Oldest Evidence of Earth's Atmosphere May Reside in Lunar Rocks

The moon, which hasn’t had a magnetic field for 4.36 billion years, might hold ancient Earth's atmospheric fragments. A new study analyzing moon rocks brought back by Apollo astronauts 50 years ago suggests that these rocks could contain the oldest traces of Earth's atmosphere.

Initially, scientists detected magnetism in these moon rocks, indicating the moon once had a magnetic field similar to Earth’s. However, magnetic fields are driven by a celestial body's core, and the moon's core is relatively small. This was perplexing, noted John Tarduno, an Earth and environmental sciences professor at the University of Rochester. Recent studies, however, indicate the moon’s magnetic field lasted only for its first 140 million years.

The study, published in the journal Communications Earth & Environment, suggests that in the absence of a protective magnetic field, the moon could have captured ions from Earth's atmosphere 4.36 billion years ago. Tarduno pointed out the difficulty in measuring Earth's early atmosphere due to heavy alterations by tectonic activity. By contrast, the moon's geologically quiet surfaces, particularly undisturbed layers of lunar soil, might offer direct evidence of what our planet's early atmosphere looked like.

Magnetic fields arise from the motion of magnetic materials within a celestial body's core, shielding it from solar winds. Iron-bearing rocks, when cooled and solidified, align magnetic minerals according to the existing magnetic field, locking this orientation in place. It’s particularly noteworthy that single crystals within these rocks act as robust records of geomagnetic fields.

In 2021, Tarduno’s team found that the moon hadn't had a magnetic field for 3.9 billion years. In their new study, which pushed the date back by 400 million years, the team closely examined older lunar samples, revealing none showed specific magnetic orientation.

Delving into Earth's first eon, the Hadean, through lunar records is noteworthy because no Hadean rocks remain on Earth. Furthermore, evidence from the study deepens the mystery of Earth’s atmospheric conditions under a dim sun. Early greenhouse gases could have created a warming haze, making the planet habitable despite lower solar luminosity.

Tarduno emphasized the significance of understanding planetary evolution and habitability, stating, "If we can't understand Earth, how can we say anything about the evolution of other planets?"

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