The Earth formed much more quickly than we thought, study says

The Earth formed much more quickly than we thought, according to a new study.

And it did so in a newly theorised way, with pieces of dust gradually sticking together to form the pro-Earth that became our planet, the research suggests.

The formation of that proto-Earth took 5 million years, according to the study from the Centre for Star and Planet Formation (StarPlan) at the Globe Institute at the University of Copenhagen.

That is so quick that if the solar system's 4.6 billion years of existence were thought of as a day, the Earth only formed in about a minute-and-a-half.

The speed was the result of the way that the Earth formed, the scientists say.

The traditional story of the formation of the Earth suggests that it was formed as big planetary bodies collided with each other, gradually building up into the planet that would become our Earth over a relatively long period of a few tens of millions of years.

But the new study suggests our planet is the result of a much faster process of growth as tiny objects assembled to create what would become our Earth.

"The other idea is that we start from dust, essentially. Millimetre-sized objects, all coming together, raining down on the growing body and making the planet in one go," said associate professor Martin Schiller.

"Not only is this implication of the rapid formation of the Earth interesting for our solar system. It is also interesting to assess how likely it is for planets to form somewhere else in the galaxy."

The new study was made possible after scientists examined iron isotopes found on Earth, and comparing them across different meteorites. They found that there is only one type of material that looks similar to that on Earth, known as "CI chrondrites".

The dust in those meteorites is the best equivalent we have to our own solar system. A similar dust would have once been found in a disc around our growing Sun, in its earlier life, over a process of about five million years.

It was in that disc that the planets in the solar system were created. Researchers suggest that the particular make-up of Earth means that it must have already been made during this period, suggesting that it happened early enough that process had already happened.

'This added CI dust overprinted the iron composition in the Earth's mantle, which is only possible if most of the previous iron was already removed into the core. That is why the core formation must have happened early,' said professor Schiller.

'If the Earth's formation was a random process where you just smashed bodies together, you would never be able to compare the iron composition of the Earth to only one type of meteorite. You would get a mixture of everything."