Published: December 6, 2017, 8:12 p.m.
A large planetary body the size of the Moon penetrated to the Earth's core during the first days of the formation of our home planet, delivering in the process precious metals like gold and platinum, suggests a new study. The team determined that the total amount of material delivered to Earth could have been two to five times greater than previously thought, and the impacts profoundly altered the Earth by depositing familiar elements such as gold.
"These results have far-reaching implications for the formation theories of the Moon and beyond," said Simone Marchi of the Southwest Research Institute in the United States. "Interestingly, our findings elucidate the role of large collisions in the delivery of precious metals such as gold and platinum found here on Earth," Marchi added. Planetary collisions are the nucleus of the formation of our solar system. Scientists have believed for a long time that after the formation of the Moon, the primitive Earth experienced a long period of bombardment that decreased about 3.8 billion years ago.
During this period, called "late accretion," collisions with planetary bodies the size of the Moon, known as planetesimals, embedded large amounts of metals and mineral-forming rocks in the mantle and crust of the earth. It is estimated that approximately 0.5 percent of the Earth's present mass was delivered during this stage of planetary evolution. The new study confirms how massive collisions released metal to Earth.
With the support of NASA, researchers from the Southwest Research Institute and the University of Maryland created high-resolution impact simulations that showed significant portions of the nucleus of a large planetesimal that could penetrate the path down to merge with the core of the Earth, or bounce back into space and escape from the planet completely. The study published in the journal Nature Geoscience found evidence of more massive accretion on Earth than was thought after the formation of the Moon.
The abundance of the mantle of certain trace elements such as platinum, iridium and gold, which tend to bind chemically with metal iron, are much higher than would be expected as a result of core formation. This discrepancy can be explained more easily by the late accretion after core formation was completed, according to the study.
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