Continents loss to oceans boosts sta...( HOUSTON April 1 2008 -- New research...)

HOUSTON, April 1, 2008 -- New research suggests that the geological staying power of continents comes partly from their losing battle with the Earth's oceans over magnesium. The research finds continents lose more than 20 percent of their initial mass via chemical reactions involving the Earth's crust, water and atmosphere. Because much of the lost mass is dominated by magnesium and calcium, continents ultimately gain because the lighter, silicon-rich rock that's left behind is buoyed up by denser rock beneath the Earth's crust.

The Earth's continents seem like fixtures, having changed little throughout recorded human history. But geologists know that continents have come and gone during the Earth's 4.5 billion years. However, there are more theories than hard data about some of the key processes that govern continents' lives.

"Continents are built by new rock that wells up from volcanoes in island arcs like Japan," said lead author Cin-Ty Lee, assistant professor of Earth science at Rice University. "In addition to chemical weathering at the Earths surface, we know that some magnesium is also lost due to destabilizing convective forces beneath these arcs."

Lee's research, which appeared in the March 24 issue of the Proceedings of the National Academy of Science, marks the first attempt to precisely nail down how much magnesium is lost through two markedly different routes -- destabilizing convective forces deep inside the Earth and chemical weathering reactions on its surface. Lee said the project might not have happened at all if it weren't for some laboratory serendipity.

"I'd acquired some tourmaline samples in San Diego with my childhood mentor, Doug Morton," Lee said. "We were adding to our rock collections, like kids, but when I got back to the lab, I was curious where the lithium, a major element in tourmaline, needed to make the tourmalines came from. I decided to measure the lithium content in the granitic rocks fro
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