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Physical Chemistry

Nuked zinc isotopes on Earth support moon formation theory

Trinity nuclear test site provides a ready-made laboratory for the study of evaporative isotope fractionation

by Elizabeth K. Wilson
February 13, 2017 | A version of this story appeared in Volume 95, Issue 7

A hand holding a trinitite sample
Credit: Scripps Institution of Oceanography/UC San Diego
This trinitite sample contains fractionated zinc isotopes and hints about how the moon formed.

A study of glass formed by sand that was fused during the first nuclear bomb test not only demonstrates that high temperatures fractionate zinc isotopes, but also strengthens the giant-impact theory of the moon’s formation (Sci. Adv. 2017, DOI: 10.1126/sciadv.1602668). The moon is highly depleted in volatile elements such as zinc compared with Earth. Scientists have suggested that the volatiles likely evaporated when a planet-sized object hit the nascent Earth billions of years ago, and the moon formed from the detritus. But in lunar samples, the zinc isotope fractionation patterns—the distribution of isotope abundances relative to each other—have been difficult to interpret in the context of the giant-impact scenario. A group led by James Day of Scripps Institution of Oceanography turned to the site of the 1945 Trinity nuclear bomb test in New Mexico, which is a rare ready-made laboratory. The tremendous heat and pressures created by the nuclear blast were similar to those believed to be involved in planetary formation and can’t otherwise be simulated on Earth. The explosion melted silica on the desert floor, producing a green glass called trinitite. The researchers found that the closer the trinitite samples were to the original blast site, the more fractionated the zinc isotopes, supporting the moon-formation hypothesis.


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