When looking for signs of life on extraterrestrial planets, the first thing to look for is whether there is water, whether there was water in the past, or the presence of an environment that could form water. In this sense, we think that water is indispensable for life and no one living in the world will have an objection. However, how and how much water really matters to life is not much known.
What is the importance of water for life?
From the smallest microbes to the largest animals, the lives of all living things on earth depend on water. Thanks to its many different features, it has shaped the surface and atmosphere of the Earth and played an indispensable role in the emergence and development and continuity of life. 71 percent of the Earth’s surface is covered with water; 97 percent of it is oceans and the rest is glaciers, arctic ice, lakes, rivers and so on. creates.
We can list the characteristics of water that make it extremely indispensable for the emergence and continuity of life:
1) Water is formed by covalent bonding of two hydrogen and one oxygen atom (H2O). Oxygen atoms are negatively charged and hydrogen atoms are positively charged. The bond between hydrogen and oxygen atoms is not linear. As a result of this structure, the water molecule has a polar structure as a charge. It can be said that there is a positive charge on one side and a negative charge on the other side. This polarity is the basis of the very important properties of water.
Water itself has intermolecular interactions and interactions with other substances in contact. Interactions between their molecules lead to a high surface tension on the water surface. The basis of this is the hydrogen bonds formed between molecules. It also tends to make similar hydrogen bonds with many different molecules, and a feature called adhesion that allows it to adhere to other materials emerges in this way. As the desire to bind to other molecules is greater than the interactions between their molecules, an effect called “capillary effect ve which causes the water to rise up in the tubes spontaneously occurs. Especially high trees remove the water they take from the soil up to their upper parts thanks to this feature of water. For example, a cypress tree is a tall tree and one of the important factors that it uses to extract water up to 30 m above the ground is the capillary action of water. Many plants that are much shorter use the water to carry the water upwards.
2) When water becomes solid (freezes), its density decreases. Thus, solid ice does not sink in liquid water. The fact that ice floats on the water surface is very important for the evolution of life. If the ice was denser than water, as the Earth cooled, the ice formed in the oceans would sink to the bottom and push the cold water below. It would sink again when the cold water froze upstairs. This would continue until all the water was frozen. Many seas and lakes would also be filled with ice. This was probably the end of life in the water. The evolution of life would have been prevented, especially given that the first life emerged in water.
3) Another feature of water is its expansion when it freezes. This feature is very important in terms of shaping land. Water seeping through the cracks in the rocks freezes and expands when the temperature drops at night. In the daytime, the air heats up and the water in the crack moves deeper. The night freezes again. The fragmentation of the rocks in this way causes the formation of soil. A large part of the plants developed on the soil.
4) Water with the highest heat capacity is the second molecule (after ammonia). This feature allows water to buffer (stabilize) heat fluctuations in the Earth’s atmosphere together with carbon dioxide. Thus, there is no immediate increase or decrease in temperature in the atmosphere.
5) Water is transparent. Incoming sunlight enters the water. Sunlight is indispensable for the development and survival of living organisms that perform photosynthesis.
6) Photosynthesis creatures break the water into oxygen and hydrogen by using solar energy. Hydrogen is used to make glucose by combining with the CO2 taken from outside and oxygen is given to the outside. Oxygen-breathing organisms also reverse this process and use oxygen and break down glucose to form water and CO2 again.
7) Water is called universal solvent. Salts, sugars, acids, bases and water-loving gases such as oxygen and carbon dioxide dissolve in water. Cell parts such as proteins, DNA and polysaccharides, which form the basis of life, are also soluble in water. Many metabolic activities in the body will take place in water. 60-70 percent of the human body consists of water. Similarly, this rate can be up to 90 percent in plants and up to 94-98 percent in some animals (eg jellyfish).
All these features reveal how much water is decisive for the emergence and continuation of life. Because of all these features, the first places in the study of extraterrestrial life have been the areas where water is thought to be in liquid form.