All living organisms contain water and elements like carbon and nitrogen. These essential abiotic factors are limited in ecosystems. They must be recycled continuously between the air, water, land, and life forms. The availability of these important resources determines where life can live on our planet.

Ecosystems depend on the constant cycling of these abiotic factors. At times, some of the abiotic factors are in storage. Any location where abiotic factors are stored is called a sink.

Carbon in rocks like limestone and in fossil fuels like coal can be stored for millions of years. Humus in soil, is an important natural sink of carbon. In a tropical rain forest, the carbon in humus cycles quickly. In the tundra, humus may be trapped in permafrost and the carbon does not cycle until it thaws. A tree, like the giant sequoia, can hang onto its carbon for hundreds of years.

Like carbon, nitrogen is essential to all life. Today, our atmosphere contains about 78% nitrogen gas, but most organisms cannot use it in that form. They depend on either lightning or nitrogen-fixing bacteria in the soil to convert nitrogen gas into a form that can be absorbed by the roots of plants. You get your nitrogen as you do your carbon—by eating plants or animals that have eaten plants.

Polar ice, formed from compacted snow, can lock water molecules out of the water cycle for tens of thousands of years. However, when icebergs break off and melt, the water returns to the cycle again.

Nitrogen and Carbon Cycles

Not only to abiotic and biotic factors cycle, but species and populations go through cycles as well. Fossil evidence shows that in the last 540 million years, our planet has experienced several mass extinctions. Extinction occurs when a species, once present on Earth, dies out. A sudden increase in the rate of extinction may be the result of global climate change, increased volcanic activity, or an astronomical impact event. Whatever the reason for past mass extinctions, life on our resilient planet recovered.