Heat contained in the Earth's crust acts like a life-jacket, and without it much of North America would be under water, suggests research at the University of Utah.

The flooding predicted because of global warming is a much more immediate threat, the researchers note. It would take billions of years for North American rock to cool to the point where it will become denser and sink enough to put much of the continent under water.

The research suggests for the first time that about half the elevation of any place in North America is related to temperature differences within the Earth's crust, with most of the rest due to differences in what the rocks are made of.

"To estimate the amount of heat within the lithosphere — crust on upper mantle — we use, for each region, 10's to 100's of measurements of temperatures within the upper 100-plus metres of the Earth," explained Derrick Hasterok, a University of Utah doctoral student.

"By measuring temperature with depth, we can extrapolate temperatures throughout the entire crust and upper mantle."

While people widely understand how shifts in the Earth's tectonic plates result in the creation of mountains or sinking of the ocean floor, most people don't realize those tectonic forces act along with the composition and temperature of rock.

As the crust's plates collide to form mountains, the mountains rise because the collision makes less dense crustal rock get thicker and warmer and therefore more buoyant.

Some of the heat they identified comes from deep within the Earth, but the decay of radioactive elements also contributes.

"Canada really popped out on this," said Hasterok.

"Our method also helps to identify regions like the plains regions of northern Canada that have high upper crustal radioactivity — concentrations of uranium, thorium, and potassium."

"The reason we can identify high concentrations of radioactivity is because the decay of these radioelements increases temperatures only in the upper part of the crust, thereby inflating our estimates of average lithospheric temperatures in these regions," said Hasterok.

"Because elevation responds to the average temperature of the lithosphere, not just the top, these regions appear hot and lower than we would otherwise suspect."

While the research doesn't mean the earth is likely to shift anytime soon, Hasterok said, "it helps in understanding the dynamics of the planet and how the planet is evolving."

The research was published in the June online issue of Journal of Geophysical Research-Solid Earth.