Moon and Earth have common water source

Water rights: Earth and Moon share a source

About 4.5 billion years ago when a giant collision sent a disc of debris from Earth to form the Moon, some of Earth’s water traveled along. Geochemist Alberto Saal and colleagues used isotopic composition as a fingerprint to trace the history. Credit: Mike Cohea/Brown University

Researchers used a multicollector ion microprobe to study hydrogen-deuterium ratios in lunar rock and on Earth. Their conclusion: The Moon’s water did not come from comets but was already present on Earth 4.5 billion years ago, when a giant collision sent material from Earth to form the Moon.