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 Colorado River's connection with the ocean was a punctuated affair
16.11.2017 | University of Oregon

nachricht Researchers create largest, longest multiphysics earthquake simulation to date
14.11.2017 | Gauss Centre for Supercomputing

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

Im Focus: Wrinkles give heat a jolt in pillared graphene

Rice University researchers test 3-D carbon nanostructures' thermal transport abilities

Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

NASA detects solar flare pulses at Sun and Earth

17.11.2017 | Physics and Astronomy

NIST scientists discover how to switch liver cancer cell growth from 2-D to 3-D structures

17.11.2017 | Health and Medicine

The importance of biodiversity in forests could increase due to climate change

17.11.2017 | Studies and Analyses

VideoLinks
B2B-VideoLinks
More VideoLinks >>>