Earth's makeup found to be more diverse than previously thought

Mar 02, 2012 by Bob Yirka report
Earth

(PhysOrg.com) -- For most of modern science, researchers have believed that the Earth was primarily made up of enstatite chondrites, a subclass of meteorites. This was because of the similarity of chromium, nickel and oxygen isotope proportions found on Earth as they compared to enstatite chondrites. Now however, new research by a pair of French geochemists studying silicon isotopes found on Earth, the moon and several types of meteorites, suggest, as they describe in their paper published in Science, that the ingredients that make up the Earth are likely more diverse.

Most researchers believe that the formation of the began as left over from the formation of the sun clumped together due to gravity. After that, the Earth accreted as it was struck by meteorites, which up until now, were believed to be mostly enstatite chondrites. After billions of years of new material being added, the Earth eventually grew to its present size. This new research suggests that more types of meteorites were involved in that process than has generally been thought.

The two geochemists, Bernard Bourdon and Caroline Fitoussi had a hunch that there was likely more to the story, so they began collecting samples from a variety of rocks focusing specifically on silicon . They then applied the same kind of attention to samples of rocks brought back from the moon. Next, they compared their findings with two kinds of meteorites that have been found on the Earth’s surface: Enstatite chondrites and enstatite achondrites. They followed all that up by feeding all of their information into a computer model that simulated the formation of the Earth and found that a mixture of at least three types of meteorites could have led to the amounts of chromium, and oxygen isotopes we find today but could also explain the amounts of silicon isotopes found in all the rocks they studied.

Because of this, they say, it appears likely that the Earth accreted from more kinds of meteorites than has been suggested by previous studies, which means its composition is likely more varied than has generally been thought.

In addition, as part of their study, they noted that silicon isotope measurements between Earth and moon samples were so similar that it appears likely that the moon was made from the same material as the Earth’s mantle, which gives credence to the theory that the moon was once a part of the Earth but was torn away by a very large asteroid strike at some later date.

Explore further: NASA satellites measure increase of Sun's energy absorbed in the Arctic

More information: Silicon Isotope Evidence Against an Enstatite Chondrite Earth, Science DOI: 10.1126/science.1219509

ABSTRACT
The compositions of Earth materials are strikingly similar to those of enstatite chondrite meteorites in many isotope systems. Although this suggests that Earth largely accreted from enstatite chondrites, definitive proof of this model has been lacking. By comparing the Si isotope signatures of several extraterrestrial materials with terrestrial samples, we show that they cannot be explained by core formation scenarios involving a bulk Earth of enstatite chondrite composition. Si isotope similarities between the bulk silicate Earth and the Moon preclude the existence of a hidden reservoir in the lower mantle, a necessary condition of the enstatite chondrite model, and require an equilibrium process after the Moon-forming impact. A three-endmember chondritic mixing model for the Earth reconciles the Si isotope similarities between enstatite chondrites and Earth.

Related Stories

Missing chromium is clue to planet formation

Feb 24, 2011

Early in the formation of the Earth, some forms of the element chromium separated and disappeared deep into the planet's core, a new study by UC Davis geologists shows.

Atomic Particles Help Solve Planetary Puzzle

Nov 10, 2009

(PhysOrg.com) -- A University of Arkansas professor and his colleagues have shown that the Earth's mantle contains the same isotopic signatures from magnesium as meteorites do, suggesting that the planet formed ...

Meteorites: Tool kits for creating life on Earth

Aug 08, 2011

Meteorites hold a record of the chemicals that existed in the early Solar System and that may have been a crucial source of the organic compounds that gave rise to life on Earth. Since the 1960s, scientists have been trying ...

Half-baked asteroids have Earth-like crust

Jan 07, 2009

Asteroids are hunks of rock that orbit in the outer reaches of space, and scientists have generally assumed that their small size limited the types of rock that could form in their crusts. But two newly discovered ...

Lutetia: A rare survivor from the birth of the Earth

Nov 11, 2011

(PhysOrg.com) -- New observations indicate that the asteroid Lutetia is a leftover fragment of the same original material that formed the Earth, Venus and Mercury. Astronomers have combined data from ESA’s ...

Recommended for you

Improving forecasts for rain-on-snow flooding

6 hours ago

Many of the worst West Coast winter floods pack a double punch. Heavy rains and melting snow wash down the mountains together to breach riverbanks, wash out roads and flood buildings.

The Greenland Ice Sheet: Now in HD

6 hours ago

The Greenland Ice Sheet is ready for its close-up. The highest-resolution satellite images ever taken of that region are making their debut. And while each individual pixel represents only one moment in time, ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

julianpenrod
1 / 5 (1) Mar 04, 2012
Yet another case of "science" announcing a discovery completely invalidating earlier disocveries claimed to be "definitive". And a dicsovery that apparently didn't necessarily need the additional research to be traditionally arrived at. If the earth's silicon isotopes could be explained by considering different types of meteorite compositions than earlier studies used, it would have been seen earlier that the standard meteorite types were insufficient, so it could have been concluded that the earth was assembled from several different types of meteorites. That is assuming that it's not the case that any theory of asteroid accretion could explain earth's make-up and they were only waiting until several additional types of meteorites were examined to claim that they matched earth's composition.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.