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How freshwater, which sustains life, came to be on Earth has continued to be a source of mystery, with experts believing so far that it was the result of water-carrying asteroids and comets pummeling Earth more than four billion years ago.

Now, geologists from Khalifa University in Abu Dhabi, along with other Australian researchers, have determined that rock crystals from some of the world’s oldest rocks in Australia indicate that freshwater had already appeared on Earth around that time.

According to the findings, published in the journal Nature Geoscience earlier this week, freshwater appeared on Earth almost 600 million years before what the existing theories and data suggest. The findings date the presence of water on Earth to four billion years ago, a mere 600 million years after the planet formed.

Also learn about evaporation in rocks:

Rocks on Earth contain minerals and salts, which can be studied for their concentrations in the lab. The researchers analyzed isotopes of oxygen molecules to understand whether salty water might have evaporated from rocks to rain back down.

When water evaporates from the surface of the ocean or tops of rocks, it leaves behind salt, while simultaneously undergoing molecular makeup changes. The lighter isotope of oxygen called oxygen-16 evaporates quicker than oxygen-18. This oxygen-16-rich water returns in the form of rain, and once again undergoes evaporation, where more oxygen-18 remains behind. Over a period, freshwater becomes concentrated in oxygen-16, while seawater mainly comprises the heavier oxygen-18.

Meanwhile, oxygen-16 water also percolates into rocks when it rains down and reacts chemically with rocks or magma deep underground. This releases oxygen-16 molecules in these structures, providing evidence of freshwater permeation.

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