The Driest Place on Earth.
It's not where you expect. You're thinking of majestic sand dunes along the western edge of the Sahara, or the barren rocky outcrop's of Chile's Atacama desert. The driest place on Earth is in Antarctica: the McMurdo Dry Valleys. Antarctica has been covered in ice for the last 15 million years, and has built up an average ice thickness of 1.9km. The entire continent is cold (as low as -90ºC) and as dry as most deserts on Earth (South Pole average precipitation is 10cm/year). The McMurdo Dry Valleys are even drier. The fact that they have remained ice free, while the rest of the continent has built up thousands of meters of ice over millions of years, tells you just how parched these valleys are.
Their annual average precipitation is zero cm. They are found in the rain shadow of the 1.6km high Transantarctic Mountains. These mountains also act as a barrier to prevent glaciers from flowing into the valleys. Any ice that does form in the valleys rapidly 'sublimates', evaporating directly from solid ice to water vapour without melting. This processes is helped along by bone-dry 'katabatic winds', which form as cold dense air literally falls off the surrounding ice sheets, and rips through the valleys at over 300 km per hour.
Animals that stray too far into the valleys quickly die of dehydration. Rather than rotting, the dry air desiccates and mummifies their bodies, which can be preserved on the valley floor for hundreds or thousands of years (like the seal in the photo). When the explorer Robert Scott discovered these valleys in 1903, he called them the 'valleys of death'.
Since 1903 scientists have had a closer look at the dry valleys, and they are far from dead. All kinds of 'extremophiles' (life that thrives in extreme environments) call the McMurdo valleys home - lichens, mosses, nematodes (microscopic worms) and other microbes are most common.
These frozen deserts are one of the best analogues we have for Martian environments. Studying how life survives there is one of our best ways of understanding how life might exist on other planets.
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Image Source: - Bull Pass: http://goo.gl/E15f19 - Mumified Seal: http://goo.gl/TtIoqe
Where are these dry valleys?: http://goo.gl/CCnTSd A bit more about them: http://goo.gl/Mj1ZvU The wettest place on Earth: http://goo.gl/7Ge5lE We've talked about these valleys before: http://goo.gl/pAHkY9
