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Saturday, May 12, 2007

Satellites solve mystery of low gravity over Canada

If it seems Canadians weigh less than their American neighbours, they do – but not for the reasons you might think. A large swath of Canada actually boasts lower gravity than its surroundings.

At first, researchers suspected it was due to an ice sheet called Laurentide that blanketed a sizeable chunk of North America during the last ice age. In places, the sheet was more than 3 kilometres thick, and it depressed the Earth's crust beneath it.

When the ice age ended about 20,000 years ago, the ice rapidly melted. But the crust has been springing back much more slowly, and it is rebounding today by about 12 millimetres per year.

But in the last decade or so, scientists have begun to suspect that convection in the Earth's mantle, a layer of hot, flowing rock beneath the crust, also plays a role.
The sludge-like mantle rises and falls in plumes as it is heated from below and cooled from above. The mantle can drag the overlying tectonic plates with it as it moves.

Source & Iamge:
newscientis

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