When did fresh water appear on Earth? Earlier than believed

A team of scientists from Curtin University (Australia) has found evidence that fresh water on Earth appeared about 4 billion years ago. 500 million years earlier than thought and very shortly after the planet itself was formed, in a simple blink of an eye in geological time.

When did the hydrological cycle begin?

The researchers analyzed oxygen molecules within zircon crystals dating back 4 billion years from Jack Hills in Western Australia, one of the oldest rock formations on Earth. Specifically, they used secondary ion mass spectrometry to analyze the small zircon grains and deduce which oxygen isotopes were present in the magma from which the crystals formed. (With the CAMECA 1300HR3 instrument at the Large Geometry Ion Microprobe (LGIM) facility at the John de Laeter Center with which they carried out more than 10,000 simulations of zircon composition using a computer model).

When using the oxygen isotopic composition From these ancient zircon crystals they discovered that the specific ratios of the heaviest and lightest isotopes of oxygen in the zircons indicate the presence of a significant amount of fresh water. Most zircons had relatively high oxygen isotope values, as would be expected from seawater. But in two periods of time, about 3.4 billion years ago and 4 billion years ago, the proportions indicated a higher proportion of lighter oxygen. Most of the zircons were much younger, with the most recent crystals dating back to 1.85 billion years ago. In 3.4 billion-year-old zircons, the team measured ratios of oxygen-18 to oxygen-16 that were as low as 0.1 per thousand.

They contain evidence of fresh water, which indicates that patches of land must have existed (and with it, the first continents), since fresh water can only form if there is land for it to accumulate after precipitation.

Fresh water, long before

“We were able to date the origins of the hydrological cycle, which is the continuous process through which water moves around the Earth and is crucial to sustaining ecosystems and sustaining life on our planet,” explained Hamed Gamaleldien, leader of the work published in the journal Nature Geoscience. “By examining the age and oxygen isotopes in small crystals of the mineral zircon, we found unusually light isotopic signatures dating back to 4 billion years ago.” (Salt water contains heavier oxygen isotopes, which are resistant to evaporation, while rainwater contains lighter isotopes.) “Evidence of fresh water at this depth in the Earth’s interior challenges the existing theory that the Earth was completely covered by an ocean 4 billion years ago“says the expert.

It is the earliest evidence of fresh water and land above the sea. This means that the recipe for the origins of life existed less than 600 million years after the formation of Earth, long before the earliest known microbial life. Without a doubt, this research has implications for many fields of science.

“This discovery not only sheds light on Earth’s early history, but also suggests that land masses and fresh water set the stage for life to flourish in a relatively short period of time: less than 600 million years.” after the planet formed,” says Hugo Olierook, from Curtin University and co-author of the study. “The findings mark an important step forward in our understanding of the early history of Earth and open doors for further exploration of the origins of life.”

Zircons are extraordinarily resistant. It is very strong and does not alter over time; That is why they are so extremely useful for understanding when the continental plates formed by the crust began to break the surface of the global ocean. The findings also suggest that at that time enough land had already arisen above sea level to support a water cycle. And, for the moment, they are one of the few reliable data sources What we tell about the early Earth is quite difficult to study.

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