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Rocks and genes tell the same story

By , 19 September 2017

A map of a world where all the land is connected into one blob.

180 million years ago, the world was a very different place.
Image: Wikimedia commons/LennyWikidata, David Shaw remix

The rocks beneath your feet tell an amazing story. Back when dinosaurs roamed the land, all the continents of Earth were joined together in a supercontinent we call Pangaea. But it wasn’t to last. About 180 million years ago, Pangaea started to split apart – first into two, and then into smaller and smaller pieces. Eventually, these smaller pieces moved to form the continents we know today.

Well, that’s the story that geologists tell. But is there any way to make sure they’re right? Researchers from the Australian National University have been piecing together the same story from a much livelier source – DNA.

The idea is surprisingly simple. When the continents were joined together, dinosaurs (and mammals and reptiles…) were free to wander about and spread their genes. When the world split in two, animals on one half could no longer meet and mate with their friends over the ocean. Mutations in one population never made it to the other, and eventually these changes in DNA built up. By counting the differences in the DNA of two species, scientists can estimate how long ago this split happened.

The researchers analysed more than 500 species, and found that DNA told the same story as the rocks. The breakup of Pangaea started around 180 million years ago, and in almost every breakup from then on, the dates lined up. (The only place the team couldn’t test was Antarctica, because it didn’t have any animals to test!). The scientists found they could even calculate when continents collided – such as the joining of India and Asia, around 50 million years ago.

For scientists, it’s very satisfying that DNA and rocks tell the same story. It means the geologists were right all along. And biologists can use their new DNA techniques to work out other interesting dates, too!

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