Earth Lost 40 Percent Mass During Formation

The violent and chaotic process that led to the formation of Earth resulted in the loss of more than 40 percent of its mass, says a study. Analysing a mixture of earth samples and meteorites, the scientists shed new light on the sequence of events that led to the creation of our home planet. Planets grow by a process of accretion - a gradual accumulation of additional material - in which they collisionally combine with their neighbours. This is often a chaotic process and material gets lost as well as gain, said the study published in the journal Nature.

Massive planetary bodies impacting at several kilometres per second can generate substantial heat which, in turn, produces magma oceans and temporary atmospheres of vaporised rock. Repeated loss of this vapour envelope during continued collisional growth causes the planet's composition to change substantially. "We have provided evidence that such a sequence of events occurred in the formation of the Earth and Mars, using high precision measurements of their magnesium isotope compositions," said lead researcher Remco Hin from the University of Bristol in Britain.

"Magnesium isotope ratios change as a result of silicate vapour loss, which preferentially contains the lighter isotopes. In this way, we estimated that more than 40 percent of the Earth's mass was lost during its construction," he said. For the study, the researchers analysed samples of the Earth together with meteorites from Mars and the asteroid Vesta, using a new technique to get higher quality measurements of magnesium isotope ratios than previously obtained.

"We now show that vapour loss during the high-energy collisions of planetary accretion has a profound effect on a planet's composition," Hin said. "This process seems common to planet building in general, not just for Earth and Mars, but for all planets in our Solar System and probably beyond, but differences in the collision histories of planets will create a diversity in their compositions," he added.

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