Fresh examinations of lunar rocks gathered by Apollo mission astronauts have yielded proof of a huge impact that may have shaped and given birth to the moon
Researchers at the Washington University headed by Frederic Moynier say tehy have discovered evidence that the Moon was born in a flaming blaze of glory when a body the size of Mars collided with the early Earth.
The evidence might not seem all that impressive to a nonscientist: a tiny excess of a heavier variant of the element zinc in Moon rocks. But the enrichment probably arose because heavier zinc atoms condensed out of the cloud of vaporised rock created by a catastrophic collision faster than lighter zinc atoms, and the remaining vapor escaped before it could condense.
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, and Moynier together with Randal Paniello, and colleague James Day of the Scripps Institution of Oceanography are the first to find it.
The Moon rocks, geochemists discovered, while otherwise chemically similar to Earth rocks, were woefully short on volatiles (easily evaporated elements). A giant impact explained this depletion, whereas alternative theories for the Moon's origin did not.
But a creation event that allowed volatiles to slip away should also have produced isotopic fractionation. Scitentists looked for this but were unable to find it, leaving the impact theory of origin in limbo for more than 30years.
The data, published in the journal Nature, provide the first physical evidence for the vaporisation event since the discovery of volatile depletion in Moon rocks, Moynier says.
According to the Giant Impact Theory, Earth's moon was created in a apocalyptic collision between a body called Theia 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 vaporised Theia and much of the Earth's mantle. The Moon then condensed out of the cloud of rock vapor, some of which also re-accreted to the Earth. Compared to terrestrial or martian rocks, the lunar rocks the team analysed have much lower concentrations of zinc but are enriched in the heavy isotopes of zinc.
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 simplest explanation for these differences is that conditions during or after the formation of the Moon led to more extensive volatile loss and isotopic fraction than was experienced by Earth or Mars.
The isotopic homogeneity of the lunar materials, in turn, suggests that isotopic fractionation resulted from a large-scale process rather than one that operated only locally. Given these lines of evidence, the most likely large-scale event is wholesale melting during the formation of the Moon. The zinc isotopic data therefore supports the theory that a gaint impact gave rise to the earth-Moon system.
Without the stabilizing influence of the Moon, the Earth would probably be a very different sort of place. Planetary sciences 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 our favourite species:us.
Researchers at the Washington University headed by Frederic Moynier say tehy have discovered evidence that the Moon was born in a flaming blaze of glory when a body the size of Mars collided with the early Earth.
The evidence might not seem all that impressive to a nonscientist: a tiny excess of a heavier variant of the element zinc in Moon rocks. But the enrichment probably arose because heavier zinc atoms condensed out of the cloud of vaporised rock created by a catastrophic collision faster than lighter zinc atoms, and the remaining vapor escaped before it could condense.
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, and Moynier together with Randal Paniello, and colleague James Day of the Scripps Institution of Oceanography are the first to find it.
The Moon rocks, geochemists discovered, while otherwise chemically similar to Earth rocks, were woefully short on volatiles (easily evaporated elements). A giant impact explained this depletion, whereas alternative theories for the Moon's origin did not.
But a creation event that allowed volatiles to slip away should also have produced isotopic fractionation. Scitentists looked for this but were unable to find it, leaving the impact theory of origin in limbo for more than 30years.
The data, published in the journal Nature, provide the first physical evidence for the vaporisation event since the discovery of volatile depletion in Moon rocks, Moynier says.
According to the Giant Impact Theory, Earth's moon was created in a apocalyptic collision between a body called Theia 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 vaporised Theia and much of the Earth's mantle. The Moon then condensed out of the cloud of rock vapor, some of which also re-accreted to the Earth. Compared to terrestrial or martian rocks, the lunar rocks the team analysed have much lower concentrations of zinc but are enriched in the heavy isotopes of zinc.
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 simplest explanation for these differences is that conditions during or after the formation of the Moon led to more extensive volatile loss and isotopic fraction than was experienced by Earth or Mars.
The isotopic homogeneity of the lunar materials, in turn, suggests that isotopic fractionation resulted from a large-scale process rather than one that operated only locally. Given these lines of evidence, the most likely large-scale event is wholesale melting during the formation of the Moon. The zinc isotopic data therefore supports the theory that a gaint impact gave rise to the earth-Moon system.
Without the stabilizing influence of the Moon, the Earth would probably be a very different sort of place. Planetary sciences 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 our favourite species:us.
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