Abstract

Astronomical observations of star-formation regions show that many young stellar objects are accompanied by dusty disks. These disks may evolve into planetary systems. The Sun, the Earth and other planets, along with asteroids, comets and other minor Solar System bodies formed in this way from a collapsing cloud of gas and dust (the pre-solar nebula). Gradual accretion of dust into proto-planetary bodies was accompanied by aggregation, collision, break-up, re-aggregation, melting and differentiation of material in a complex history of planetary build-up. The final turbulent stages of Solar System formation were traced out by intense cratering of the planets by asteroids and comets. The surface of the Earth was inimical to life, heated and melted during bombardment. It is probable that during this period of the Earth’s history, an atmosphere built up and was stripped away more than once, in a cycle of increasing stability punctured by episodes of bombardment. Gradually, however, the inner Solar System became more quiescent; the Earth’s surface cooled; its atmosphere was retained; oceans formed and conditions were set to allow life to emerge. This stage is the interface between the geological and biological history of the Earth, when simple molecules formed more complex systems, which in turn became single-celled organisms.

The pathway from astronomy to biology can be traced through study of comets and meteorites, primitive bodies of dust and ice that survive from the earliest era of Solar System formation.