The Moon’s Big Impact | Chemical & Engineering News
Volume 92 Issue 23 | p. 28 | Concentrates
Issue Date: June 9, 2014

The Moon’s Big Impact

Oxygen isotope ratios support the idea that the moon formed from the collision of a planet-sized body with Earth
Department: Science & Technology
News Channels: Analytical SCENE
Keywords: giant impact hypothesis, moon, oxygen isotope ratios

For the first time, scientists have found physical evidence that supports the reigning hypothesis of how Earth’s moon was formed (Science 2014, DOI: 10.1126/science.1251117). A Mars-sized body, which scientists call Theia, is believed to have slammed into early Earth billions of years ago. In the aftermath, fragments, mostly of Theia, coalesced into the modern-day moon. However, no differences between moon and Earth rock samples had been found to show evidence that Theia came calling. A standard marker for such differences is the 17O/16O ratio, which has a characteristic value in most of our solar system’s bodies. Daniel Herwartz of Georg August University, in Göttingen, Germany, and colleagues took a closer look at freshly prepared lunar samples, using the latest in isotope ratio mass spectrometry techniques. They found that the 17O/16O ratio of lunar samples was shifted 12 ppm from the ratio in Earth samples. That difference is enough to validate the giant impact hypothesis, the researchers say. “The next goal is to find out how much material of Theia is in the moon,” Herwartz says.

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Lunar rock samples, compared with meteorites such as the one shown here, provide evidence for the giant impact formation hypothesis.
Credit: Courtesy of Addi Bischoff/U of Münster
A section of a meteorite.
 
Lunar rock samples, compared with meteorites such as the one shown here, provide evidence for the giant impact formation hypothesis.
Credit: Courtesy of Addi Bischoff/U of Münster
 
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