AI Tutor
Every single carbon atom in your DNA has been on Earth for over 4.5 billion years β€” it might have once been inside a swimming plesiosaur, locked inside a deep limestone cave, or floating in the air over a Cretaceous fern forest.
In chemistry, a reservoir is a storage compartment where an element accumulates, and a flux is the rate at which that element moves from one reservoir to another over time.

The Four Earth Reservoirs

Earth organizes carbon across four main reservoirs: the atmosphere (gases), biosphere (living and dead biomass), hydrosphere (dissolved ocean carbon), and geosphere (rocks, sediments, and fossil fuels).
How do chemical reactions actively pump carbon back and forth between the atmospheric gas and living organisms every single day?

Atmosphere and Biosphere: The Fast Cycle

Plants and cyanobacteria remove gaseous carbon dioxide (extCO2 ext{CO}_2) from the atmosphere during photosynthesis, converting light energy and water into solid glucose (extC6extH12extO6 ext{C}_6 ext{H}_{12} ext{O}_6).
Living organisms then perform cellular respiration, breaking down those carbohydrates with oxygen to extract energy while returning extCO2 ext{CO}_2 gas straight back into the atmosphere.
What happens when atmospheric extCO2 ext{CO}_2 encounters the vast surface waters of the ocean?

Atmosphere and Hydrosphere: Ocean Exchange

At the ocean surface, gaseous extCO2 ext{CO}_2 dissolves directly into seawater and reacts with water molecules to produce carbonic acid (extH2extCO3 ext{H}_2 ext{CO}_3).