Our approach to the study of other worlds will be made through the media of liquid water. Water plays a multiple role in the environment and biology’s of Earth. On other planets, whose atmosphere may contain relatively large amounts of oxygen, water would almost certainly be an important raw material for organic compound synthesis.
It is believed that water is derived primarily from the crystallization of materials within the planet’s crust and is there after brought to the surface by geysers and volcanism. The ability of volcanism to release large amounts of water can be seen in the volcano Paricutin, during its most active period, it released 16,000 tons of steam a day (3,855,000 gallons of water daily). Measurements of gasses extruded from active volcanoes show a 68-70% composition of water vapor.
A reference to this process of water formation can be seen in the mineral albite (Na2.AlO3.6SiO2), a constituent of crystalline rock. At 1100ºC an pressures appropriate to 7500 feet below the planet’s surface, albite holds 4% water. As the energy from the planet’s formation is dissipated and radioactive decay diminishes the temperature begins to drop. When the subterranean temperature reaches 960ºC, crystallization begins. At 820ºC, one half of the albite has crystallized. The pressure of the newly released water build up and finally breaks through to the surface. Once in the atmosphere, it remains in its vapor state until the atmosphere is saturated at prevailing temperatures and pressure, there after condensation and precipitation begin.
The evaporation of water from the planet’s surface carries off large quantities of heat received from the parent star, thus helping to maintain a heat balance.
The atmospheric water vapor traps some of the infrared radiation which has been reradiated by the planet’s surface and provides the ‘greenhouse effect’. The effect of this trapped heat has increased Earth’s average surface temperature 30º-35ºC. Were it not for the greenhouse effect, our average surface temperature would be -10ºC (14ºF) instead of the mild 20ºC (68ºF) which it actually is.
The formation of a large cloud cover prevents further the loss of planetary heat and has the effect of depressing daytime temperatures and elevating night-time temperatures.
In the atmosphere, some of the water vapor condenses on dust particles, forming what will become rain. This process not only leads to a renewed water supply for the biotic community, but removes dust particles from the lower atmosphere.
Water and the Life Process
Water in its liquid state is the solvent and dispersion media for all protoplasmic constituents. It is only because of the presence of this chemical that the process of absorption, secretion and excretion are made possible. Carbohydrate production by chlorophyllic plants is dependent on water for the donation of a hydrogen ion in part of the photosynthetic activity.
The energy released from the foods (chemical mixtures) we eat, is largely is largely brought about by hydrolytic splitting of protein, fats and carbohydrates.
Amongst Earth’s biology’s, we find that there is a large circulation of water from the environment through the organism and back to the environment. During the life of a plant, the water lost through transpiration may be 200 to 1000 times its dry weight.
A normal human, in average environmental conditions, looses about 13 oz of water in expired air, 17 oz in urine and 20 oz from the skin in a 24 hour period (6-1/4 cups, minimum).
In general, the larger the animal, the more water is required for its survival. Water makes up 85-95% of the fresh weight of actively growing tissue; even dormant seeds are 5-10% water by weight.
It is biologically possible, that on small, warm, arid planets and on cold planets, where liquid water is not readily available, or where long periods of drought are experienced, that the percentage of water in an organisms cells may be somewhat less than found on Earth. Perhaps other methods of water retention or conservation would be in use, for example, water loss through evaporation might be small or entirely absent and higher life forms may be biochemically capable of using metabolic water (water derived from the oxidation of hydrogen in their food). These measures could also be coupled with the consumption of relatively high moisture foods, having a low protein diet and more concentrate urine.
Water is very important in the process of life and it will be found, in varying quantities, on all planet models explored in this study.
Continued in Chapter 2: Average Planetary Surface Temperature.
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