July 23, 2012
Meteorites Hold Secrets Of Earth’s Formation
redOrbit Staff & Wire Reports - Your Universe Online
Scientists attempting to better understand the formation and the present-day layering of planet Earth have turned to ancient meteorites -- meteorites which they say could hold important clues to some of the Solar System's earliest chemical processes.
Those meteorites are known as diogenites, and researchers from the Carnegie Institution, the Scripps Institution of Oceanography, and the University of Maryland studied nine samples (seven from Antarctica and two from the African desert).
Diogenites, they explained, may have come from the asteroid Vesta and are among the Solar System's oldest remaining examples of heat-related chemical processing, Carnegie officials said in a recent statement.
"What's more, Vesta or their other parent bodies were large enough to have undergone a similar degree of differentiation to Earth, thus forming a kind of scale model of a terrestrial planet," they said. "They were able to confirm that these samples came from no fewer than two parent bodies and that the crystallization of their minerals occurred about 4.6 billion years ago, only 2 million years after condensation of the oldest solids in the Solar System."
Their examination focused upon the elements osmium, iridium, ruthenium, platinum, palladium, and rhenium. Collectively, those elements are known as highly siderophile elements, and in theory, when a planet or other large body differentiates enough to form a core, those elements are segregated into that region.
However, previous studies have shown that the mantles of the Earth, Moon and Mars contain more of these elements than they should. The mantles of the Earth and Moon are believed to have formed over 4.4 billion years ago, and Mars's 4.5 billion years ago, meaning that the diogenite samples were formed around the same time, and as such could provide insight as to exactly what might have caused that phenomenon.
"Examination of the samples determined that the highly siderophile elements present in the diogenite meteorites were present during formation of the rocks, which could only occur if late addition or 'accretion' of these elements after core formation had taken place," the Carnegie statement said. "This timing of late accretion is earlier than previously thought, and much earlier than similar processes are thought to have occurred on Earth, Mars, or the Moon."
"Remarkably, these results demonstrate that accretion, core formation, primary differentiation, and late accretion were all accomplished in just over 2 to 3 million years on some parent bodies. In the case of Earth, there followed crust formation, the development of an atmosphere, and plate tectonics, among other geologic processes, so the evidence for this early period is no longer preserved," they added.