Ancient rocks reveal Earth had life-supporting conditions 4 billion years ago

Study of ancient zircon crystals reveals early interaction of water and land, challenging existing theories of a water-covered Earth

Earth may have had the necessary conditions to support life much earlier than previously thought. Analyses of ancient rocks and minerals to determine the composition of Earth’s early environment revealed that the planet most likely had the conditions for life only about 600 million years after its birth.

While Earth is estimated to be around 4.5 billion years old, the study indicates the presence of fresh water and dry land — the two crucial ingredients for life — as far back as 4 billion years ago, noted a new paper published in journal Nature Geoscience

The widespread interaction of fresh water and land on the early Earth may have created conditions conducive to the emergence of life. These interactions are referred to as the “water cycle”.

However, it is unclear when the water cycle began, which describes how water evaporates from the surface, rises into the atmosphere, cools, and condenses into rain or snow in clouds.

According to fossil evidence, the interaction between fresh water and the emerging continental crust began approximately 3.5 billion years ago. 

The researchers wondered if the water cycle began even earlier, more than 4 billion years ago.

So they looked into the origins of the Earth’s water cycle by studying oxygen isotopes (variants), which are especially sensitive to fluid-rock interactions. They investigated how two isotopes with atomic masses of 16 (light) and 18 (heavy) differed in dated rocks.

The researchers focused on zircon crystals found in the Jack Hills in Western Australia’s Midwest. These crystals, which are resistant to weathering and change, can be up to 4.4 billion years old, allowing the team to gain insight into early Earth.

“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,” Hamed Gamaleldien, adjunct research fellow in Curtin’s School of Earth and Planetary Sciences and an assistant professor at Khalifa University, United Arab Emirates, said in a statement

Such light oxygen isotopes indicate that water and rocks interacted with each other several kilometres below the Earth’s surface, he added.

“Fresh water and emerged land go hand in hand. If all land is underwater, then you can only have salty, ocean water. This is because salty water wants to encroach under land, a phenomenon known as seawater intrusion,” the authors of the paper wrote in nonprofit news source The Conversation.

This new evidence challenges the existing theory that Earth was completely covered by ocean four billion years ago. 

According to the researchers, these findings indicate that the conditions for life to flourish began relatively early, less than 600 million years after the planet formed. However, finding evidence of life during that period remains a challenge, the paper stated.

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