The last moments of ancient water as it evaporated from a meteorite hurtling through space are identified in Nature Communications this week. These findings add weight to the suggestion that Earth’s water arrived from space.

Meteorites are chunks of bigger asteroids that have been floating around in space since the formation of the Solar System, 4.6 billion years ago. They are made from the first cosmic grains and may contain crucial information for determining the origins of both water and life on Earth. Yuki Kimura and colleagues investigated the magnetic properties of minute crystals in a meteorite that fell to Earth in Canada in the year 2000 to reveal the signature of ancient water that once existed in space. The team show that the magnetism of the tiny magnetite particles is such that the crystals could only have formed as the very last droplets of water dried out, leaving behind a unique watermark to be discovered billions of years later.