Earth’s first primitive form was created in just five million years — up to seven times faster than had been previously thought, researchers have found.
In fact, if the whole of the solar system’s history was condensed into a 24-hour-period, the Earth’s formation would have taken the equivalent of 90 seconds.
In contrast, experts had previously thought that this process would have taken 16.7–50 million years, — or, in the 24-hour-clock analogy, equivalent to around 5–15 minutes.
The Danish team eschew traditional theories that the proto-Earth formed through random collisions of larger and larger planetary bodies over tens of millions of years.
Instead, they put forward the idea the planets formed through the relatively rapid build-up of cosmic dust.
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Earth’s primitive form was created in five million years — much faster than had been previously thought, researchers have found. Pictured, an artist’s impression of a protoplanetary disk
‘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 paper author Martin Schiller, of the University of Copenhagen.
‘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 key to the new findings came through the most precise to date measurements of the mixture of iron isotopes in different meteorites.
Dr Schiller and colleagues found only one type of meteoritic material with a composition similar to that of the Earth — a type known as ‘CI chondrites’.
Dust in this type of meteorite is described by the team as the best equivalent to the bulk composition of the solar system itself — and it was dust like this, along with gas, that formed the disc of matter around the Sun from which the planets formed.
When the young Earth first began to form, the iron dust helping to build it up had a unique composition, like thanks to thermal alteration from the Sun.
After the solar system’s first few hundred thousands of years, it became cold enough for unaltered CI dust from further out in the system to enter the region where the the proto-Earth was being built up.
‘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,’ Dr Schiller explained.
‘That is why the core formation must have happened early.’
‘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.’
The Danish team eschew traditional theories that the proto-Earth formed through random collisions of larger and larger planetary bodies over tens of millions of years. Instead, they put forward the idea the planets formed through the relatively rapid build-up of cosmic dust. Pictured, an artist’s impression of the young Earth, as viewed from space
‘If the theory of early planetary accretion really is correct, water is likely just a by-product of the formation of a planet like the Earth,’ said paper co-author and Copenhagen University cosmochemist, Martin Bizzarro.
This, he added, makes the ingredients of life as we know it more likely to be found elsewhere in the universe.
‘When we understand these mechanisms in our own solar system, we might make similar inferences about other planetary systems in the galaxy — including at which point, and how often, water is accreted.’
Researchers believe that other planets in the universe may also rapidly through the accretion of cosmic dust.
This means that planets outside of our own solar system may from faster than had been though, potentially increasing the likelihood of finding life elsewhere in the universe.
The full findings of the study were published in the journal Science Advances.
HOW DO PLANETS FORM?
According to our current understanding, a star and its planets form out of a collapsing cloud of dust and gas within a larger cloud called a nebula.
As gravity pulls material in the collapsing cloud closer together, the centre of the cloud gets more and more compressed and, in turn, gets hotter.
This dense, hot core becomes the kernel of a new star.
Meanwhile, inherent motions within the collapsing cloud cause it to churn.
As the cloud gets exceedingly compressed, much of the cloud begins rotating in the same direction.
The rotating cloud eventually flattens into a disk that gets thinner as it spins, kind of like a spinning clump of dough flattening into the shape of a pizza.
These ‘circumstellar’ or ‘protoplanetary’ disks, as astronomers call them, are the birthplaces of planets.