A new analysis of ancient grains of crystal embedded in rock from the Australian outback suggests Earth had dry land and fresh water some 4 billion years ago — a time when scientists had thought the planet was completely covered in ocean.
Chemical clues contained in the crystals revealed that the hot, molten rocks in which they originated came into contact with fresh water during the crystals’ formation, according to a study published Monday the journal Nature Geoscience.
“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,” said lead study author Hamed Gamaleldien, an adjunct research fellow in Curtin University’s School of Earth and Planetary Sciences in Australia and an assistant professor at Khalifa University in the United Arab Emirates, in a news release. “Such light oxygen isotopes are typically the result of hot, fresh water altering rocks several kilometres below Earth’s surface.”
Gamaleldien said that evidence of the presence of fresh water could only be explained by the existence of dry land — where water would collect and seep into the continental crust.
“We have two important things here. We have discovered the earliest evidence of fresh water and representative evidence for dry land above the sea,” he added.
The research indicates that the Earth’s water cycle — when water moves between land, oceans and atmosphere through evaporation and precipitation — was operating at that point in time.
This finding, the authors said, means the recipe for the origins of life existed less than 600 million years after Earth’s formation, long before the dinosaurs or even the earliest known microbial life. The earliest widely agreed upon evidence of life — and fresh water — comes from stromatolites, fossilized microbes that formed mounds in hot springs 3.5 billion years ago, Gamaleldien said.
“This discovery not only sheds light on Earth’s early history but also suggests … landmasses and fresh water set the stage for life to flourish within a relatively short time frame — less than 600 million years after the planet formed,” said study coauthor Hugo Olierook, a senior research fellow at Curtin’s School of Earth and Planetary Sciences, in a statement.
“The findings mark a significant step forward in our understanding of Earth’s early history and open doors for further exploration into the origins of life,” he added.
