If there is life on the planet Mars it will have to stand extreme cold at night. This should not be too difficult for plants. Cold-country plants on earth tolerate arctic conditions for some months each winter, and plants that grow on high mountains in the tropics survive temperatures which frequently fall below freezing point during the night. Large animals on earth try to keep from freezing point during the night. Large animals on earth try to keep from freezing, but many insects spend the winter in frozen surroundings. Bacteria, protozoa and other small organisms can be kept frozen for many years and thawed out alive and healthy. So life on Mars should not have too much trouble with cold. An obvious way to avoid short-period cold of the Martian would be to burrow into the ground as many cold-country animals do on earth.
Another difficulty for life on mars is scarcity of oxygen and water, but these lacks may not be as serious as they appear from the human point of view. Perhaps an atmosphere like the earth’s is aluxury, not a necessity. Martian plants might have strong impervious skins to keep the moisture in their tissues from evaporating into the thin, dry air. If they need oxygen when the sun is not shining,as the earth’s plants do, they may store it as a gas or as some oxygen-rich chemical compound. They would need some way of absorbing a little carbon dioxide, but in other respects they could live for most of the time independently of the atmosphere. In the moist Martian springtime they would absorb enough water to last them until the following year, and during the same season they would probably do most of their growing and reproducing.
Martian animals would have a tougher time, but if there are plants on Mars, there must be animals of some sort. An animal, by the scientist’s definition, is an organism that eats plants, using part of the plant’s material to build its own body and the rest to burn for energy. We usually think of animals, including men, as preying on plants, but if we choose, wecan think pof them as the plants’ benefactors. If there were no plant-eating animals on earth, not even bacteria, the plants would grow until they had absorbed all the carbon dioxide in the atmosphere. Then they would die.
We can only guess what Martian animals may be like. They may be as small as bacteria, or there may be larger animals that move very slowly, a few inches per day, because the scarcity of oxygen permits their muscles to generate only a little energy. Or perhaps Martian animals may depend on the oxygen that the plants have accumulated for their own use. After one of these animals had eaten a plant and its oxygen, it would be able to move comparatively fast and creep to another oxygen-yielding plant.
Both Martian plants and animals might cope with water scarcity by storing water in special containers, as do many plants that live on the earth’s deserts. But some biologists suggest that may have learned how to get along with practically no water.They must have some liquid in them to bring about the chemical reactions necessary for life and growth, but it need not be water. It might be some other fluid like glycerine that would not freeze easily in Martian cold or evaporate into the dry Martian atmosphere. The plants could make it themselves as they make all sorts of complicated chemicals. Animals that eat the plants would take the liquid too and use it as the vital fluid in their own bodies. The freezing point of water, so important on the earth, would not mean much to creatures with such a fluid in their veins and tissues. They could keep active even with their body temperatures far below zero. They could thrive for years on waterless deserts where the air is almost totally dry.