THE ULTIMATE VARIETY SHOW

Planet Earth is home to an extraordinary range of life, differing wildly between continents. Scientists have wondered for centuries how our natural world came to be so diverse, yet interconnected. And now we know that the mystery can be explained by a dinosaur called mesosaurus.

With its long, thick tail, powerful jaws and stumpy, frog-like legs, mesosaurus was a strange creature – like a newt the size of a small crocodile, living in freshwater lakes 280 million years ago. But the strangest thing about mesosaurus is that its fossils have been found on both sides of the Atlantic. Clear evidence of this early underwater reptile has been found in southern Africa as well as in South America.

How can this be? There was no way it could swim across the south Atlantic. So why are its fossils found on two continents, 4,000 miles apart? The answer is that Africa and the Americas were once one, along with all the land mass on the planet – one supercontinent called Pangaea. But about 200 million years ago, it was ripped in two and then began to break up into the seven ‘worlds’ we know today – North and South America, Europe, Asia, Australasia, Africa and Antarctica.

That’s why, if you look at a map, the western bulge of Africa looks as though it would fit neatly into the Caribbean, between the Americas. Once upon a time it did. This was discovered by German geophysicist Alfred Wegener in 1912, but his theory of ‘continental drift’ proved controversial for 50 years... until mesosaurus turned up.

Continents drift because of the molten magma bubbling up from the centre of the Earth at the boundaries between plates. Our planet’s skin is a moving jigsaw puzzle, continually in motion – Australasia, for example, is moving north at 7cm a year and will eventually smash into south-east Asia.

As the continents broke apart, the plants and animals on them began to evolve separately, each adapting to its own environment. The continents developed their own terrains and climates, and with these their own unique flora and fauna. If Pangaea had remained whole, we wouldn’t have the stunning variety of life on Earth we have today.

Seven Worlds, One Planet, a breathtaking seven-part series from the BBC’S Natural History Unit narrated by Sir David Attenborough, celebrates that variety. Earth is more diverse than we could imagine... and this astonishing show helps us understand how wild it really is. n

Lightning flashes over the desert in the south-west US