ANU scientists produce the best estimate to date of Earth’s composition

There are still some lingering questions about what exactly our home planet is made up of.

IT MIGHT come as a surprise to you but there’s actually a lot we don’t know about the Earth’s composition.

If so, you’re in good company because it was also somewhat of a surprise to Dr Charles Lineweaver, a planetary scientist at Australian National University.

“We too were surprised that we didn’t know this better than we did,” he told

Our deepest drilling has only scratched the surface so scientists use magnetic fields and seismic waves to measure the density and movement of the various materials deep below our feet.

We know, for example, that the core is mostly iron. We also know that more than 90 per cent of the planet’s mass is made up of iron, oxygen, silicon and magnesium. But the finer details about the internal makeup of Earth are by no means a given.

Dr Lineweaver and two other researchers from the Canberra-based university, Haiyang Wang and Professor Trevor Ireland, believe they have come up with “a new and improved elemental composition of Earth”.

The motivation for the project was to better understand the composition of planets both within and outside our solar system, to know which ones could be habitable.

“Basically we’re astrophysicists. We’re starting to find exoplanets all over the universe and we know that they’re rocky and wet and many of them are going to be very Earth-like and we want to know more about these things.”

Astronomers have been estimating the composition of stars in the galaxy for about a hundred years, Dr Lineweaver said.

“We said; wait a minute, if we know the composition of the star, that probably tells you a lot about the composition of the rocky planets that we strongly believe are in orbit around almost every star.”

To test this theory they looked at the composition of the Sun and the Earth to better understand the process that took place 4.6 billion years ago when a dense blob in a molecular cloud of hydrogen gas and dust collapsed under its own gravity to form the early Sun, Earth and other planets.

Ultimately, they set about “making the best comparison ever of the Sun and the Earth”.

To do so they looked at all the data and literature on the elemental composition of the Earth and Sun, with all the uncertainties included.

“We looked at all the literature on the composition of the Earth and said: ‘Holy cow, these people, they’re not doing the whole Earth, they’re just doing the mantle. And holy cow, these people they’re just looking at the core.”

There wasn’t a complete picture with all the uncertainties of the data included to help them in their quest.

“We were very disappointed and said we’re going to have to do this ourselves,” he said.

That was about a year ago and their efforts have now been published in the international journal Icarus, in what Dr Lineweaver described as “a new and improved elemental composition of Earth”.

The new model produced by the research suggests Earth contains significantly more sodium, potassium, chlorine, zinc, strontium, fluorine, gallium, rubidium, niobium, gadolinium, tantalum, helium, argon, and krypton than previously believed.

It also points to the fact that the abundances of magnesium, tin, bromine, boron, cadmium, and beryllium within our planet seem to be significantly lower than previously thought.

This NASA image shows our home planet in April 2016.


Co-researcher Prof Trevor Ireland from the ANU Research School of Earth Sciences said planetary scientists would find many uses for this new composition record.

“This will have far-reaching importance, not only for planetary bodies in our Solar System but also other star systems in the universe,” he said.

For Dr Lineweaver, the next step is to use the type of analysis employed in the writing of the paper to investigate the composition of the planets around Alpha Centauri, the closest star system to our own.

Alpha Centauri is about 4.37 light-years away and is thought to host some potentially Earth-like planets.

The big question, said Dr Lineweaver, is: “How will they be different from Earth and what does that mean for their habitability?”

And he has a particular species in mind who might be very interested in such knowledge.

“In about 100, or 1000 or maybe 10,000 years there’s a species of technological apes that seems to be ruining their home planet,” he said, only half jokingly.

“One (way) to prevent the extinction of these technological apes is to find habitable planets elsewhere, particularly around Alpha Centauri which is the closest other star.”

An artist’s impression of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System.



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Cherry May Timbol – Independent Reporter
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The reason it is called “Law” is because it has been “proven”!

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