A study by researchers at the University of Bristol in the United Kingdom theorises that a meteor shower 3.9 million years ago was the source of previous metals on the planet Earth.

The basis of that theory is a research made by the team led by Matthias Willbold which took ancient rock samples from southwest Greenland. The rocks formed some of the Earth's earliest crust. Analysis showed that there were distinct differences in concentrations of certain tungsten isotopes in each type.

"This is a sort of 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," Discovery News quoted Mr Willbold.

Metals such as gold, platinum, nickel, tungsten and iridium are attracted to iron, which is what makes up the Earth's core. Based on the metals' properties, it should have moved to the core when the Earth was first formed as a molten mass.

The presence of these metals on the planet's surface supports Mr Willbold's theory that the meteor shower led to the incorporation of these metals into the Earth's outer layer.

When Mr. Willbold's team compared the Greenland samples to rocks from other parts of Earth, they found a 15-parts-per-million difference in an isotope called 182W. The difference supports their theory that the ancient meteorite shower was responsible for the gold and other metals that is behind many industries across the world.

"Our work shows that most of the previous metals on which our economies and many key industrial processes are based have been added to our planet by lucky coincidence when Earth was hit by about 20 billion billion tonnes of asteroidal material," AFP quoted Mr Willbold.