Meteorite Shower Brought Gold to Earth, Scientists Believe

 @ibtimes
on September 08 2011 12:57 AM

Gold aficionados must thank meteorites for bringing the precious metal to Earth almost 4 billion years ago.

 According to a new research, precious metals arrived on the Earth when a cataclysmic meteor shower pounded our planet 3.9 billion years ago.

Geologists at the University of Bristol believe they have proven that precious metals on Earth, including gold and platinum, are the result of a 200-million-year long mammoth meteor shower that occurred 650 million years after Earth's formation.

The Earth was a huge ball of magma when it first formed approximately 4.5 million years ago. As the planet cooled, denser material sank toward the center, eventually producing a core made mostly of iron.

Certain metals like gold, platinum, nickel, tungsten and iridium, which are attracted to iron, should have migrated to the core, leaving the outer layers of the Earth stripped of its precious metals. Yet tens of thousands of times more precious metals are found in the Earth's crust than the theory would suppose.

Several theories have been proposed to explain this mystery, with the latest one suggesting that the presence of abundant amounts of gold and other precious metals is due to a massive meteor shower that struck Earth well after the core had formed.

To corroborate this theory, Matthias Willbold and Tim Elliott of Bristol University analyzed 3.8 billion-year-old rock samples from the Isua Greenstone Belt in Greenland. The mantle source where these rocks are coming is from 4.5 billion years ago, according to Willbold, suggesting its chemical signatures predate the meteor shower.

The ancient rock samples from Greenland contained a marginally higher ratio of the tungsten isotope 182W compared to more modern rock. Tungsten 182 was produced only in the first 50 million years of the solar system, signifying that meteor shower had altered the composition of Earth's surface.

Scientists believe the meteorites were stirred into the Earth's mantle by big currents in the molten material, leading to the concentration of the precious metals in ore deposits to be mined today.

Extracting tungsten from the rock samples and analyzing its isotopic composition to the precision required was extremely demanding given the small amount of tungsten available in rocks, said Willbold.

Our work shows that most of the precious metals on which our economies and many key industrial processes are based have been added to our planet by lucky coincidence when the Earth was hit by about 20 billion tons of asteroidal material. 

The research was published in the latest issue of the journal Nature.  

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