Study sheds new light on how Earth and Mars were created

September 27, 2017
Snapshot of a computer simulation of two (relatively small) planets colliding with each other. The colours show how the rock of the impacting body (dark grey, in centre of impact area) accretes to the target body (rock; light grey), while some of the rock in the impact area is molten (yellow to white) or vaporized (red). Credit: Philip J. Carter

Analysing a mixture of earth samples and meteorites, scientists from the University of Bristol have shed new light on the sequence of events that led to the creation of the planets Earth and Mars.

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 gained.

Massive planetary bodies impacting at several kilometres per second generate substantial heat which, in turn, produces magma oceans and temporary atmospheres of vaporised rock.

Before planets get to approximately the size of Mars, gravitational attraction is too weak to hold onto this inclement silicate atmosphere.

Repeated loss of this vapour envelope during continued collisional growth causes the planet's composition to change substantially.

Dr Remco Hin from the University of Bristol's School of Earth Sciences, led the research which is published today in Nature.

He said: "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.

"Magnesium isotope ratios change as a result of silicate vapour loss, which preferentially contains the lighter . In this way, we estimated that more than 40 per cent of the Earth's mass was lost during its construction.

"This cowboy building job, as one of my co-authors described it, was also responsible for creating the Earth's unique composition."

The research was carried out in an effort to resolve a decades long debate in Earth and planetary sciences about the origin of distinctive, volatile poor compositions of planets.

Did this result from processes that acted in the mixture of gas and dust in the nebula of the earliest solar system or is it consequence of their violent growth?

Researchers analysed samples of the Earth together with meteorites from Mars and the asteroid Vesta, using a new technique to get higher quality (more accurate and more precise) measurements of magnesium isotope ratios than previously obtained.

The main findings are three-fold:

  • Earth, Mars and asteroid Vesta have distinct magnesium isotope ratios from any plausible nebula starting materials
  • The isotopically heavy magnesium isotope compositions of planets identify substantial (~40 per cent) mass loss following repeated episodes of vaporisation during their accretion
  • This slipshod construction process results in other chemical changes during growth that generate the unique chemical characteristics of Earth.

Dr Hin added: "Our work changes our views on how planets attain their physical and chemical characteristics.

"While it was previously known that building planets is a violent process and that the compositions of planets such as Earth are distinct, it was not clear that these features were linked.

"We now show that vapour loss during the high energy collisions of planetary accretion has a profound effect on a planet's .

"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 will create a diversity in their compositions."

Explore further: Why are there different 'flavors' of iron around the Solar System?

More information: 'Magnesium isotope evidence that accretional vapour loss shapes planetary compositions' by R. Hin, C. Coath, P. Carter, F. Nimmo et al in Nature. dx.doi.org/10.1038/nature23899

Related Nature paper: dx.doi.org/10.1038/nature23645

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Chris_Reeve
1 / 5 (2) Sep 27, 2017
If so, then what of this?

https://www.space...ula.html

"Earth and the other rocky planets aren't made out of the solar system's original starting material, two new studies reveal.

Scientists examined solar particles snagged in space by NASA's Genesis probe, whose return capsule crash-landed on Earth in 2004. These salvaged samples show that the sun's basic building blocks differ significantly from those of Earth, the moon and other denizens of the inner solar system, researchers said ...

McKeegan and his team measured the abundance of solar wind oxygen isotopes. Isotopes are versions of an element that have different numbers of neutrons in their atomic nuclei. Oxygen has three stable isotopes: oxygen-16 (eight neutrons), oxygen-17 (nine neutrons) and oxygen-18 (ten neutrons).

The researchers found that the sun has significantly more oxygen-16, relative to the other two isotopes, than Earth."
ddaye
5 / 5 (1) Sep 27, 2017
"This slipshod construction process" Evidently study also disputes Intelligent Design.
Graeme
not rated yet Sep 28, 2017
What happened to all that evaporated magnesium? Once the vapour cooled down it would have formed interplanetary dust, which may or may not have fallen back down to a planet, or been blown far from the sun by the solar wind. If 40% was blown away, then it may have formed planets in the outer solar system by now.
rrwillsj
1 / 5 (2) Sep 28, 2017
Oh ddaye, you misunderstood the temporary conclusions of this study. Rather it is further proof of "Intelligent Design".

Now follow this randomly bouncing ball... The deity is only thirteen+ billion years old. Still a baby! Do you really think it's a coincidence that the gases composing the stars are the same as the gases composing flatulence?

After all, our lives are determined by events outside our control. That Life itself is just a crapshoot.

The Galaxies are butt diapers for the infant creator. The Universe, a trillion years from now when the deity matures, will be unrecognizable to us sooner microbes.

The concept of "Intelligent Design" is proof for the Truism "That the smartest people commit the stupidest mistakes!"

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