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A new NASA study of Apollo lunar soil reveals that meteorites could not have been the dominant source of Earth’s water.
Researchers analyzed the Moon’s regolith, which serves as a preserved record of the solar system’s impact history. By using triple oxygen isotopes—as distinct “fingerprints” unaffected by impact heat—they identified how much water could have been delivered by meteorites after 4 billion years ago.
The study found that the volume of water supplied during this period would be a tiny fraction of Earth’s current oceans. While meteorites contributed some water, the data suggests late-stage bombardment alone cannot account for Earth’s vast water reserves, favoring theories involving earlier delivery or Earth’s native geological processes.
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