Astronomers have been working hard to find evidence of the existence of extraterrestrial microorganisms. On Mars, Europa...any place in the solar system that has the conditions is the object of their search. But the most exciting progress in the search for extraterrestrial life in recent years has been made on Earth. Exobiologists have come to the harshest and most extreme places on earth, in the driest Atacama Desert in Chile, in caves with the harshest environments, under the thousand-year ice shelf in Antarctica, and in the deep sea of ??several kilometers. Below, at an altitude of tens of thousands of meters, they discovered a variety of isolated bacteria whose tenacity amazed scientists. In the ancient frozen rocks of Antarctica, there is a kind of bacteria hiding comfortably in the porous space under the surface of the stone, living as vigorously as the morning glories in the flower shop window; French scientists once found that 3,000 meters below the Pacific Ocean, the water temperature is as high as A variety of bacteria were found in hot springs at 250°C; the "Apollo 12" spacecraft that landed on the moon in 1969 recovered the camera left on the moon by the unmanned exploration ship "Observer 3" two and a half years ago, and discovered that it was At the bottom is the microorganism "Streptococcus mitis" on the earth. This microorganism from the earth has survived for two and a half years on the nearly vacuum and cosmic ray-filled lunar surface!
Many types of bacteria do not require air, either by breaking down (rather than oxidizing) organic food, or by obtaining oxygen from oxygen compounds such as sulfates or nitrates rather than from the air; some bacteria Convert iron compounds and sulfur to maintain the continuation of life and survive; some bacteria grow in boiling water; some bacteria survive in salt water below 0°C; some bacteria survive under incredible high pressure. It seems that the lives of most bacteria are endless, and the spores of some bacteria can lie dormant for thousands of years.
Their life potential is completely or almost different from the potential of other life on earth. It is this difference that suggests to us another possibility of life, perhaps another possibility of life on other planets in the universe.
Countless possibilities for life
Since bacteria on Earth exhibit such a rich variety of life forms, how many possibilities are there for life in the universe? Life on earth is composed of nucleic acids and proteins, but is this the only form of life? Could there be other life forms based on other chemical bases?
This problem is undoubtedly a major challenge for biologists. Because "protein life" on earth is based on carbon, some scientists turned to the periodic table to see which element had the properties most similar to carbon - of course silicon in the same family. Silicon-based life can even maintain its life by absorbing starlight from the universe without ingesting organic matter. Its body is composed of most light particles and a small number of material particles. Material particles can also be converted into light particles when necessary. It can be imagined that since the exhaust gas exhaled by us carbon-based creatures is carbon dioxide, then the silicon-based creatures on Mars should exhale silicon dioxide, a compound of silicon and oxygen. Silica is actually the sand we usually see on the beach. In other words, what these Martian creatures emit are sand grains when they breathe!
Some science fiction writers have also noticed that sulfur in the periodic table of elements has many similarities in properties with oxygen in the same group. Does that mean that on some warmer planets (sulfur is solid at room temperature on Earth), the oxygen needed for biological respiration can be replaced by sulfur?
In addition, water is the solution and medium necessary for all protein life. Is there any other compound that can take the place of water? have! That's ammonia. Since ammonia is still liquid below the freezing point, some science fiction writers have speculated that there may be oceans composed of ammonia under the surfaces of some cold giant gas planets, and the oceans are filled with life forms using ammonia as a medium.
The above are just individual and sporadic ideas. What truly comprehensively investigated and systematically analyzed the problem was an article "It's Not Us" written by the famous biochemist Asimov. Known”.
He proposed six life forms in the article:
1. Fluorinated silicone organisms using fluorinated silicone as the medium;
2. Fluorinated sulfur using sulfur as the medium Biology;
3. Nucleic acid/protein (based on oxygen) using water as the medium;
4. Nucleic acid/protein using ammonia as the medium (based on nitrogen) ) organisms;
5. Lipoid compound organisms using methane as the medium;
6. Lipid compound organisms using hydrogen as the medium.
The third item is what we are familiar with—and the only thing we know—life. As for the first and second items, they are life forms that may exist on some high-temperature planets. In addition, the anaerobic archaea that once appeared on the earth and lived in sulfur mines are likely to use sulfur as their life form. medium; and the fourth to sixth items are biological forms that may exist on some cold planets.
Life in the universe may have different chemical bases, which makes us realize that life has different adaptability to the environment - the so-called "A is like bear's paw, B is like arsenic", we think it is comfortable A hospitable planet may be unbearably hot for some creatures and unbearably cold for others.
More incredible ideas
However, science fiction writers are still not satisfied with the diversity of life. They gave full play to their imagination in their respective works and created some more incredible ideas for us. , but upon closer consideration, it seems to be a world of life that makes sense. Some writers imagine that there may be life forms based on liquid helium and connected by superconducting currents on some extremely cold planets; other writers believe that even in the cold and dark depths of space, There may also be some highly intelligent creatures that are composed of interstellar gas and dust and transmit neural signals through radio waves - Hall's science fiction novels are masterpieces in this regard; some writers with more imaginative imagination even think that alien life may be possible There is no need for chemical basis at all, they may just be some life forms of pure energy, such as a beam of electric waves.
The most interesting one is "Dragon Egg" written by the famous science fiction writer Forward. This well-conceived work describes the creatures on the surface of a neutron star. This neutron star is only 20 kilometers in diameter, but its surface gravity is 67 billion times that of the Earth, its magnetic field is 1 trillion times that of the Earth, and its surface temperature reaches more than 8,000 degrees Celsius. What creature can survive in such an environment? It is an organism composed of "degenerate nuclear matter". The so-called "degeneracy" means that the electrons outside the atom are squeezed into the nucleus, so all the atoms can be very close together, forming an ultra-dense substance. Creatures on neutron stars are about half a millimeter tall, half a centimeter in diameter, and weigh 70 kilograms. This is because they are composed of degenerate matter. In addition, their metabolism is based on nuclear reactions rather than chemical reactions, so the rate of all changes (including birth, old age, illness, death and thinking) is 1 million times faster than that of humans!
Let’s take a look at an interesting speech given by a medical graduate at a graduation ceremony: Somewhere on the other side of our galaxy, there is a distant planet, far away from a planet whose level and temperature The stars are just right and neither far nor near. At this moment, there is a committee meeting up there, studying our little remote solar system. The conference has been going on for a year and is now coming to an end. The intelligent beings of that place were signing a document (with some number, of course) that asserted that life was unthinkable in our place and that this place was not worth the expedition. Their various instruments have discovered that the most deadly gas exists here, which is oxygen. In this case, everything is lost.
This is not just random imagination, anaerobic organisms exist on the earth. For them, oxygen is not only not essential, but a deadly "poison". If oxygen is the most important thing to humans on earth, why do we have any reason to think that only planets with an environment comparable to that of earth can produce life?
Today, although mankind’s search for extraterrestrial life is still empty-handed and nothing has been found, we should still persist in the search. At least, it has greatly expanded our understanding of the biological principles of the universe.