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Key theory regarding Earth's formation challenged

Written by: Staff

Washington, May 2 : A Florida State University (FSU) researcher has challenged a key theory regarding the Earth's formation, and some of the physical processes that helped shape the Earth as we know it today.

The researcher, Munir Humayun, is an associate professor in FSU's Department of Geological Sciences and a researcher at the National High Magnetic Field Laboratory.

In a paper published in the science journal Nature Geoscience, Humayun has given a direct challenge to the popular "late veneer hypothesis," a theory which suggests that all of our water, as well as several so-called "iron-loving" elements, were added to the Earth late in its formation by impacts with icy comets, meteorites and other passing objects.

"For 30 years, the late-veneer hypothesis has been the dominant paradigm for understanding Earth's early history, and our ultimate origins," said Humayun.

"Now, with our latest research, we're suggesting that the late-veneer hypothesis may not be the only way of explaining the presence of certain elements in the Earth's crust and mantle," he added.

According to the late-veneer hypothesis, the amounts of siderophile elements that we see today, 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.

According to Humayun, "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."

"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," he added.

The potential ramifications of the team's research are significant.

"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," said Humayun. "It also could lead us to rethink the origins of life on our planet," he added.


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