Learn · Places · 6 minute read
Britain’s long journey
The ground under Britain began near the South Pole, in two pieces, on two continents. Here is the route it took.
Stand anywhere in Britain and the rock under your feet has travelled further than you ever will. The plates of the Earth's surface move a few centimetres a year. Over hundreds of millions of years that adds up to thousands of kilometres. The ground that is now Britain has crossed most of the globe, from the cold south, over the equator and up into the north.
Geologists work out where a rock formed in two main ways. Some rocks keep a faint record of the Earth's magnetic field, which points at a steeper angle nearer the poles. And the rocks themselves are clues: coral reefs grow in warm tropical water, dunes of wind-blown sand form in deserts, and coal comes from swamp forests.
Two halves of a country
Scotland and England began on different continents. Scotland was on the edge of Laurentia, the continent that became North America and Greenland. England and Wales were on Avalonia, a strip of land that had broken away from the great southern continent. Between them lay the Iapetus Ocean.
Avalonia drifted north and the ocean narrowed, its floor sinking under the continents on either side. By the Silurian period, more than 400 million years ago, it had closed completely. The join, called the Iapetus Suture, runs roughly under the Solway Firth. The collision squeezed, folded and lifted the rocks on both sides, and you can still see that folding in the Southern Uplands and the Lake District.
The rocks keep the diary
Each stage of the journey left a different kind of rock behind, and you can still visit them. The pale limestone of the Peak District and the Yorkshire Dales formed in clear, warm seas when northern England sat near the equator. Later in the Carboniferous, swampy forests grew on deltas and were buried, and became the coal that powered the Industrial Revolution. In the Permian and Triassic, Britain lay in the dry belt north of the equator, and the red sandstones of the Midlands, Devon and the Eden Valley are its fossil deserts. Later still, warm seas returned and laid down the chalk of the south coast cliffs.
The Jurassic Coast in Dorset and East Devon shows about 185 million years of this story in one stretch of cliffs, from Triassic deserts through Jurassic seas to Cretaceous chalk.