FSU geochemist challenges key theory regarding Earth's formation

“According to the late-veneer hypothesis, most of the original iron-loving, or siderophile, elements” -- those elements such as gold, platinum, palladium and iridium that bond most readily with iron -- “would have been drawn down to the core over tens of millions of years and thereby removed from the Earth’s crust and mantle. The amounts of siderophile elements that we see today, then, would have been supplied after the core was formed by later meteorite bombardment. This bombardment also would have brought in water, carbon and other materials essential for life, the oceans and the atmosphere.”

To test the hypothesis, Humayun and his NASA colleagues -- Kevin Righter and Lisa Danielson -- conducted experiments at Johnson Space Center in Houston and the National High Magnetic Field Laboratory in Tallahassee. At the Johnson Space Center, Righter and Danielson used a massive 880-ton press to expose samples of rock containing palladium -- a metal commonly used in catalytic converters -- to extremes of heat and temperature equal to those found more than 300 miles inside the Earth. The samples were then brought to the magnet lab, where Humayun used a highly sensitive analytical tool known as an inductively coupled plasma mass spectrometer, or ICP-MS, to measure the distribution of palladium within the sample.

“At the highest pressures and temperatures, our experiments found palladium in the same relative proportions between rock and metal as is observed in the natural world,” Humayun said. “Put another way, the distribution of palladium and other siderophile elements in the Earth’s mantle can be explained by means other than millions of years of meteorite bombardment.”

The potential ramifications of his team’s research are significant, Humayun said.

“This work will have important consequences for geologists’ thinking about core formation, the core’s present relation to the mantle, and the bombardment history of the early Earth,” he said. “It also could lead us to rethink the origins of life on our planet.”

The researchers’ Nature Geoscience paper is available for purchase or via subscription at www.nature.com/ngeo/journal/vaop/ncurrent/index.html#le.

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