 g of hydrogen cyanide and formaldehyde from 4.3 to 3.7 billion years ago, but these processes are highly dependent on the composition of the primordial atmosphere, which is not well known.