Natural Resources

All life depends on three natural resources held together by the Sun. Air is a mixture of gases, mainly nitrogen and oxygen, that supports breathing and burning and keeps the planet warm. Water covers most of the Earth and fills every cell of every living thing. Soil is the thin top layer made over thousands of years from broken rock plus the remains of dead plants and animals (humus); it holds the nutrients and water that plants need. These resources are not endless, and once polluted they are slow and costly to clean.

The same atoms are used over and over. The movement of an element such as carbon or nitrogen between living things, the air, water and soil, and back again, is called a biogeochemical cycle. In the water cycle the Sun evaporates water from the sea, it forms clouds, falls as rain, and rivers carry it back. In the nitrogen cycle, nitrogen gas is fixed into nitrates by lightning and by bacteria, plants take it up, animals eat the plants, and other bacteria release it back to the air. The carbon and oxygen cycles work through breathing and photosynthesis. Nothing is wasted; nothing is created fresh.

Carbon dioxide in the air is taken in by green plants during photosynthesis and built into food. Animals eat that food and release carbon dioxide back when they respire; burning fuels and decay return more. Oxygen has the opposite story: it is used up by respiration, by burning and by the rusting of metals, and it is put back into the air almost entirely by photosynthesis. So plants quietly keep both gases in balance, which is why too much burning of fuel upsets the climate.

High up in the stratosphere a layer of ozone (O3, made of three oxygen atoms) absorbs the Sun's harmful ultraviolet rays, protecting all life from skin cancer and crop damage. Man-made chemicals called CFCs drift up, are broken by UV light, and release chlorine that destroys ozone, thinning the layer. Closer to the ground, our own activities cause pollution: smoke and gases foul the air, sewage and chemicals spoil water, and pesticides and waste damage soil. Protecting these resources means cutting pollution and using them wisely.