Biogeochemical Cycles

BIOGEOCHEMICAL CYCLES describe how chemical elements MOVE through Earth's living things, atmosphere, water, and rocks. The big four: CARBON, NITROGEN, WATER, and PHOSPHORUS cycles. These elements are the building blocks of life and they don't get used up — they just move and transform. The same carbon atom in your body today could have been in a dinosaur, a tree, the ocean, the air, billions of times.

Quick tour. CARBON: atmosphere (CO₂) ↔ plants (photosynthesis) ↔ animals (respiration) ↔ decomposition ↔ soil/fossil fuels. Burning fossil fuels rapidly releases stored carbon. NITROGEN: makes up 78% of atmosphere as N₂. Bacteria "fix" it into usable forms. Plants absorb it. Animals eat plants. Bacteria release it back. Most usable nitrogen comes from bacteria + lightning + fertilizers. WATER: evaporation → clouds → precipitation → runoff → ocean. Powered by the sun. PHOSPHORUS: rocks → soil → plants → animals → decomposition → soil. No atmospheric phase (unlike the others).

Why these cycles matter. Life depends on them. Disruptions cause big problems. Excess CO₂ → climate change. Excess nitrogen runoff (from fertilizers) → algal blooms and dead zones in lakes/oceans. Phosphorus overuse depletes finite mining sources AND pollutes water. Sustainability is largely about respecting these cycles. Modern challenges (climate, water security, food production) all come back to biogeochemistry.

Biogeochemical cycles are the deep plumbing of planet Earth. Every breath, every meal, every drop of water you use is part of these cycles. Understanding them is understanding how the planet works.