Moon and Earth have common water source

11 May ScienceDaily

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.

Water inside the Moon's mantle came from primitive meteorites, new research finds, the same source thought to have supplied most of the water on Earth.

The findings raise new questions about the process that formed the Moon.The Moon is thought to have formed from a disc of debris left when a giant object hit Earth 4.5 billion years ago, very early in Earth's history. Scientists have long assumed that the heat from an impact of that size would cause hydrogen and other volatile elements to boil off into space, meaning the Moon must have started off completely dry.