According to foreign media reports, the origin of life on earth has been an unsolved mystery that has puzzled scientists for decades. At present, the latest research shows that early life on the earth may have started from “poisonous hot springs”. At the same time, we have a deep understanding of the formation process of complex molecules on the earth. , Will help guide us to find life forms on other planets in the solar system.
Picture from WiKiMedia
In the “Bumpass Hell” in Lassen Volcanic National Park, California, the ground is boiling, the air is filled with the smell of rotten eggs, and bubbles are gushing from the mud pits, releasing the popping sound of viscous liquid and hot steam. Erupting from the crater of the earth. This terrible terrain was named after the cowboy Kendall Bumpass. In 1865, when Bumpass approached here, he stepped on the thin crust and the boiling acid water severely burned his leg. Department, resulting in him having to undergo amputation.
The picture shows the “Bumpass Hell” in Lassen Volcanic National Park, California, USA. The wetting and drying cycle at the edge of the geothermal pool is believed to promote the accumulation of biomolecules.
Some scientists argue that life on Earth gradually formed under seemingly uninhabitable conditions. Before organisms wandered on the earth, hot springs like Bompass Hell might promote chemical reactions and connect simple molecules together. , Thus taking the first step towards complex life. However, other scientists have focused the starting point of life on Earth on hydrothermal vents deep in the seafloor, where mineral-rich hot water rolls out of seafloor cracks.
This latest research provides important theoretical support when researchers study and debate where life on Earth was born and how it exploded. Natalie Batalha, an astrophysicist at the University of California, Santa Cruz, said that understanding the origin of life on this planet may provide important clues to the search for extraterrestrial life.
Wenonah Vercoutere, a chemist at NASA’s Ames Research Center, agrees. She said: “This latest research is of great significance to the future of space exploration. The physical rules of the entire universe are It’s the same, so why can’t the laws of biology continue? Why is there no biological activity in the entire universe?”
Land hot spring
From the perspective of biochemistry, the composition of life depends on only a few elements: chemical elements, water, or other media that can undergo chemical reactions, and the energy source that powers these reactions. On the earth, all these ingredients exist in terrestrial hot springs, which are home to some tenacious creatures. For example: An article published in the Journal of Nature Communications in 2016 pointed out that in the “Great Boiling Spring” in Nevada, the hot spring temperature is as high as 77 degrees Celsius, but microorganisms still managed to survive in the waters near the hot spring clay beach .
Jennifer Pett-Ridge, a microbial ecologist at Lawrence Livermore National Laboratory in California, said: “The living environment like this may be very close to the early earth environment, so these life forms are most likely Related to some early life on Earth.”
Microorganisms in hot springs can form biological communities called “microbial mats”. Microbial mats are composed of multiple layers of microorganisms. They are found in geothermal areas all over the world, including: Yellowstone National Park in the United States, and Gal in southern Russia. Add hot springs, and the Lassen Volcanic National Park in California, the location of the “Bompass Hell”.
Over time, the microbial mat can form stromatolites, a layered structure of microorganisms and minerals accumulating. The layered structure of stromatolites reflects the geological changes over time, just like the annual rings of trees.
Researchers found evidence of stromatolites in 3.5 billion-year-old rocks in the outback of Western Australia, as well as related evidence of hot spring deposits. The relevant content was published in the 2017 issue of Nature Communications. This latest discovery and previous microbial-related signs led the research team to believe that some of the earliest life on earth thrived in such a hot spring environment.
David Deamer, a biophysicist at the University of California, Santa Cruz, spent 45 years exploring how life on Earth originated and evolved. He began to study lipids, the oily molecules that make up the membranes around cells.
Demer is a strong supporter of hot springs-the origin of life theory. He once proved that the earth hot springs can produce bubble-like vesicles whose outer layer is made of lipids. A structure like this may be the progenitor precursor of modern cells.
Scientists believe that the Bravo Hot Springs in Iceland is one of the environments where life may have formed on the early earth.
Bruce Damer, an astrobiologist at the University of California, Santa Cruz, used computer science methods to solve the problem of the origin of life. He collaborated with Demer to test whether the conditions of the hot springs can promote a condensation reaction, that is, two molecules combine to form a larger one. Composition.
