Some 4.6 billion years ago, Earth was nothing like the gentle blue planet we know today. Frequent and violent celestial impacts churned its surface and interior into a seething ocean of magma—an environment so extreme that liquid water could not exist, leaving the entire planet resembling an inferno.

Since 70% of Earth’s surface is now covered in oceans, the mystery of how water survived and preserved on our planet from an early molten to a mostly solid state has long been a subject of scientific study.