Deep mantle clues to Earth's watery beginning.

Earth's ocean makes the planet habitable by regulating the climate and sustaining the water and nutrient cycles that support life. This life-essential body of water is believed to have formed early, nearly 4.4 billion years ago. The mantle crystallized from a magma ocean, a mass of molten rock with dissolved water that covered the planet during its formation. The crystallization expelled most of the water to the surface, but a small fraction was held in the solidified mantle. The mineral bridgmanite is key for understanding early water distribution. On page 1177 of this issue, Lu et al. (1) report an increase in the partitioning of water into bridgmanite with increasing temperature, suggesting that the amount of water dissolved into the rock was more substantial when the hot magma ocean crystallized than previously thought (2). This finding is important for understanding the initial water distribution on early Earth. [ABSTRACT FROM AUTHOR]