When the water splashes from the hot spring and evaporates, the molecules in the liquid will condense and connect. The subsequent splashing will add more molecules. These molecules can undergo additional condensation reactions when the liquid evaporates again, repeatedly moisturizing. Moisture and evaporation can produce molecular chains.
In 2018, Daimer conducted an experiment in an active geothermal area in New Zealand. The experiment was named “Hell’s Gate”. To test this hypothesis, he prepared a vial containing the components needed to assemble the RNA strand. The RNA is A type of nucleic acid that acts as a messenger in the process of protein synthesis and may have catalyzed chemical reactions related to the origin of early life on Earth. This mixture includes two of the four RNA building components. These nucleotides are linked together to form RNA chain.
Daimer put the opened vial in a metal box, the metal box is the size of two CD boxes, and then put the device in a hot liquid pool close to boiling. In order to simulate the sometimes humid and sometimes dry environment of the primitive earth, he poured acidic hot spring water into the vial to gradually evaporate and dry the vial, and then repeated the wet-dry cycle several times. When he took the vial back to the laboratory, he found that it contained RNA-like strands of 100-200 nucleotides in length.
The results of this study were published in the December 2019 issue of the Astrobiology Journal. The study showed that complex molecules can be formed in hot springs, thus supporting the hypothesis that life on earth may survive and develop in such an environment. In 2020, Dammer and Demer and their colleagues returned to the “Hell’s Gate” experiment site again to confirm the results of Dammer’s research and conducted more wet-dry cycle studies.
Nicholas Hud, a chemist at the George Institute of Technology in Atlanta, USA, studies the origin of life from a slightly different perspective: he explored how DNA and RNA nucleotides originate, and he agrees that these molecules are more on land than in the ocean. It is more likely to be connected together by a condensation reaction, where wet and dry cycles can occur. These reactions will produce water. When there is a lot of water around the living environment, the formation of such chemical bonds is energetically unfavorable. Hood said: “The best place to form this structure is a hot and dry place. It is the least likely to form them in a humid and hot environment.”
However, there is evidence that the humid, high-temperature environment is where life originated. At the hydrothermal vents on the dark deep seabed, heated water gushes into the sea, and its temperature is only a few degrees Celsius above freezing.
In 2017, researchers found 3.77 billion-year-old fossil evidence in Quebec, Canada, which originated from the ancient seabed and showed various signs of hydrothermal activity. Researchers claim that these unique fossil structures are similar to microorganisms, indicating that there may be evidence of early life on Earth in the deep sea environment.
The chemical composition of vents such as limestone chimneys found in the “Lost City” of the Atlantic Ocean supports the survival of microorganisms.
These submarine environments can be extremely extreme: some heat wave vents that spew black water jets have temperatures as high as 400 degrees Celsius. However, if the hydrothermal vent plays an important role in nurturing early life, it is likely to be a hydrothermal vent with a suitable temperature. For example: “The Lost City” is a hydrothermal area in the middle of the Atlantic Ocean. The temperature of the fluid flowing from the crater is between 40-90 degrees Celsius. It is famous for its eye-catching limestone chimneys. Some submarine limestone chimneys are about 60 in height. Meter.
These limestone chimneys are the home of microbes. They feed on a chemical reaction product called serpentinization. Laurie Barge, an astrophysicist at NASA’s Jet Propulsion Laboratory in California, said: “Hydrothermal fluids Spouts are a very interesting environment because they are located at the interface of water and rock.”
In areas like the Lost City, the chemical reaction between water and rocks makes the water flowing from the vents more alkaline than the water in the ocean, which contains a higher concentration of positively charged hydrogen ions. The gradient change from alkaline water to acidic water is like the difference between the positive and negative electrodes of a battery, and it can be used as an energy source for chemical activity.
In order to study the condition of underwater hydrothermal vents, Bagh established a simulated environment in the experiment. She said: “We can simulate what we see in nature.” To depict the ocean environment of the early Earth, she set up an inverted glass bottle It is filled with an acidic mixture that contains iron but does not contain oxygen. One end of the plastic tube passes through the narrow bottom of the glass bottle and is connected to a stable alkaline solution, which acts like a vent.
