Earth's water may have originally been formed by chemical reactions deep within our planet's mantle, according to new research.
The new theory offers an alternative explanation as to how the life-giving liquid may have originated on Earth.
Previously, scientists have suggested that comets that collided with the planet could have deposited large amounts of ice on the Earth which later melted, forming water.
Researchers led by University College Dublin (UCD) in Ireland carried out computer simulations which found that reactions between high-pressure and high-temperature fluid hydrogen and silicon dioxide in quartz, found in Earth's upper mantle, can form liquid water under the right conditions.
The exercise tested the reaction at different temperatures and pressures typically found in the upper mantle 40 to 400km below the surface of the Earth.
The simulations revealed that the silica and fluid hydrogen could form water when exposed to temperatures of just over 1400 degrees Celsius and at pressure 20,000 times higher than Earth's atmospheric pressure.
Silica is found in abundance above and below the surface of the Earth in the form of the mineral quartz the Earth's crust is 59 per cent silica.
The scientists had expected that the water would form on the surface of the silica, but instead, they were surprised to find that the water remained trapped inside the silica, leading to a massive build up of pressure.
They also believe the release of this pressure could be responsible for triggering earthquakes hundreds of kilometres below the Earth's surface.
The new findings support the experiments on the same reaction between silicon dioxide and liquid hydrogen carried out by Japanese scientists in 2014.
"We were initially surprised to see in-rock reactions, but we then realised that we had explained the puzzling mechanism at the base of earlier Japanese experimental work finding water formation," said Professor Niall English from UCD School of Chemical and Bioprocess Engineering.
"We concluded that these findings help to rationalise, in vivid detail, the in-mantle genesis of water. This is very exciting and in accord with very recent findings of an 'ocean's worth' of water in the Earth's mantle," English added.
The findings were published in the journal Earth and Planetary Science Letters.