Every plant, every animal, and every living organism on earth is made of materials that have been used and re-used many times. In short, we are all made of recycled parts! Just think, nitrogen atoms in the protein that makes up your hair might have come from an apple you ate weeks ago. That apple acquired nitrogen atoms from the soil the apple tree was planted in, and the nitrogen in the soil was fixed from nitrogen gas in the air.
All the chemical elements (e.g., carbon, nitrogen, oxygen) that make up living cells continuously flow between living things and the nonliving environment through abiotic cycles. The following are the most well-known abiotic cycles:
- The carbon cycle
- The nitrogen cycle
- The water cycle
- The sulfur cycle
- The phosphorus cycle
- The rock cycle
We will focus on two of these cycles— the carbon cycle and the nitrogen cycle. Let's first take a look at the carbon cycle.