The Earth formed about 4.5 billion years ago. Since then it has developed from a sea of molten rock into the complex environment we live in today, its landscape transformed again and again over countless millennia by repeated cycles of geological change.
Mountain ranges have risen and been worn down; continents have formed and been torn apart; vast, planet-encircling seas have been born and died. Ice ages have come and gone, and lush jungles have disappeared under polar icecaps.
Each of these changes has left its mark, recorded in layer upon layer of different kinds of rock. By comparing the layers in different places, geologists can accurately recreate the landscape’s history.
Examining the fossilised plants and animals found in each layer, we can understand the history of life – not just what a living thing was like, but precisely when it lived, what it evolved from, and what its descendants became in turn.
This is called the ‘fossil record’, and it shows that life on Earth started about 3.8 billion years ago. Complex organisms emerged only about 600 million years ago, and modern humans just 200,000 years or so. So seen on the planet’s timescale, our species’ whole lifespan is a fleeting moment.
Like our own history, the story of the Earth is divided into distinct periods. These span vast stretches of time, and are usually divided by some major event. For example, the Cretaceous period 65 million years ago came to a crashing end when a large meteor collided with the Earth leading to the extinction of the dinosaurs and many other species.
The dinosaurs ruled the planet for more than 160 million years. Compared with this, our own time on Earth is minuscule. But we stand out from the rest of nature in terms of our ability to affect our environment on a planetary scale.
The changes we are making reach every part of the world and every aspect of its environment, and they’re happening at a speed that has no parallel in history. This is why scientists are calling the new epoch we’re living in the Anthropocene – or more colloquially (but incorrect), the human age.
The magnitude of disturbance that a system can tolerate before it shifts into a different state. The capacity of a system to absorb disturbance and reorganize while undergoing change so as to still retain essentially the same function, structure, identity and feedbacks.