The Earth, as it was

Every map here is a reconstruction. Geologists work out how each plate has moved from the rocks: the magnetism frozen into them when they formed, the stripes of the ocean floor, and the fossils and mountain belts that match up across today’s oceans. A plate model puts all of that together and winds it back.

The land you see is today’s coastline, moved back to where its plate was. It is not the shoreline of the time. Sea level rises and falls (in the last ice age alone it fell by 134 metres, see Ice ages), and the edges of the land change, so the real ancient coasts were different. The shapes are there to help you recognise where things were. The same goes for today’s borders and your town: they show where that patch of ground was, not anything that existed then.

The further back you go, the less certain the map. We use a model whose builders fixed its plates to the Earth with rock magnetism. Models built on other methods agree closely for recent times, but they drift further apart the further back you go, especially before about 252 million years ago, in the Paleozoic and earlier.

The fossil finds

The finds come from the Paleobiology Database, where researchers record every published fossil find with its place and the age of its rock. That includes some old identifications that experts now doubt, such as teeth once put down to a famous dinosaur far from where its skeletons are found, so a dot shows where a find was recorded, not proof the animal lived there. Each find is shown at the moment on the globe nearest that age, if one is within 25 million years, so the animals shown together did not all live at once, and moved with the same plate model as the land. So a dinosaur shown at 150 million years ago may have lived 20 million years before or after. A few old records give a dinosaur an age far from the Natural History Museum’s dates for it, often because the fossil has since been given another name, so we leave out finds that disagree with the museum by more than 10 million years. Three of our 326 dinosaurs are not shown: Fukuisaurus and Nipponosaurus were found in Japan, where the model has no plate under those spots at their time, and the finds of Cedarpelta are dated younger than the museum’s dates for it.

Names, climate and sea level

The names of the old continents and oceans are the ones geologists use, from Torsvik and Cocks’s Earth History and Palaeogeography. They are placed on a spot that belonged to each one, so they move with it; the oceans are labelled between their shores. Old continents had no hard edges, so treat the labels as a guide.

The temperatures are averages of Christopher Scotese’s maps of the world’s climate through the last 540 million years, which combine a climate model with evidence from the rocks: coal, salt, desert sand and the scratches left by glaciers. A newer study by Emily Judd and others (2024), using different methods, finds the same pattern of hothouses and ice ages but bigger swings, from 11 to 36 °C. Nobody has a reliable global temperature from before about 540 million years ago. Sea level is harder still: geologists can tell when the sea rose and fell much better than by how much.