Shulou(Shulou.com)11/24 Report--

This article comes from the official account of Wechat: SF Chinese (ID:kexuejiaodian), author: SF

People always discuss whether the egg comes first or the chicken comes first. It seems that it is more reasonable to have eggs first, because eggs can hatch chickens. So here comes the question, where did the egg come from? This is actually a question of the origin of life.

/ Zhao Jiaming / tr. by Phil Newell)

Production / editorial Department of Science focus

01. The origin of life, opinions vary.

Stromatolites from Shark Bay, Australia. Stromatolites are usually created by microbes, especially cyanobacteria, which are one of the earliest forms of life on Earth, but scientists do not know how such "early ancestors" came into being. (photo source: Paul Harrison)

The question of how life originated has been perplexing scientists and even an unsolved mystery that the public is most concerned about every day. Although Darwin's "theory of evolution" explains the evolution of life from lower to higher, it still cannot explain how the "ancestor" of life on earth came into being. Therefore, scientists have put forward a variety of hypotheses.

Some people think that life originates from inanimate matter in nature, and you can understand it as "life pops out from a crack in a stone"-the theory of abiogeny; some people think that life comes from outer space, and that meteorites hit the earth, bringing life matter from outer space-some people think that life comes from RNA-- 's "RNA world" hypothesis. They believe that DNA uses RNA to synthesize proteins, so there may be some RNA on Earth in the early days, which can also synthesize proteins. You know, protein is the foundation of life.

02. Is "a bowl of soup" the cradle of life?

The earliest known life on Earth was some microbes, which were found near undersea hot springs. These microbes may have lived as early as 4.28 billion years ago, while the earth was formed only 4.5 billion years ago.

Each of these hypotheses has its own reasons, and no one can convince the other. Among them, the most widely accepted is the "primitive soup" hypothesis that "life originated from undersea hot springs". In short, life originated from the "bowl of soup" of the primitive earth.

Undersea hot springs are also called seafloor hydrothermal vents because they look like chimneys with black or white smoke standing on the sea floor. The solution ejected from these vents is hot and salty, and the nearby water temperature can reach 400 ℃. In theory, there can be no life at such a high temperature. How can anyone still think that life originated from undersea hot springs? Scientists believe that this has something to do with the composition of the early Earth's atmosphere. You may already know that the earth's atmosphere is made up of nitrogen, oxygen, carbon dioxide, ozone and other gases. Ozone forms the ozone layer and can isolate ultraviolet radiation. However, the composition of the earth's atmosphere in the early days was different, when the earth's atmosphere did not contain ozone, so the ultraviolet radiation on the earth's surface was particularly intense. It is impossible to give birth to life in such an environment. However, the situation at the bottom of the sea is different-sea water has replaced the current role of the ozone layer, putting on a layer of "protective clothing" for life. The sea floor has become a hotbed for the birth of life on earth.

Then why is it assumed that life originated from undersea hot springs? If you compare biology to a machine, if you want it to work properly, you need energy to drive it, either to burn gasoline or coal. The same is true of living things, which need energy in order to function properly. In high school biology class, we have all learned that there is a kind of organelle called mitochondria in cells, which is the place to provide energy for living things.

Scientists have found the directional movement of hydrogen ions near undersea hot springs, and mitochondria use the directional movement of hydrogen ions to generate energy. As a result, scientists who argue that life originated in undersea hot springs believe that creatures living near undersea hot springs get energy in exactly the same way that mitochondria produce energy. In this way, early life had an energy source in the origin of undersea hot springs, coupled with a large amount of solutions containing C, H, O and metals from the vents of undersea hot springs, which provided a material basis for the origin of life.

With materials, energy, and safety, this is like making a pot of soup, ingredients and stoves are ready, light the fire to cook soup and wait for delicious soup to come out of the pot.

Life is like this pot of soup, probably originated near the undersea hot spring. After all, such a perfect condition has never been found in any other environment.

03. The cornerstone of the path of the origin of life is near the undersea hot springs, and the existence of material and energy sources that make up life, coupled with a suitable environment, can prove that life originated from undersea hot springs? The answer is no. There is another key element that we still don't know-catalysts, the chemical reactions that produce living matter require the presence of catalysts.

A study published in Nature Communications (Nature Communication) in February 2023 identified important "enzymes" in the origin of early life, adding new evidence to prove that life originated in undersea hot springs.

Scientists at the Max Planck Institute for Immunobiology and epigenetics in Germany used nanoparticles of Ni-Fe alloy to catalyze the conversion of hydrogen and carbon dioxide to formates, acetates and pyruvate at 25 °C and 2.5 MPA. In addition, pyruvate labeled by Cmur13 can be further converted to acetic acid, p-pyruvate and lemon malic acid within an hour at room temperature. These are important intermediates of acetyl-CoA pathway, which is one of the oldest pathways to fix carbon dioxide, and many microbes grow in this way, as may be the case in early life.

Using CMel 13 labeling, the scientists found that carbon dioxide immobilization products include pyruvate, acetate, p-pyruvate and lemon malate catalyzed by Ni-Fe alloy. In previous studies, scientists have known that carbon dioxide and hydrogen can be quickly converted to formates, acetates and pyruvate through the acetyl-CoA pathway catalyzed by enzymes. Near the seafloor hot springs, even if there are no enzymes, Ni-Fe alloys can act instead of enzymes to form intermediate products of acetyl-CoA, linking carbon dioxide immobilization and the tricarboxylic acid cycle (an important reaction cycle that ensures the functioning of life, related to the metabolism and synthesis of living substances).

Other studies have found that some microbes can grow normally even without tricarboxylic acid cyclase.

However, scientists have not found a link between carbon dioxide fixation and the tricarboxylic acid cycle. This study makes up for this-through the Cmur13 labeling, it is found that pyruvate can rapidly convert acetic acid, p-pyruvate and lemon malic acid under the catalysis of Ni-Fe alloy, and participate in the tricarboxylic acid cycle. This proves that high carbon number organic compounds can be obtained by the fixed reaction of carbon dioxide under the action of natural metal catalysts, which is the basis of life. Primary metal and hydrothermal alloy nickel-iron ore can replace the functions of several enzymes in the biological pathway. In other words, there are also enzymes near undersea hot springs that catalyze the formation of living matter, which adds solid evidence that life originated from undersea hot springs.

Now you know that the seafloor hot springs in the early earth's oceans had the most suitable environmental conditions for the birth of life at that time, and life may have originated from undersea hot springs. However, these are all hypotheses put forward by researchers, and like the previous hypotheses, there is no direct evidence to prove that although there is evidence of relevant research, they do not belong to direct evidence and need further research and discovery by researchers.

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