Hotter Mantle Caused Enormous “Water World” in Ancient Earth

An enormous ocean covered the Earth in the early Archean period up to four billion years ago- a result of the planet's hotter mantle during the epoch, research revealed.

The study disputes earlier beliefs that Earth's global ocean had a size that stayed constant over time while providing hints about its changing size throughout the geologic period.

Most of the surface water on Earth lies in the oceans. A second reservoir, however, is in the interior of the Earth, found in the form of hydrogen and oxygen stuck on minerals in the Earth's mantle. The new research approximates the amount of water the mantle could store at present and kept in the past.

Larger Ocean Might Have Existed in Archean Epoch

Results show that since Earth was hotter before, the mantle could have held less water because minerals at the mantle could contain less water at higher temperatures. If we assume that the mantle carries more than 0.3-0.8 times the ocean's mass, a larger ocean could have existed in the early Archean epoch. During that period, the mantle was around 1,900 to 3000 degrees Kelvin (2,980 to 4,940 degrees Fahrenheit), against the current mantle temperatures of 1,600-2,600 degrees Kelvin (2,420 to 4,220 degrees Fahrenheit).

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If the Earth had a vaster ocean at the time, it could have changed the atmosphere's composition, decreasing the amount of sunlight reflected back into space, the researchers said. These would have a direct effect on the climate and the habitat during the Earth's early years.

The Earth's interior, they say, impacts what goes on the surface. If the mantle could only hold so much water, they added, it's got to go to the surface.

(Photo: patrickltr on Unsplash) Studies reveal that an enormous ocean might have existed in ancient Earth due to a hotter mantle.

In the last 541 million years, Earth's sea level remained constant. However, the Earth's ocean levels at an earlier time would be difficult to estimate since little evidence remains from the Archean period. Water can travel from the surface to the interior using plate tectonics throughout geologic time, yet the size of that water flux is difficult to understand. Due to this lack of data, scientists believed that the size of the global ocean stayed constant over geologic time.

First-ever Study Linking Mantle Water Physics Data To Ocean Size

Scientists built a model to approximate the total amount of water the mantle could potentially hold based on temperature. Incorporating existing data on the amount of water various mantle minerals can keep and considered which among the 23 minerals would have occurred in varying depths and periods in the Earth's past. They would compare those estimates with the surface ocean's volume when the Earth cooled.

This is the first time scientists connected mineral physics data on mantle water storage to the size of the ocean.

Such estimates on the storage capacity of the mantle show a lot of uncertainty. This is illustrated by the fact that the amount of water in bridgmanite, the main mantle mineral, could not be determined.

These study results can shed light on the changes that happened in the global ocean over geologic time and help determine water cycles on Earth and other planets, which is valuable in understanding how life could have evolved.

Using the same approach, scientists are estimating how much water might have been stored inside Mars.