The Isotopic History of Earth’s Atmosphere Recorded in Lunar Hematite?

Credit: NASA GSFC Scientific Visualization Studio.

The surface of the Moon is a highly reduced environment, and lunar rocks and soils show that the Moon does not produce the iron-oxide mineral, hematite, through volcanic processes. Instead, many lunar lavas have a highly reduced form of iron present as metallic grains. On Earth and Mars, atmospheric oxygen and the oxygen in liquid water can turn iron in rocks and minerals a distinct rusty red color over time, also producing secondary and oxidized minerals like hematite. Recent work led by Shuai Li at the University of Hawaii presents spectral evidence for the presence of hematite on the Moon as well. Using data from the Moon Mineralogy Mapper, an imaging spectrometer that flew on Chandrayaan-1, Li and colleagues performed a global survey for hematite’s spectral signature and found that it is associated predominantly with east- and equator-facing sides of topographic highs on the Moon. The analysis also points to hematite being more concentrated on the lunar nearside than farside. The authors suggest a model for hematite formation through weathering processes that include oxygen delivered from the Earth, trace amounts of water in the lunar soil, and ongoing interplanetary dust impacts. The observed difference between the nearside and farside hematite concentrations might be explained by oxygen from Earth’s atmosphere delivered to the Moon’s nearside when the Moon passes through the Earth’s magnetotail. Creating a relatively oxidizing environment on the surface can potentially lead to hematite formation. If so, then it is possible that lunar hematite contains a prolonged record of oxygen isotopes from Earth’s atmosphere spanning billions of years. In this way, any lunar hematite brought back to the Earth by astronauts or robotic explorers could lead to an improved understanding of Earth’s atmospheric evolution through geologic time. READ MORE