While most of the minerals in Moon rocks are found on Earth, they were formed in very different environments. Moon rock shows evidence of formation in an extremely dry setting, with low gravitational influence and very little surrounding oxygen.
This is completely opposed to the Earth’s environment at the time of formation, approximately between three and four and a half billion years ago. Lunar rocks also contain trapped gases from the solar wind passing them at the time of formation.
The solar wind is a continuous stream of charged, highly energetic particles originating at the Sun and moving out in all directions. The gases found in lunar samples match the isotope ratios expected for gas from this source, and are significantly different to isotope ratios found on Earth.
Overall there are many differences between Moon rock and Earth rock; some were expected but others were great discoveries made by investigating the samples brought back from the Apollo missions.
Answered by Megan Whewell of the National Space Centre