Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Earth’s Core is a Recycling Product

05.02.2004


The planets of the solar system, including the Earth, formed about four and a half billion years ago from a swirling disk of gas and dust that was left over from the newly formed Sun. However, we do not understand, why the Earth ended up being different from other Earth-like or «terrestrial» planets and how the earliest features, like the metallic core, developed. Research at ETH Zurich by Professor Alex Halliday, to be published in this week’s edition of Nature, claims to have found some answers.

It has generally been assumed that the Earth’s metallic core, which generates the magnetic field, formed by segregating dense metallic iron from the accumulated mixture of metal and silicate that was the primitive Earth. New modelling provides evidence that the core was most likely partly built by direct mixing of earlier formed planetary cores during extremely energetic collisions. Surprisingly, these proto-planets appear not to have had chemical compositions like the present Earth or even its closest neighbour the Moon. Instead, some of them were more like Mars. Indeed, Mars may be a very good analogue of what the Earth was like in its earliest stages of development.

«Embryoplanets» formed Earth



The Earth-like planets, including also Mercury, Venus and Mars, are thought to have been built up gradually, initially by sticking together of dust and rocky debris. When these objects reached the size of a kilometre or so gravity would have started to exert a major influence and a process called runaway growth would have consumed all of the debris in the vicinity. The bigger the planet the stronger its gravity and so the more it will attract other objects. However, this only builds objects that are about 1% of the mass of the Earth. Nearly all of the material in the inner solar system would then have been in the form of numerous roughly 1,000 km diameter planetary embryos. To get objects to be as big as the Earth requires that these embryos repeatedly collide by chance and gradually fuse into a much smaller number of discrete planets as we have today. These collisions would have been incredibly energetic and would have melted the colliding objects and even vaporized some of the rock and metal. It is thought that the Earth’s Moon formed from the debris produced in such a collision.

Date of Earth formation is hard to predict

Because this collision process is somewhat random it is also hard to predict. However, the various models that have been proposed differ with respect to the amount of time over which it is expected that the Earth would have taken to form. Some theories have predicted that the Earth would have formed in much less than one million years. Other, more widely accepted theories predict that it took ten to a hundred million years. Still other schools of thought have proposed something between these extremes. Extinct radioactive isotopes have proved particularly powerful in defining just how quickly planet formation occurred - allowing these theories to be tested. The isotopes of tungsten and lead are especially useful because they have been affected by the decay of radioactive hafnium and uranium respectively. The biggest change in hafnium to tungsten and uranium to lead ratio takes place during the core formation that accompanies planetary growth. This allows the isotopic compositions of tungsten and lead to be used to determine a rate of planetary growth. The data indicate that the Earth formed over tens of millions of years and that the Moon formed late, consistent with the theories of more protracted formation.

Earth’s Core formed from Earlier Planets

However, Halliday shows that the story is not so simple. The two isotopic clocks used, hafnium-tungsten and uranium-lead, actually give distinctly different timescales for planet formation when calculated in the same manner. Halliday shows that there is only one likely explanation for this. Some portion of the Earth’s core formed as a result of the coagulation of earlier cores from the colliding planets. This is different from the general view of core formation - that the iron metal from each colliding planet first mixed with the rocky outer parts of the Earth and then simply settled to the centre of the Earth because of its higher density. Furthermore, it means that the time-scales of formation of the Earth and Moon have been under estimated. Recently it was estimated that the Moon-forming Giant Impact took place at about 30 million years after the start of the solar system. An age for the Moon of closer to 50 million years now appears more likely.

Earth and Mars are relatives

The isotopic compositions of tungsten and other elements in the Moon can be used to deduce what the chemical composition of its impacting parent planet was like. It turns out it was probably much more like Mars – a relatively volatile-rich and oxidized planet. The Earth and the proto-planets that made the Earth most probably lost volatiles during growth. Given this history a big question that remains is how Earth acquired its water. This is, in fact, one of the most puzzling remaining problems about Earth-like planets.

Alex Halliday | alfa
Further information:
http://www.erdw.ethz.ch

More articles from Earth Sciences:

nachricht An Atom Trap for Water Dating
28.02.2017 | Universität Heidelberg

nachricht NASA eyes Pineapple Express soaking California
24.02.2017 | NASA/Goddard Space Flight Center

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Safe glide at total engine failure with ELA-inside

On January 15, 2009, Chesley B. Sullenberger was celebrated world-wide: after the two engines had failed due to bird strike, he and his flight crew succeeded after a glide flight with an Airbus A320 in ditching on the Hudson River. All 155 people on board were saved.

On January 15, 2009, Chesley B. Sullenberger was celebrated world-wide: after the two engines had failed due to bird strike, he and his flight crew succeeded...

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

Cells adapt ultra-rapidly to zero gravity

28.02.2017 | Health and Medicine

An Atom Trap for Water Dating

28.02.2017 | Earth Sciences

New pop-up strategy inspired by cuts, not folds

27.02.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>