2023-09-26 04:00:10
We often hear that the day the Sun goes out, life will stop. But since it is considered to be “mid-life”, let’s live peacefully for a few more billion years. However, without its light, there would be no earthly life as we know it. So what is so fundamental regarding light for life?
Image d’illustration Pixabay
For humans, as for animals, food, essential to life, depends on the plant world. This remains true for exclusive carnivores, which are at the top of the food chain. Plant growth occurs through photosynthesis (Greek φῶς phĹŤs, light and…), a chemical process that needs light (what the Greek root “photo” says). Photosynthesis transforms carbon dioxide (CO2), by releasing oxygen (O2, also known as “di-oxygen”); carbon (Carbon is a chemical element of the family of crystallogens, symbol C,…) stored and a supply of water allow the synthesis of sugar molecules, essential for plant growth.
It is the Sun which provides this light, even if artificial lighting, achievable on a small scale (a lighted cellar for example), also allows photosynthesis. Another condition usually considered necessary for life is the presence of oxygen. It is very probably the photosynthesis of primitive forests which led to the abundant presence (~20%) of oxygen in an atmosphere which was undoubtedly originally devoid of it.
Whether for food or for respiration, living beings need to maintain and build complex structures (large molecules like DNA, cells, or organs in animals). Building such a vital organization (An organization is) requires an input of energy (In common sense, energy designates everything that allows work to be carried out, to produce…).
While it is possible to live without light for a while, the sun is essential to our survival.
Andreiuc88/Shutterstock
It is the essential role of sunlight to provide this energy. The Sun is therefore a source of light energy, which is transformed into chemical energy in photosynthesis. When we feed, it is this chemical energy stored in food, often counted as food calories, that keeps us alive. Likewise, when we breathe, it is the oxygen in the air which allows us to carry out chemical transformations, which are also essential to life. So, can there be life without light? Maybe ! But you always need a source of energy, essential for metabolism. Research on extremophiles opens up interesting perspectives from this point of view. These are living organisms, most often on the bacterial scale, which survive in conditions known to be very hostile to life (temperature above 100°C, very high pressure (Pressure is a fundamental physical concept. We can see it as a reported force…), extreme acidity or salinity: there is even life in the Dead Sea (The Dead Sea is a salt water lake in the Middle East. With an approximate surface area of 1050 km²,…)!).
Few interactions with the entire living world seem necessary for these very particular organisms: they do not seem to depend, unlike us, on the plant world, for which light is essential. These undoubtedly use purely terrestrial resources, such as the heat of volcanoes, or the salinity of lakes (ionic exchanges, a bit like battery energy).
Plant photosynthesis consists of reducing carbon dioxide from the atmosphere through water absorbed by the roots using solar energy (Solar energy is the energy that the sun releases through its radiation, directly or of…) captured by the leaves with the release of oxygen in order to produce carbohydrates.
TPEphotosyntheseartificielle/Wikipedia, CC BY
Some scientists even imagine that it is in these types of hostile circumstances that primitive life would have appeared, but for most of them, it is light which is the first source in the proliferation of life, and Rather, it is Darwinian vital evolution that has enabled these very special adaptations to extreme environments.
So can humans live without light for an extended period of time? At the bottom of a mine, or a cave, miners or speleologists know how to survive, even without any light, but staying alive consumes energy, which is stored in food and this comes from solar light.
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