When contemplating the many forms of life, scientists must have an open mind and a rich imagination. Some researchers have even gone too far, for example, considering the possibility of dark matter as an extraterrestrial life! Indeed, it can seem very strange when compared to what we are accustomed to understanding. But in the right environment, some elements have enough potential to give birth to life, and we can see many such examples on Earth.
For example: arsenic. Arsenic is toxic to most life, but some seaweeds on our planet bind arsenic into complex organic molecules such as arsenic and copper arsenic acid. Other tiny life forms use arsenic to generate energy and help with growth. Sulfur can form very long, carbon-like molecular chains. Some bacteria survive by converting sulfur to hydrogen sulfide instead of oxygen. Phosphorus may even be a substitute because it is also able to form long chains with itself, and when combined with another common element in the universe, nitrogen, it has a great potential to form a wide variety of molecules.
Phosphorus is already a vital element to life on Earth, so it may be equally indispensable to life forms elsewhere, even examples of chlorine and nitrogen. Because these ideas are so foreign to us, researchers are likely to ignore the core signs of life's problems, even if they are close to them. One experiment asked participants to look for signs of life on Mars. While the subjects were busy studying photographs of the land surface, most of them did not see a single photograph of a waving orangutan.
The intent of the experiment was to show that when humans are bound by their own biases, tunnel vision is created, and if they are not actively looking, they often miss out on obvious signs. Our fixed perception of carbon may prevent us from recognizing its alternative forms, so we must be open to new possibilities and make bold assumptions, or we will most likely miss them, which is the case of non-carbon living.
Related knowledge:
Dark matter is a hypothetical form of matter that is thought to account for about 85 percent of the universe's matter. [1] A wide variety of astrophysical observations, including accepted theories of gravity, suggest that gravitational theories cannot explain gravitational effects unless there is matter other than our naked eye—suggesting the existence of dark matter. [2] For this reason, most experts believe that dark matter is abundant in the universe and has had a strong impact on its structure and evolution. Dark matter is called "dark" because it does not seem to interact with electromagnetic fields. This means that it does not absorb, reflect, or emit electromagnetic radiation (like light) and is therefore difficult to detect.
The case of carbon-free life
The periodic table currently has 118 known elements, and many more possible elements to be discovered. However, based on all these possible elements, astrobiologists still consider carbon indispensable to life and look for its signs when pursuing extraterrestrial life. However, in addition to our carbon sequestration, there are many substitute elements that can be used to support life.
All life we know is based on carbon, and there's a reason scientists think carbon is the most likely candidate for extraterrestrial life. Carbon is the main element of organic compounds on Earth, and life would not have existed without the unique capabilities of carbon. Stable chemical bonds can be formed between carbon and other elements including itself. In fact, it forms more compounds than any other known element, and nearly 10 million carbon-based compounds have been found in living things on Earth. Carbon is a fundamental component of carbohydrates, lipids, proteins, and nucleic acids, all of which are indispensable to life. If there is an element that elsewhere can form the basis of life, then it must satisfy some conditions.
Carbon has a huge diversity in the formation of compounds, so it is considered the king of elements. If an extraterrestrial life form is based on another element, a stable bond must be formed between that element and the various elements. All elements have electrons that rotate around the nucleus and form bonds when they share electrons with other elements. This element also needs to be sufficiently abundant in the universe so that it is not unusual to be found on any planet. Moreover, it should be able to self-circulate in some way, just as carbon does in the carbon cycle on Earth. Organisms need a way to excrete excess of this element and return it to their natural environment.
The best alternative to carbon seems to be silicon. Scientists mainly think this is because it is extremely similar to carbon. The outermost layer of carbon has 4 electrons and the elements tend to bond so that each atom has 8 electrons; this makes carbon the perfect pairing partner and an ideal companion for covalent bonds, in which carbon shares its own 4 electrons with other atoms, while other atoms also share their 4 electrons with carbon.
Silicon also has four electrons, and like carbon, it is abundant in the universe —one of the ten most abundant elements in the universe, and 135 times more abundant than carbon on Earth. Like carbon, silicon can also bind to oxygen and form long chains on its own. From this point of view, silicon is the most likely candidate element for the formation of non-carbon-based life. But why isn't life on our planet silicon-based? The reason is that while there are many similarities between silicon and carbon, silicon also has some drawbacks. The four electrons of silicon are located in the third orbital, while the four electrons of carbon are located in the second orbital, which means that silicon needs more electrons to be in a stable state, so the bonds formed by silicon are often weaker.
However, the bonds formed by carbon are very strong, and when paired with other carbon atoms, they can form the hardest known substance on Earth – diamonds. Silicon and carbon combine with oxygen (the basic building blocks of many life forms) to form different forms, respectively. Carbon combines with oxygen to form carbon dioxide, a gas that is easily excreted by organisms and circulated into the atmosphere. However, silicon combines with oxygen to turn into quartz, which is solid sand. For carbon-based organisms we're familiar with, it's hard to get solid sand out of their biological systems, so we think life forms based on other elements are unlikely to exist.
Limited by the fact that every life form we know of comes from Earth—and every life form on Earth is made of carbon—as an astrobiologist sees carbon as a possible sign of extraterrestrial life. But that doesn't mean that life forms based on other elements are impossible. We use the existence of earth-like conditions as a basis for assessing whether life may exist on other planets. However, planets that are actually much warmer than Earth would give silicon favorable conditions for life, because silicon can withstand temperatures much higher than carbon.
Scientists thought life would not survive harsh heat until they found extreme microbes living at temperatures of about 249 degrees Fahrenheit in the underground sea in the crater. Scientists also hypothesized that planets must be within habitable zones around their stars to have liquid water and temperatures associated with life, but with the possible subsurface oceans of planets such as Europa, Enceladus, and Titan hydrocarbon lakes, that assumption has also been questioned.
by: Wang Bu Liuxing, Du Shaohe, Matt