Scientists Find Evidence That Rain First Fell on Earth 4 Billion Years Ago

In elementary school, children learn about the water cycle. From evaporation to condensation into clouds to precipitation as rain, water cycles between land and sky. But when did this process begin? Earth itself is 4.5 billion years old, but freshwater was not immediately present. However, a new paper published in Nature Geoscience suggests Earth experienced its first rain earlier than previously thought. In fact, by examining the isotopes within some of Earth's oldest minerals, the researchers believe the hydrological cycle began 4 billion years ago.

The researchers examined Hadean zircon crystals from the Jack Hills in Australia. This remote dry region boasts these crystals, the oldest terrestrial bits of our planet. Zircons are minerals, inside which lurk isotopes that the team examined through secondary-ion mass spectrometry. They discovered traces of contact with water four billion years ago.

“We were able to date the origins of the hydrological cycle, which is the continuous process through which water moves around Earth and is crucial for sustaining ecosystems and supporting life on our planet,” shares lead author Dr. Hamed Gamaleldien. “By examining the age and oxygen isotopes in tiny crystals of the mineral zircon, we found unusually light isotopic signatures as far back as four billion years ago.

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