On Christmas Eve 1968, the Apollo 8 astronaut William Anders took a photograph of the view outside the window as his spaceship orbited the moon. The now iconic Earthrise image shows our half-moon blue planet under a decoration of clouds rising from the blackness of space over the lunar surface.
The picture encapsulated Earth’s precariousness in the cosmos and, for many, contained a message of humility and stewardship for our home.
We’ve had Earthrise and images like it from the Apollo missions for half a century now. But suppose some aliens had been viewing our planet for its entire 4.5bn-year history. What would they have seen?
Over nearly all that immense time, changes would have been very gradual: continents drifted; the ice cover waxed and waned; successive species emerged, evolved and became extinct during a succession of geological eras.
But visible change has accelerated rapidly in the past few thousand years – a tiny sliver of the Earth’s history. Now geologists have decided those changes have been so profound, so global and so permanent that our catalogue of the Earth’s history needs to change accordingly. Since the last ice age, around 11,000 years ago, human civilisation has flourished in the climatically benign Holocene. Now they believe that epoch has come to an end and we have entered a new human-influenced age, the Anthropocene.