A gold rush: Earth's precious minerals formed when another world collided with our planet 4.45 billion years ago

It was previously thought that minerals formed in a series of minor impacts
Computer simulations were used to track Earth's first 300 million years
The results suggest that a single impact with another world caused the minerals to form in one go

Published: 07:27 EST, 11 October 2016 | Updated: 09:09 EST, 11 October 2016

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It has long been believed that Earth's precious metals, such as gold and platinum, formed on the planet over the course of several minor impacts.

But new research is challenging this theory, and suggests that a single huge collision with another world could be responsible for the precious metals.

The findings suggest that Earth's history could have been less violent than previously thought.

It has long been believed that Earth's precious metals formed on the planet over the course of several minor impacts. But new research is challenging this theory, and suggests that a single huge collision with another world could be responsible (artist's impression)

EARTH'S PRECIOUS METALS

Earth has an unusually high proportion of precious metals near the surface, which is surprising, as they would usually be expected to settle down near the core of the planet.

Until now, this has been explained by the 'late veneer' theory, which suggests that foreign objects hit Earth, and in the process deposited the precious metals near the surface.

The computer simulation took into account the metal concentrations on Earth, the moon and Mars, and suggests that a huge collision could have brought all the precious metals to Earth at once.

The researchers believe that this happened before the Earth's crust formed – around 4.45 billion years ago.

Researchers from the Tokyo Institute of Technology led an international team of scientists in the study, in which a computer simulation tracked the evolution of the planets over their first 300 million years.

This is the longest that any team has ever tracked the evolution of the planets.

The results suggest that one large collision formed the precious metals, rather than a series of smaller meteorite impacts over a longer period of time, as was previously thought.

Earth has an unusually high proportion of precious metals near the surface, which is surprising, as they would usually be expected to settle down near the core of the planet.

Until now, this has been explained by the 'late veneer' theory, which suggests that foreign objects hit Earth, and in the process deposited the precious metals near the surface.

Speaking to the BBC about the late veneer theory, Matthias Willbold, a geologist at Imperial College London said: 'The theory is that after the core formed there was a meteoric shower that struck the Earth.

'These meteorites contained a certain amount of gold and that replenished the Earth's mantle and the continental crust with gold.'

But the results from the computer simulation challenge the late veneer theory.

Earth has an unusually high proportion of precious metals, such as gold, near the surface, which is surprising, as they would usually be expected to settle down near the core of the planet

The computer simulation took into account the metal concentrations on Earth, the moon and Mars, and suggests that a huge collision could have brought all the precious metals to Earth at once.

The researchers believe that this happened before the Earth's crust formed – around 4.45 billion years ago.

Their results also show that there was far less debris and material floating in the inner solar system than scientists had anticipated.

This suggests that the early Earth may have been a more benign place than previously thought.

The researchers hope that their findings will be incorporated into future simulations of the early solar system.

HOW THE MOON FORMED: THE GIANT IMPACT HYPOTHESIS

Many researchers believe the moon formed after Earth was hit by a planet the size of Mars billions of years ago.

This is called the giant impact hypothesis.

The hypothesis claims the moon is debris left over following an indirect collision between our planet and an astronomical body approximately 4.5 billion years ago.

The colliding body is sometimes called Theia, after the mythical Greek Titan who was the mother of Selene, the goddess of the Moon.

But one mystery has persisted, revealed by rocks the Apollo astronauts brought back from the moon - why are the moon and Earth so similar in their composition?

Several different theories have emerged over the years to explain the similar fingerprints of Earth and the moon.

Perhaps the impact created a huge cloud of debris that mixed thoroughly with the Earth and then later condensed to form the moon.

Or Theia could have, coincidentally, been isotopically similar to young Earth.

A third possibility is that the moon formed from Earthen materials, rather than from Theia, although this would have been a very unusual type of impact.