Is there life on our sister planet Mars? Of the many questions about our uni verse for which the United States space program seeks answers, this is probably the one of greatest interest to most people. The final answer is still forthcoming, but the evidence indicates that the existence of life on Mars is doubtful because of an absence of something so common here on earth that we scarcely pay any real attention to it—water.
The preliminary data appeared promising when the Mariner 9 mission was sent aloft in 1971 to photograph the red planet and test for such items as temperature conditions, composition of the atmosphere, and presence of the all-important liquid, water. Results showed evidence of an atmosphere conducive to living processes. Temperatures were within the life-supporting range, and photographs showed what appeared to be massive polar ice caps and dry river channels. But Mariner 9 also returned pictures of immense dust storms, indicating the planet is dry.
In 1976 the Viking spacecraft landed on the Martian surface with sophisticated instruments. Crucial tests, scientists hoped, would confirm the desired presence of life. But results were inconclusive, and the dry, barren landscape revealed in transmitted photographs suggested strongly that Mars is lifeless.
Water and life are close companions. An environment without water is an environment devoid of life. The difference between earth and the arid moon, or the verdant meadow and the barren desert, is largely the effect of water. This commonplace but quite extraordinary liquid forms a major portion of all living organisms and is necessary to numerous vital physiological processes. With the exception of dry seeds, in which the water content may be as low as 2 per cent, living things consist of from 40 to 95 percent water. For example, the human body is about two thirds water.
A close look at the water molecule's unique suitability for its various life-supporting roles leaves one with the compelling impression of a Master Intelligence behind its creation. Consider first its chemical structure. Water is a small, simple molecule consisting of one atom of oxygen and two atoms of hydrogen FfaO. Its relative size can be better appreciated by comparing its molecular weight of 18 with that of one of the smallest proteins, insulin, which has a molecular weight of 5,733. The small size of the water molecule is of great significance since it allows the membranes of living cells to retain the larger molecules that make up their own con tents while at the same time permitting water to pass through freely.
The arrangement of the three atoms in the water molecule is such that the molecule, though electrically neutral, is polarized, having both a positive and a negative pole. Its neutral charge allows it to enter into chemical processes within the cell without altering the cell's delicate ionic balance. But its polarity allows the water molecules to interact with one another, forming loose bonds and thus creating a continuous water film. This creates the surface tension that enables a needle to float if carefully placed on the water's surface or a water strider to glide smoothly over the surface of a pond. The cohesive quality of water that results from this bonding of molecules, combined with its adhesive property (which also derives from its polarity) is frequently demonstrated in the sticking together of glass slides or drinking glasses that have been put together wet. This adhesive property makes water a most efficient wetting agent.
But water cohesiveness has far more important consequences. It allows numerous tiny water drops to come together high in the colder atmosphere and form large drops that are heavy enough to fall to the ground before they vaporize. Without such a coalescing of drops there would be no rain, since water would remain in the atmosphere as a vapor. Also, it is the cohesiveness of water that allows a tree to absorb water from the soil in much the same way that water is pulled up a drinking straw. The thin water columns moving up the tiny tubes, or xylem vessels, in the roots and stems are pulled upward by negative pressure (suction) created in the leaves by the evaporation of water from their surfaces. The equivalent of about 20 atmospheres of negative pressure is required to pull water to the top of a giant redwood tree. Without tremendous cohesive forces the water column would break, flow would cease, and tree growth would be limited to only a few feet.
Several other physical properties of water seem to have been designed for a life-supporting system. One such property is its very high specific heat, which allows water to absorb large amounts of heat without a proportionate rise in temperature. This property is readily seen when water is heated in a kettle. The metal gets hot in a few minutes while the water slowly heats to a boil. Not only does water heat slowly, it also cools very slowly. As a result, living things, which contain a proportionately large amount of water, can maintain a fairly constant body temperature amid fluctuating environmental temperatures. For the same reason ocean-living creatures enjoy a uniform temperature even when atmospheric temperatures range widely. Like wise, its high heat of vaporization allows water to remove large quantities of heat from surfaces as it evaporates, thus, functioning as an efficient coolant. The perspiration of animals or the loss of water from a plant (transpiration) on a hot day are examples.
Water's tremendous solvent property is also an important part of its life-sup port role. Water is known as the universal solvent because it is capable of dis solving a wide range of substances. The importance of this fact becomes evident when one realizes that all substances that pass in and out of living cells do so only as they are dissolved in water. The food we eat, the substances stored in seeds to feed the growing seedling, the waste products of metabolism—all must go through the bodies of living organisms in solution. Without this amazing liquid, living things could neither absorb food nor eliminate chemical waste and there fore could not survive. This unusually efficient solvent property results from the polarity of the water molecule and makes it an indispensable washing agent.
