The Archaean planet

Abstract

St John’s gospel starts with the words ‘In the beginning’. Transliterated from the Greek this reads as ‘En Archi’, or ‘In the Archaean’: this English name is taken from the Greek source to describe the beginning of the geological record and the pervasive influence of life on Earth. As yet we have no agreed definition of when the Hadean (the accretionary period), ended and the Archaean began. We could use the beginning of the geological record, at present set at about 4.3 billion years for the oldest minerals, or around four billion years for the oldest rocks, or we could define the onset of the Archaean as the time when the first replicating organisms occupied the seas. Life — including rabbits — breeds very fast in an open environment until it completely exploits the available food supply in whatever ecological niche it occupies. Once a photosynthetic bacterium had evolved, within a handful of years the seas would be filled with bacteria in the same way that Australia, a handful of years after colonization, is now widely occupied by rabbits. The onset of life is the great divide in the history of the planet. When life began, when our most distant ancestor was born, this planet became different, perhaps unique.