People have life, old age, illness and death, the length of life, but a hundred years. For everything in the world, the vast universe, as small as microscopic particles, cannot escape the iron law of continuous aging. The Earth has a history of 4.56 billion years since its birth.
Water, as the source of life, is also experiencing the cycle of life. Do you know how old the oldest water is?
The origin of water
Where does the water on Earth come from? Opinions vary on this issue.
Some people believe that water is a substance that existed when the earth was formed, which is "autologous theory". Some scholars regard water as an "alien visitor", believing that water is brought by the solar wind and comets, which is "exogenous theory".[1]
When does water appear? There is also controversy. However, in an analysis of meteorites about 4.5 billion years ago, scientists have found traces of water, suggesting that water may have been present at the beginning of the Earth's origins.[1]
Figure 1: The ocean covers 71% of the Earth's surface, making the Earth a veritable "water balloon" and making it a vibrant planet. (Image from Wikipedia)
So, when did the oldest water we find today come from?
Age of groundwater
The water on the surface of the earth is rushing endlessly, or used by passive plants, or evaporated into the heavens, or into the sea, experiencing the water cycle on the surface, and constantly experiencing "rebirth". In contrast, water entering the ground circulates much more slowly and has a longer life cycle. Therefore, when the age of water is mentioned, it mainly refers to the age of groundwater.
In general, groundwater will go through three processes: replenishment, runoff, and discharge, that is, water seeps into the ground from the surface, flows underground, and returns from the ground to the surface. The duration of this cycle can range from a few days to millions of years. The time that groundwater stays underground is called the age of groundwater.
How is the age of groundwater determined? The most commonly used is isotopic techniques. It selects specific radioactive elements in groundwater according to the characteristics of the constant decay rate of radioactive elements, and measures the radioactive element content before and after decay respectively to calculate the age of groundwater. Different elements have different decay cycles and therefore different age ranges that can be measured.
Figure 2: Commonly used groundwater dating isotopes and their dating ranges[2]
Where is groundwater?
Where is groundwater distributed? Where is the groundwater and is it likely to be the oldest?
Groundwater is mainly distributed in pores, fissures, or caverns in underground rock. Different rocks and soils have different abilities for water to pass through. This ability to allow water to move in the geotechnical body is called the permeability of the geotechnical body. The more permeable the rock mass, the easier it is for water to pass through it. In general, the speed of water in the rock and soil is very wide, the slow one is measured in millimeters every year, and the fast one can even travel thousands of meters a day.
Therefore, for most groundwaters, even if the movement speed is slow, after millions of years, it tends to disappear. This has created difficulties in the search for ancient groundwater.
(a) Pore water (b) Fissured water (c) Karst water
▲Figure 3: Schematic diagram of pore water, fissured water, karst water
If you want to find the oldest groundwater, you have to go to places with low permeability and water that is not easy to escape. There are two main places like this:
01
Fluid inclusions
When mineral crystals of rocks are formed, a part of the liquid and gas are trapped in tiny bubbles in the crystals and become fluid inclusions. These inclusions are generally small in size, ranging from 0.01 mm to 1 mm, and there is often very little liquid in them. The liquid here is generally older.
Figure 4: Fluid inclusions in mineral crystals (Image from Wikipedia)
02
Closed rock mass fissures
If the fractures in the rock mass are closed due to tectonic movement, sedimentation and other reasons after the water enters, and the rock mass around the fractures is particularly dense, the fissure water "trapped" in it may be preserved for a long time. Such fissure water, which is much larger than a fluid inclusion, is an excellent choice for finding ancient groundwater.
Figure 5: Groundwater in tight, closed rock mass fissures can often be preserved for a long time
The oldest groundwater
In 2013, scientists found water stored in cracks in copper-zinc deposits at a depth of 2.4 km at the Kidd Creek Mine near Timmins, Ontario, Canada. The deposits are nearly 2.7 billion years old, and the water is perfectly sealed in the fractures of the deposits. Drill through rock crevices and flow water up to two liters per minute.[3][4] The amount of water is astonishing.
Figure 6: Where kidd Creek Mine is located
Figure 7: Exterior view of Kidd Creek Pit
The scientists carefully collected water samples and measured the contents of the inert gas isotopes helium, neon, argon and xenon contained in the water, and concluded that the age of water was at least more than 1 billion years. Combined with a comprehensive analysis of other elements in the water, the age of these waters may be around 1.5 billion years[3][4].
Figure 8: Ancient groundwater flowing from the cracks in the rock mass of the mine[3]
Figures 9 and 10: Scientists collect water samples from a mine
Figure 11: The results were published in Nature in 2013
In 2016, deeper (2.9 km) deeper into the Kidd Creek mine, scientists collected new water samples and, after analysis, found that the average age of these waters was around 1.6 billion years old, and the oldest could even reach 2 billion years, setting a new record for the oldest water.
Thus, the oldest known groundwater is over 1.6 billion years old[5][6].
It should be noted that due to the age, there is a certain error in the identification results. Different identification methods produce different results. Therefore, scientists can only determine a rough range compared to the exact age value. It is believed that with the continuous advancement of scientific exploration, the continuous improvement of technical means, and the continuous development of dating methods, we will find more and more ancient groundwater in the future, and the determination of its age will be more accurate.
Some readers may wonder: how does such an ancient groundwater taste like? The answer may disappoint everyone. Due to the long-term underground storage, the physicochemical reaction occurs between the water and the rock, and a large number of substances are dissolved in the water, resulting in a high mineral content in the water, which is a veritable "mineral water". If you taste it, the taste must be bitter and astringent.
Figure 12: Eight glasses of water a day, health is always with you. How much water did you drink today?
Water and the Origin of Life
The search for the oldest water on Earth is also a search for the secret of the origin of life. Life first originated in water. Water as a necessary solvent for life, in which many important elements and compounds are dissolved, such as hydrogen, methane, nitrogen, carbon dioxide and ammonia, etc., water mixes and interacts with these substances to produce organic matter. The organics aggregated into more complex combinations and began to grow and reproduce, and the earliest life was born. Therefore, exploring the substances contained in the oldest water is an important clue to the origin of life.
Figure 13: The origin and evolution of life, all of which are inseparable from water. (Image courtesy of NASA)
In ancient groundwater collected at the Kidd Creek mine, researchers found it rich in methane and hydrogen, essential to support life activities. In addition, sulfates produced by chemical reactions with rocks have been found in the water. This shows that closed groundwater bodies have physicochemical conditions that support life activities. In the sequestered groundwater, there may also be a colorful world of life.[3][4]
This discovery makes the deep groundwater body a potential habitable area for life, greatly expanding the range of life activities and providing new clues for the discovery of life on Earth and extraterrestrials.[5] There are many unsolved mysteries about the oldest water, and its relationship to life, waiting to be explored further...
bibliography:
1、 FANG Linru. Where does water come from[J].Earth, 2020(08):30-33.
2、 Clark I . Groundwater geochemistry and isotopes. 2015.
3、 Jessica Marshall. Reservoir deep under Ontario holds billion-year-old water[J]. Nature News ,2013
4、 G. Holland, et al, Deep fracture fluids isolated in the crust since the Precambrian era[J]. Nature 497, 357–360, 2013
5、 Sherwood Lollar, et al, Exploring the deep, ancient hydrogeosphere within Precambrian crystalline rocks using noble gases[J], AGU Fall Meeting, 2016
6、 https://www.sciencealert.com/the-world-s-oldest-water-lies-deep-below-canada-and-it-s-2-billion-years-old
Editor: Wan Peng
Editor: Jiang Qingqing
Proofreader: Wang Haibo