Thursday, 17 March 2011

Here comes the sea

On the shelf at the back of the shop there are some Mesosaurus brasiliensis fossils. Mesosaurs were long-necked reptiles that lived in freshwater lakes in the Early Permian. Big deal? The important thing about mesosaurs is exactly where they were found. Finds of the same age in Southern Africa and Eastern South America were one of the first signs of continental drift and plate tectonics in general. They had been swimming in lakes which had formed in rift valleys as the supercontinent of Gondwanaland began to pull apart.

Plate tectonics has been big news of late, sadly, with earthquakes causing horrendous destruction and tens of thousands of deaths in Japan and New Zealand. It may not make the news all the time, but it is happening all the time. The Earth's surface is comprised of a group of plates which are moved around by the convection currents created in the molten rock of the core beneath them. The relationship between the plates is complicated but their constant movement has shaped the face of the planet - the atlas would look very different were it not for continental drift. Far more is known about the processes involved now than even a few decades ago. David Attenborough remembers a skeptical geology lecturer dismissing the idea when he was at university. There is still a lot to be learned about how the plates interact, though. A fuller understanding may help seismologists predict earthquakes over the longer term, so it's an area that deserves to see a lot of research.

Africa and South America parted ways some 200 million years ago, but in Eastern Africa a similar process is happening right now. The Rift Valley in Ethiopia is a depression caused by the pulling apart of the continental crust as - very slowly - a new ocean is formed. It's not like you need worry about having to buy a new map or anything; it's going to take quite some time. In geological terms, though, the separation is happening pretty quickly, and the volcanoes and earthquakes are a sign of what's happening not far below the surface.

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