Earth as seen by the Apollo 11 astronauts floating above the moon
NASA
A mysterious layer of space dust that coated Earth millions of years ago could be shrapnel from asteroids that smashed into the moon, according to a new analysis of soil from below the sea floor.
In the 1990s, geologists found unusually raised levels of helium-3 across Earth’s crust, dating back to around 33 million years ago. This was puzzling because the isotope almost always appears only in objects from space, as a result of bombardment by cosmic rays. …