Precious metal arrived our planet in a 200 million-year long meteor shower that battered the Earth 3.9 billion years ago, scientists revealed in a new research.
Geologists at the University of Bristol believe they have proven that precious metals on Earth including gold and platinum have come from outer space, when a mammoth meteorite shower struck the Earth 650 million years after its formation.
The puzzling presence of precious metal in Earth's mantle and crust may be explained once the mysteries of Earth's formation, dating back to 4.5 billion years ago, are solved. As magma cooled down and denser material sank toward the core of the planet, the iron-loving gold should have retreated toward the core and left barely no trace on the surface.
However, tens of thousands of times more precious metals are found in the Earth's crust than supposed.
To find out the source of the precious metals, Dr. Matthias Willbold and professor Tim Elliott of the Bristol Isotope Group in the School of Earth Sciences 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 predating the meteor shower.
The ancient rock contained a marginally higher ratio of the tungsten isotope 182W than more modern rock. The tungsten isotope was produced in the first 50 million years of the solar system, signifying that meteor shower had altered the composition of Earth's surface.
Scientists believe that 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 billion tonnes of asteroidal material.
The research was published in the latest journal Nature.