Beijing time on January 16, according tomedia reports, we can easily distinguish what is life, they will move, grow, eat, excrete and reproduce. Biologically, understanding life is also simple, and researchers often use the acronym “MRSGREN” to describe them as motion, breathing, sensitivity, growth, Reproduction, excretion , and nutrition.
But among us we may live in some undiscoverable form of alien life. Is that possible?
Although life is easily recognized, it is notoriously difficult to define it. Scientists and philosophers have argued for centuries, even thousands of years. For example, a 3D printer can replicate itself, but we don’t call it a living thing. On the other hand, the infertility of a mule is well known, but we would never say it is not life.
There is so much debate that there are more than 100 definitions of life. One (imperfect) definition is to describe life as “a self-sustaining chemical system that adapts to Darwinian evolution”, which applies to many of the situations we want to describe.
The lack of definition is a major problem in the search for life in space. It’s different from “when we see it, we’ll know it.” The inability to define life means that we limit our own imagination of life to earth-centric, and perhaps even human-centered. When we think of aliens, we often think of humanoids, and the intelligent life we’re looking for isn’t necessarily similar to humans.
Life we don’t know
A lot of people believe in aliens, will they be made of carbon and nitrogen like you and me? Maybe not. It’s possible that they’re here right now, but we can’t see them.
Such life will exist in a “shadow biosphere”. This does not refer to the ghost kingdom, but to creatures that may have different biochemical properties but have not yet been discovered. This means that we cannot even understand or even notice them because they are beyond our understanding. Assuming this life exists, the shadow biosphere in which it is located is likely to be microscopic.
Then why haven’t we found them yet? In fact, our methods of studying the microcosm are limited, and only a small number of microbes can be cultured in the laboratory. This suggests that there may indeed be many life forms that we have not yet discovered. We do now have the ability to sequence the DNA of non-cultured microbial strains, but this can only detect known life, i.e. life containing DNA.
However, if we find such a “shadow biosphere”, should we call it an “alien”? It depends on whether an alien or just a “strange creature” is “from an alien.”
A popular view of extraterrestrial life is that the biochemical properties of these lives may be based on silicon, not carbon. Even from the point of view of Earth’s centrism, this argument makes sense. About 90 percent of the earth’s material is made up of silicon, iron, magnesium and oxygen, meaning there are many things that can be used to create potential life forms.
Silicon, like carbon, also has four electrons that can be bonded to other atoms. Silicon is heavier, with 14 protons (protons and neutrons make up the nucleus), while carbon nuclei have six protons. Carbon can form powerful double and triple bonds, forming long chains, enabling many life functions, such as building cell walls. Silicon, by contrast, is much more difficult. It is difficult to form strong chemical bonds, so the stability of long-chain molecules is much worse.
What’s more, common silicon compounds, such as silica, are usually solid at land temperature and insoluble in water. In contrast, carbon dioxide is highly soluble and more flexible, providing more molecular possibilities.
There is a fundamental difference between life on Earth and the composition of the earth as a whole. Another objection to the silicon-based shadow biosphere is that too much silicon is locked in rocks. In fact, the chemical composition of life on Earth is similar to that of the sun, with 98% of the atoms in living things consisting of hydrogen, oxygen and carbon. So if viable silicon life forms existed on Earth, they might have evolved elsewhere.
Still, there are some arguments for the existence of silicon-based life on Earth. Nature has a strong adaptability. A few years ago, scientists at the California Institute of Technology successfully developed a bacterial protein that binds to silicon and essentially gives it life. Thus, although silicon is less flexible than carbon, it may find ways to assemble organisms or bind to carbon.
When it comes to other parts of space, such as Saturn’s moon Titan or planets orbiting other stars, we certainly can’t rule out the possibility of silicon-based life. To find them, we must somehow jump out of the box of terrestrial biology and find ways to identify new life forms. These life forms are fundamentally different from carbon-based life forms. Like researchers at the California Institute of Technology, other scientists are doing a lot of experiments to test these different biochemistrys.
Although many people believe that life exists elsewhere in the universe, we have no evidence to prove it. Therefore, it is important to consider all life as valuable, regardless of its size, quantity or location. Earth supports the only known life in the universe. Therefore, regardless of the form of life in the solar system or elsewhere in the universe, we must ensure that they are protected from harmful pollution, whether they are closer to Life on Earth or completely alien to extraterrestrial life.
So is it possible that aliens are among us? We haven’t had a life with space-crossing technology. However, there is some evidence that carbon-based life molecules can reach Earth through meteorites. Therefore, we certainly cannot rule out the possibility that there are more strange forms of life on Earth.