Isotope Ratios Clarify Moon’s Origin | Chemical & Engineering News
Volume 94 Issue 5 | p. 29 | Concentrates
Issue Date: February 1, 2016

Isotope Ratios Clarify Moon’s Origin

Space Science: Analysis of oxygen isotopes points to a mixing of water and rocky melt between nascent Earth and the planetary body Theia when they collided to form our satellite
Department: Science & Technology
News Channels: Analytical SCENE
Keywords: moon, Earth, oxygen, isotopes
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Samples such as this one, collected from the moon during the Apollo 17 mission, help resolve the origin of Earth’s satellite. Image taken under cross-polarized light conditions.
Credit: Paul Warren, UCLA
Close up of a moon rock under cross-polarized light conditions.
 
Samples such as this one, collected from the moon during the Apollo 17 mission, help resolve the origin of Earth’s satellite. Image taken under cross-polarized light conditions.
Credit: Paul Warren, UCLA

The making of our moon, according to a widely accepted theory, took place billions of years ago when a giant planetary body called Theia collided with a nascent Earth, producing debris that eventually became our planet’s satellite. Although scientists think the crash certainly occurred, they still debate the details: For example, is the moon primarily made of debris from Theia or from a mix of the two planetary bodies? One way to resolve these and other debates is to compare isotope ratios of moon and Earth rock samples. At the time of the collision, Theia and Earth would have had different isotope ratios, a characteristic of all planets. So if today’s moon and Earth samples have different isotopic ratios, then the moon likely originated from Theia’s debris only. A new study in Science finds the opposite—at least according to oxygen isotope ratios. A team of researchers led by Edward D. Young and Issaku E. Kohl of UCLA report that Earth and the moon have “indistinguishable oxygen isotope ratios” (2016, DOI: 10.1126/science.aad0525). The scientists propose that during the collision, there was substantial mixing of water and rock between both planetary bodies, leading to common, averaged oxygen isotope ratios on Earth and the moon-forming debris.

 
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