Another property of water with wide-ranging and important consequences for living things is its ability to exist in different physical states at normal atmospheric temperatures. Liquid water is continually being converted to a vapor until the air becomes saturated. This vapor then condenses back to the liquid state and falls as rain. During this cycle, air currents carry water over long distances from lakes and oceans and dis tribute it over the earth to make life possible and to promote growth and beauty.
When sufficiently cooled, atmospheric water vapor crystalizes into snow, and liquid water solidifies into ice. In this solidified state the water is retained on the surface of the ground, where rising temperatures cause it to slowly melt and supply necessary water for plants and animals. Much of the earth's fresh water is stored in this solid state, especially in the expansive ice sheets and permafrost that characterize the polar regions.
Indeed, the relative stability of the earth's temperature is largely due to the effect of water vapor in the atmosphere, which, by its high specific heat, maintains a blanket of warm vapor around the earth and prevents atmospheric heat from radiating back into space. It is the low water content of the cloudless skies of desert regions that gives these climates their wide daily range of temperature. The difference between day and night temperatures in desert areas may exceed 50 degrees.
One of the most amazing phenomena associated with water is its behavior as it cools toward the freezing point. Most materials contract on cooling, reaching their greatest density at freezing. But water behaves differently. Like other liquids, it contracts as it cools to 4 C; then it begins to expand until it freezes at 0 C. This expansion decreases the density of ice compared to water, allowing ice to float. Thus lakes and rivers freeze at the surface instead of upward from the bottom, and the living creatures within them remain alive in relatively warm water even when the surface is frozen solid.
In order to avoid oxygen deficiency for aquatic life forms when the surface of a lake is sealed with ice, the Master Designer provided water with another interesting quality. The ability of water to absorb oxygen increases as the temperature decreases. For example, the solubility of oxygen in water at 0 C is approximately twice that at 30 C. This is the reason why fish are usually much more abundant in cold water than in warm tropical waters.
Water is vital to the existence of every form of life. Its great abundance and its natural ease of circulation make it accessible to living things everywhere. It has no taste to create excessive craving by some creatures or rejection by others. For the same reason, it has no smell and no color. Imagine taking a bath in red or yellow water, or of drinking water with a sweet, sour, or any other taste! Strangely enough, the two compounds most similar to water in molecular structure, hydrogen sulphide (H2S) and ammonia (NHa), are both pungent gases with strong acid/base reactions, forbid ding in taste and smell, and toxic to living cells at relatively low concentrations.
Since most animals, unlike plants, must take in water voluntarily by drinking, the Master Designer created in animals a mechanism for sensing when the water level of the body needs to be replenished. In the vertebrate brain this "thirst center" is located in the hypothalamus and functions to create a sensation of thirst when the body's water supply runs low. Once the thirst is satiated the inclination to drink ends, preventing oversaturation of the system.
Closely associated as water is with life, it is not surprising that the Bible so often uses it as a symbolic ingredient of spiritual growth and rejuvenation. Thus the prophet Isaiah invites all who are spiritually thirsty to drink of the water of life (Isa. 55:1) and Jeremiah chides the Israelites for forsaking God, the "fountain of living waters," and building for themselves broken cisterns that can hold no water (Jer. 2:13). Speaking of His promised gift of the Spirit, God, through Isaiah, said, "I will pour water upon him that is thirsty" (Isa. 44:3), and the final outpouring of the Spirit upon the church is depicted as rain—the latter rain (Hosea 6:3).
In His discourse with the Samaritan woman Jesus promised that whoever drinks of the water that He gives shall never thirst, but that the water shall be come in him a well, springing up into eternal life (John 4:14). The cleansing of the sinner and his rebirth into the kingdom of God is symbolized by washing with water at baptism. Thus Jesus told Nicodemus, "Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God" (chap. 3:5).
At the beginning of Creation God's Spirit moved upon the waters and formed a beautiful, habitable earth out of the great deep (Gen. 1:2, 6, 7). In the garden paradise of Eden, man's first home, a river flowed to water the Garden and the surrounding country (chap. 2:10). Thus from the beginning, water and life and beauty have been inseparable companions.
We may take this extraordinary liquid for granted, but the barren view of a lifeless, dry Martian landscape is enough to remind us of God's wise gift of such a commonplace thing as water. Even today, after ages of degeneration, much of earth's original beauty can still be seen in mountain streams and quiet lakes, in roaring rivers and tranquil bays. And many a weary soul still finds his spirit lifted by listening to the quiet babbling of a woodland brook or watching giant waves break against a rocky coast. Even eternity would not be perfect without an abundance of water. In his vision of our future home John saw "a pure river of water of life, clear as crystal, proceeding out of the throne of God" (Rev. 22:1).
