Scientists reveal the hiding place of all the water on Earth 4.6 billion years ago

Once upon a time, Earth was a hot planet with magma flowing in one vast ocean. When our home was born 4.6 billion years ago, space was not the kindest place. The chaotic environment and the constant bombardment caused the planet’s surface and interior to remain in a near-constant molten state. So if magma was spread everywhere, where was water? According to a study, Earth was hiding it all deep within a mineral in the mantle. This was a time when the flowing magma turned the planet into a blazing furnace. Over millions of years, Earth transitioned from being a hot piece of cosmic body in a molten state to a cool and calm solid planet. The oceans were filled with water, which was hiding somewhere on the planet.

Professor Zhixue Du from the Guangzhou Institute of Geochemistry of the Chinese Academy of Sciences (GIGCAS) tried to decode this mystery of the hiding place of Earth's water. According to the researchers on his team, large quantities of water were effectively "locked away" deep inside Earth’s mantle. A mineral found abundantly in the mantle acted like a microscopic "water container" as the planet solidified. Their findings have been published in Science.

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Simulation revealed something new about the water-absorbing mineral

This water reservoir is what helped Earth transform from a fiery planet into the habitable world we know today. The team set out to test a previous theory, according to which bridgmanite had limited water storage capacity in low-temperature conditions. They built a diamond anvil cell experimental setup equipped with laser heating and high-temperature imaging to understand the extreme conditions at depths exceeding 660 kilometres, and detect water signals in bridgmanite samples. They gradually raised temperatures to approximately 4,100 degrees Celsius, which helped them learn how it affects the ability of minerals to pull in water.

This simulation revealed that bridgmanite’s “water-locking” capacity increased with rising temperature. This means that during Earth’s hottest “magma ocean” phase, it had changed to retain a lot more water. After the magma ocean solidified, the lower mantle became the largest water reservoir in the solid mantle. Gradually, this water reached the surface through magmatic activity.