- Analysis of lunar rocks brought back by the Apollo missions find telltale sign of the impact billions of years ago
- Scientists claim discovery could end the mystery of how moon formed
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Researchers claim to have found fresh physical evidence the Moon was created when a body the size of Mars smashed into the early Earth in a cataclysmic collision.
Analysis of lunar rocks brought back by the Apollo missions shows they have heavier forms of zinc - a telltale sign of the impact billions of years ago.
Without the Moon there may have been no life on Earth because it once orbited much closer to us than it does now causing massive tides to ebb and flow every few hours.
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Researcher say new analysis of lunar rocks prove the Moon was created when a body the size of Mars smashed into the early Earth in a cataclysmic collision.
These tides caused dramatic fluctuations in salinity around coastlines which are believed to have driven the evolution of primitive DNA-like biomolecules.
Planetary scientist Dr Frederic Moynier says the zinc enrichment probably arose because heavier atoms condensed out of the cloud of vaporized rock quicker than lighter onces.
His researchers analysed 20 samples of Moon rocks including ones from the Apollo 11, 12, 15 and 17 missions - all of which went to different locations - and one lunar meteorite.
Dr Moynier, of Washington University in St Louis, said: 'What we wanted were the basalts because they’re the ones that came from inside the Moon and would be more representative of the Moon’s composition.'
THE GIANT IMPACT THEORY
According to the Giant Impact Theory, proposed in its modern form at a conference in 1975, Earth's moon was created in a apocalyptic collision between a planetary body called Theia (in Greek mythology the mother of the moon Selene) and the early Earth.
This collision was so powerful it is hard for mere mortals to imagine, but the asteroid that killed the dinosaurs is thought to have been the size of Manhattan, whereas Theia is thought to have been the size of the planet Mars.
The smashup released so much energy it melted and vaporized Theia and much of the proto-Earth's mantle.
The Moon then condensed out of the cloud of rock vapor, some of which also re-accreted to the Earth.
Scientists have been looking for this kind of sorting by mass - called isotopic fractionation - since the Apollo missions first brought Moon rocks to Earth in the 1970s.
Compared to terrestrial or Martian rocks the lunar rocks have much lower concentrations of zinc but are enriched in the heavy isotopes of zinc.
'The magnitude of the fractionation we measured in lunar rocks is 10 times larger than what we see in terrestrial and Martian rocks,' Moynier says, 'so it's an important difference.'
Earth and Mars have isotopic compositions like those of chondritic meteorites, which are thought to represent the original composition of the cloud of gas and dust from which the solar system formed.
The most likely large-scale event is wholesale melting during the formation of the Moon.
The zinc isotopic data therefore supports the theory a giant impact gave rise to the Earth-Moon system.
Dr Moynier, whose study is published in Nature, said: 'The work also has implications for the origin of the Earth because the origin of the Moon was a big part of the origin of the Earth.'
Without the stabilising influence of the Moon the Earth would probably be a very different sort of place.
Scientists think the Earth would spin more rapidly, days would be shorter, weather more violent and climate more chaotic and extreme.
In fact it might have been such a harsh world it would have been unfit for the evolution of humans.
Asked how he felt when he saw the first results, Moynier says, 'When you find something that is new and that has important ramifications, you want to be sure you haven't gotten anything wrong.
'I half expected results like those previously obtained for moderately volatile elements, so when we got something so different, we reproduced everything from scratch to make sure there were no mistakes because some of the procedures in the lab could conceivably fractionate the isotopes.'
The data, published in the Oct. 18, 2012, issue of Nature, provide the first physical evidence for wholesale vaporization event since the discovery of volatile depletion in Moon rocks, Moynier says.
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