The researchers simulated an alkaline hydrothermal vent in an acidic ocean to explore the chemical composition of the ancient ocean. Such conditions can produce a chimney structure.JPL-Caltech/NASA
When Bagh and colleagues injected an alkaline spout solution containing RNA nucleotides into a marine mock bottle, the individual RNA nucleotides would be joined into short chains. These short chains are only 3-4 nucleotides in length, but the researchers reported in a research report published in the journal “Space Biology” in 2015 that the conditions of deep-sea hydrothermal vents may support the related reactions of life on earth.
For Demer, there are huge obstacles to assembling life elements near underwater hydrothermal vents: the vast ocean dilutes molecules, so they will not be concentrated enough to trigger chemical reactions. In addition, there is no “dry-wet cycle” in the underwater environment. This requires repeated evaporation processes to gather enough molecules together to make them collide with each other to react and form longer chains. In addition, Demer said that unlike fresh water in hot springs, salty sea water inhibits the formation of thin films and inhibits the reaction of molecules linking together.
However, academic circles have also criticized Demer’s hot spring theory. Astrobiologist David Des Marais of NASA’s Ames Research Center said: “DNA and RNA chains are made up of It is composed of phosphate and sugar molecules alternately, but sugar is very unstable in a hot spring environment.”
It may be too early to rule out the “dry-wet cycle” under water. Bill Brazelton, a marine microbiologist at the University of Utah in Salt Lake City, USA, said: “There may be some water stored in the vent, and then Because the crater consumes water for serpentinization, which creates other molecules, you can perform these dehydration cycles in the rocks on the sea floor.”
Scientists may not be able to determine how life was born on the earth: most of the earliest geological records on the earth have disappeared. In addition to the hot springs and deep sea vents on the earth, there are many speculation theories about the origin of life. For example: The latest research shows that asteroid collisions may transport superheated seawater into the earth’s crust, creating a hydrothermal system similar to hot springs.
Desmaras said: “I think we must admit that in order to promote the breeding and reproduction of life, early life may have gone through many bumpy roads.”
Researchers are using the knowledge they have learned to analyze when and where life originated and developed on the earth. This knowledge may guide humans to find biological characteristics outside the earth. There are currently several promising planets in the solar system, and mysterious life forms are likely to occur on these planets.
Bataha, a scientist at the University of California, Santa Cruz, said: “NASA is really interested in whether there is life in the ocean below the surface of ice-covered satellites such as Europa and Enceladus.” Scientists have evidence that these two There is a salty liquid ocean beneath the ice crust on the surface of the satellite.
The picture shows the water vapor spewing from the frozen surface of Enceladus taken by NASA’s “Cassini” spacecraft, which contains compounds of carbon, nitrogen and oxygen. The hydrogen in the plume is evidence of hydrothermal activity in the ocean under ice, similar to deep-sea vents on Earth.
The interesting thing about these satellites is that in addition to the presence of liquid water, their surface sprays water jets, indicating the presence of hydrothermal activity. NASA’s Cassini space probe even discovered compounds containing carbon, nitrogen, and oxygen in Enceladus’s jet plume, as well as some components such as amino acids that make up proteins. Europa and Enceladus attract astronomers because their seafloor activities may be similar to the hydrothermal vents of our Earth’s oceans, and such an environment will potentially provide chemical conditions for life.
Frozen satellites on the surface may also promote the condensation reaction. Bagh said: “Even if you are in an icy satellite, you will experience the freezing and melting process of ice. Therefore, I think it is necessary to say that if the dry-wet cycle is important, then We should look for any environmental conditions in the solar system that may promote dehydration and oscillation.”
But to look for signs of ancient life, Demer and Dai defaulted to Mars as the planet where life is more likely to exist. The analysis of the deposit samples showed that there were hot springs and hydrothermal activities in the earth’s ancient times, which maintained the humid and dry cycle, which is essential for the coagulation reaction to breed life.
At present, many countries have proposed plans to explore Mars. NASA’s Perseverance rover will land on Mars’ Jezero crater in February 2021, looking for signs of ancient life, such as collecting minerals in rock samples. Although Mars and the “Bompass Hell” are 54.6 million kilometers apart, the difference between the two environments is not significant.