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5 December 2013 11:26 am ,
Vol. 342 ,
At age 30, Dutch biologist Freek Vonk has built up a respectable career as a snake scientist. But in his home country,...
Since arriving on the island of Guam in the 1940s, the brown tree snake ( Boiga irregularis ) has extirpated native...
An animal rights group known as the Nonhuman Rights Project filed lawsuits in three New York courts this week in an...
Researchers have been hot on the trail of the elusive Denisovans, a type of ancient human known only by their DNA and...
Thousands of scientists in the Russian Academy of Sciences (RAS) are about to lose their jobs as a result of the...
Dyslexia, a learning disability that hinders reading, hasn't been associated with deficits in vision, hearing, or...
Exotic, elusive, and dangerous, snakes have fascinated humankind for millennia. They can be hard to find, yet their...
Researchers have sequenced and analyzed the first two snake genomes, which represent two evolutionary extremes. The...
- 5 December 2013 11:26 am , Vol. 342 , #6163
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Dating the Scum of the Earth
24 January 1997 (All day)
By 2.7 billion years ago, the cooling Earth had formed a crust of continental rock about as thick as today's terra firma. The finding, reported in today's Science,* appears to solve a long-running mystery of when the ground we live on formed.
The crust congeals from molten rock that wells up from the mantle, cools, and thickens. It's "a thin scum on top of the mantle," says geochemist Albrecht Hofmann of the Max Planck Institute for Chemistry in Mainz, Germany. Geologists understand the mechanics of crust formation, but they have had little idea whether most of it formed at once or over billions of years.
Clues to the early history of the planet's surface come from the crust's composition: It's enriched in niobium and uranium, elements deposited by cooling magma. Paul Sylvester and colleagues at Australian National University in Canberra argue that the relative abundances of the two elements in the crust and magma at different points in Earth's history can indicate when and how much crust was formed on ancient Earth. They discovered that basalt rock formed from the mantle 2.7 billion years ago in Western Australia has roughly the same concentration of niobium and uranium as mantle rock formed more recently--meaning that the amount of Earth's crust then was probably the same as now. "We think that a significant amount of crust was already extracted from the mantle 2.7 billion years ago," says Sylvester.
"It's a great observation," says Harvard geologist Roberta Rudnick, who liked the approach of measuring niobium and uranium levels. She says, however, that she has qualms that the basalt samples may have been contaminated with uranium that had migrated from crust. "But this is the sort of way we're going to find out when the crust separated from the mantle," she says.