Cycles for Life
IF A city’s supply of fresh air and water were cut and its sewers blocked, disease and death would soon follow. Yet, our planet is a closed system—clean air and water are not shipped in from outer space, nor is waste matter rocketed out! So how does earth’s biosphere remain healthy and habitable? The answer: natural cycles, such as the water, carbon, oxygen, and nitrogen cycles, here explained and shown simplified.
The water (hydrologic) cycle involves three stages. 1. Solar power lifts water into the atmosphere by evaporation. 2. Condensation of this purified water produces clouds. 3. Clouds, in turn, form rain, hail, sleet, or snow, which fall to the ground, closing the loop. How much water is thus recycled annually? According to estimates, enough to cover the entire surface of the planet to a depth of more than three feet [100 centimeters].
↓ 3 ↑
↓ 1 ↑
The carbon and oxygen cycles involve two key processes—photosynthesis and respiration.* Photosynthesis uses sunlight, carbon dioxide, and water to produce carbohydrates and oxygen. Respiration, which occurs in animals and humans, combines carbohydrates and oxygen to produce energy, carbon dioxide, and water. Thus, the output of one cycle is the input of the other, and it all happens cleanly, efficiently, and quietly.
The nitrogen cycle is essential to the production of amino acids, proteins, and other organic molecules. A. The cycle begins when lightning and bacteria convert atmospheric nitrogen into compounds that can be absorbed by plants. B. Plants, in turn, incorporate these compounds into organic molecules. Animals that eat plants thus also acquire nitrogen. C. When plants and animals die, another family of bacteria break down the nitrogen compounds, releasing nitrogen back into the soil and the atmosphere.
← ← ← ← ← ← ← ← ← ←
↓ Earth’s atmosphere is ↑
↓ 78 percent nitrogen ↑
↓ ↓ Organic ↑
↓ A ↓ molecules ↑
↓ Bacteria ↓ B ↑ ↓ C ↑
→ Nitrogen compounds Bacteria →
→ → →
Consider: Humans, with all their technology, create countless tons of unrecyclable toxic waste annually. Yet, the earth recycles all its wastes perfectly, using ingenious chemical engineering. “Chance processes alone almost certainly could never have duplicated” such environmental harmony, says religion and science writer M. A. Corey.
Giving credit where it is due, the Bible says: “How many your works are, O Jehovah! All of them in wisdom you have made.” (Psalm 104:24) That wisdom has been manifest in a special way toward humankind.
The cycles of various chemical elements may combine or overlap. Oxygen, for example, is present in carbon dioxide, carbohydrates, and water. Hence, it shares in both the carbon and the water cycles.