IF EARTH鈥橲 interior were to cool down, New York and Los Angeles would end up hundreds of metres under water. North America, it seems, is being kept afloat by the heat beneath the continent.
Derrick Hasterok and David Chapman at the University of Utah in Salt Lake City were studying how bumps form in the Earth鈥檚 crust and upper mantle. One cause for the differences in elevation is the buoyancy of rocks: the less dense the rock, the higher it rises. Until now it had been assumed that density varied only according to the type of rock.
Hasterok and Chapman created models of North America to see if temperature also had a part to play in altering the rocks鈥� density. By accounting for the effects of rock type and thickness they were able to determine how much of a region鈥檚 buoyancy comes from expansion caused by heat.
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鈥淚t turns out about half of the elevation is due to temperature,鈥� says Hasterok. The heat comes from Earth鈥檚 interior, tectonic plate movement and the decay of radioactive elements in the crust. Without the heat, much of North America would be submerged. Even Denver, the 鈥渕ile-high city鈥�, would lie 222 metres below sea level (Journal of Geophysical Research, vol 112, p B06414).
