A new study shows that most of the gold and other precious metals found in Earth today came from a barrage of meteorites that pummeled Earth 3.9 billion years ago.

The research from a group of scientists led by Dr. Matthias Willbold from the University of Bristol reveals why there is an abundance of minerals on the surface of the planet rather than in the center of the Earth. Certain metals like gold, platinum, nickel and other 'iron-loving' metals should have sunk to the planet's iron core 4.5 billion years ago, leaving only lighter silicates on the surface.

This state of affairs has puzzled geologists who have attempted to explain why the Earth is so rich with these metals. Dr. Willbold's team theorizes that this abundant cache of precious metals is because of a huge meteor storm that hit the Earth 3.9 billion years ago and littered the crust with the metals.

The heavy meteor shower added between a half and one percent of additional material to the Earth. The metals eventually became incorporate in the crust to be mined by humans ages later.

The research published in the journal Nature, provides evidence of the team's hypothesis. Willbold and colleagues examined ancient rock samples from southwest Greenland that predate the supposed meteorite bombardment and compared them with volcanic plume samples from places like Hawaii that represent the modern mantle.

The team found a distinct difference in the concentration of tungsten isotopes from before the bombardment and after the bombardment.

"This is a sort of a time capsule that gave us the possibility to calculate how much material had to be added to the Earth to satisfy the tungsten isotopic composition that we find in the Earth today," Willbold said.

"It is so far the best isotopic or geochemical evidence that late bombardment ever happened," he added.

"All the precious metals that we find today -- and probably also water -- have been introduced to the accessible Earth from these late stage meteorites," Willbold said.