Earliest Signs of Fresh Water Unveiled by Ancient Crystals, Researchers Find
Ancient zircon crystals provide evidence of interaction with fresh water 4 billion years ago, hinting at a time when the Earth was believed to be engulfed in a global ocean. Chemical indicators within the crystals point to a unique connection with freshwater sources in the distant past.
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A recent study analyzing ancient grains of crystal found in rocks from the Australian outback reveals that Earth had dry land and fresh water around 4 billion years ago. This discovery challenges the previous belief that the planet was entirely covered by oceans during that time.
Chemical clues found in the crystals indicate that the hot, molten rocks they formed in came into contact with fresh water. This discovery was reported in a study published in the journal Nature Geoscience on Monday.
Lead study author Hamed Gamaleldien, who is an adjunct research fellow at Curtin University in Australia and an assistant professor at Khalifa University in the United Arab Emirates, explained that by analyzing the age and oxygen isotopes in tiny crystals of the mineral zircon, they discovered unusually light isotopic signatures dating back as far as four billion years. These light oxygen isotopes are typically produced when hot, fresh water alters rocks deep below the Earth's surface.
Gamaleldien explained that the presence of fresh water could only be possible if there was dry land for the water to collect and seep into the continental crust.
He emphasized, "We have two significant findings. We have found the oldest evidence of fresh water and indications of dry land above the sea."
The research shows that the Earth's water cycle, which involves the movement of water between land, oceans, and the atmosphere through evaporation and precipitation, was active during that time.
According to the authors, this discovery suggests that the conditions for the emergence of life existed less than 600 million years after the formation of Earth, predating the existence of dinosaurs and even the earliest known microbial life. The earliest widely accepted evidence of life, along with freshwater, can be traced back to stromatolites - fossilized microbes that formed mounds in hot springs 3.5 billion years ago, as noted by Gamaleldien.
Study coauthor Hugo Olierook, a senior research fellow at Curtin’s School of Earth and Planetary Sciences, highlighted that this discovery not only provides insights into Earth’s early history but also indicates that the presence of landmasses and fresh water allowed life to thrive in a relatively short period - less than 600 million years after the planet was formed.
Olierook added that these findings represent a major advancement in our knowledge of Earth's early history and offer new opportunities for investigating the origins of life.
Grains of zircon contain oxygen isotopes that reveal information about the environment they were formed in.
Grains of zircon contain oxygen isotopes that reveal information about the environment they were formed in.
Hamed Gamaleldien
A portal into early Earth
The Hadean Eon, occurring from 4.5 billion to 4 billion years ago, marks the beginning of Earth's history. It is a geological dark age that remains largely mysterious to scientists due to the lack of rocks dating back to that time period. The oldest rocks known to geologists are only 4 billion years old.
Zircon crystals play a crucial role in providing insights into the planet's early history. These tiny mineral grains are extremely durable and can become embedded in younger rock formations. In a recent study, zircons were discovered in 3.1 billion year-old orange sandstone from the Jack Hills formation in Western Australia.
Zircons are valuable to geologists because they contain uranium that helps determine their age through radioactive decay. The oldest terrestrial material discovered was a zircon from the Jack Hills formation, dating back 4.4 billion years.
Artist's rendition of the Ediacaran and our hypothesis
Artist's rendition of the Ediacaran and our hypothesis
Michael Osadciw/University of Rochester
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Zircon is a special mineral that is incredibly durable and remains unchanged over time. According to Gamaleldien, it is the only mineral that can provide insight into the Hadean period.
In order to make their discoveries, the researchers carefully extracted, prepared, and examined 2,500 zircon grains, which are as thin as two or three strands of human hair. They then dated 1,400 of these grains and analyzed the various oxygen isotopes present in the zircons.
Salt water is known to contain heavier oxygen isotopes that are resistant to evaporation, while rainwater typically contains lighter isotopes, according to Gamaleldien. In their study, two zircon crystals displayed isotopic evidence of meteoric or fresh water. One of these crystals was estimated to be around 4 billion years old, while the other was approximately 3.4 billion years old.
To further investigate, the team conducted 10,000 simulations of zircon composition using a computer model. This model explored scenarios where hot molten rocks interacted with seawater, rainwater, or a combination of both. Through their simulations, the researchers discovered that only when fresh water was introduced could they account for the light isotopic signature found in the zircons.
According to Gamaleldien, it is difficult to determine if there were large landmasses during the origin of life. However, there would have been some dry land above sea level. Additionally, the presence of land and fresh water, which may have come in the form of rain, would have supplied the necessary components for life to begin.
Scientists have different theories about life’s origins on Earth. Some believe it formed around deep ocean vents, but others suspect it came about in shallow bodies of water on land. Gamaleldien said the new findings provide support for the latter hypothesis, and the researchers want to recover more zircons for geochemical analysis to investigate further.
John Valley, a professor of geoscience at the University of Wisconsin-Madison, agreed that the conditions for life could have existed on Earth so long ago. Valley wasn’t involved in the new research but was among the first scientists to use zircons to show that Earth had ancient oceans and cooler temperatures more than 4 billion years ago, challenging the view that Hadean Earth was a hellish orb with fiery seas of magma.
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Valley mentioned that the fluid the zircon precursor interacted with might have been rainwater or seawater. The computer model used in the study assumed that the isotopic composition of the Hadean ocean was the same as today's oceans.
Valley added that the new paper's main finding was that the presence of rainwater suggests the rocks were on land rather than underwater. While this idea has been considered before, there is no new evidence provided to confirm this.
Geochemist Beth Ann Bell, an assistant researcher at UCLA’s department of earth, planetary and space sciences, pointed out that the very light isotope values suggest interactions between rock and fresh water during the Hadean period. This indicates the presence of some dry land at that time. She was not part of the study.
According to Bell, zircon is incredibly durable and does not erode easily on Earth’s surface. It can withstand billions of years in the crust and at the surface while retaining its valuable geochemical information.
Editor's P/S:
The discovery of ancient grains of crystal in rocks from the Australian outback has provided groundbreaking insights into Earth's early history. These crystals reveal the presence of dry land and fresh water around 4 billion years ago, challenging the previous belief that the planet was entirely covered by oceans during that time. This finding suggests that the conditions for the emergence of life existed less than 600 million years after the formation of Earth, predating the existence of dinosaurs and even the earliest known microbial life.
The presence of fresh water and dry land during this period is significant because it provides a suitable environment for the development of life. Scientists have long debated the origins of life on Earth, with some theories suggesting it formed around deep ocean vents and others proposing shallow bodies of water on land. The new discovery supports the latter hypothesis, indicating that life could have emerged in shallow lakes or ponds on land. Further research is needed to explore this possibility, but the findings presented in this article provide a promising foundation for future investigations into the origins of life on our planet.
