Earth's System and Carbon Cycle

Overview

This lecture explains the four main components ("spheres") of Earth's system and describes how matter, especially carbon, cycles between them.

The Earth's system consists of interconnected spheres: atmosphere, hydrosphere, geosphere, and biosphere.
Matter flows between these spheres, acting as reservoirs for different materials.
The rate at which material enters and exits a sphere is called flux.
Reservoir sizes remain constant if inflow and outflow are balanced.

Water cycles between the ocean (reservoir) and other spheres via processes like rainfall, river flow, and evaporation.
Imbalances, such as ice sheets trapping water, can change sea levels.
Recent glacier melt increases ocean water volume and raises global sea levels.

Carbon moves between Earth's spheres: atmosphere, hydrosphere, geosphere, and biosphere.
The atmosphere contains a small but climatically significant amount of carbon dioxide (CO₂).
CO₂ enters the atmosphere through decomposition and forest fires, and increases due to fossil fuel use.
Oceans (hydrosphere) exchange CO₂ with the atmosphere; carbon forms carbonate minerals and enters shells of marine organisms.
When these organisms die, their remains can become limestone in the geosphere.
The geosphere stores the most carbon, mainly as rocks and fossil fuels.
The biosphere includes all living things; most of its carbon is in plants and soil.
Plants absorb atmospheric CO₂ via photosynthesis; soils store decaying plant material.

Human activities, especially fossil fuel combustion, release ~9 gigatons of carbon per year from the geosphere.
Some excess carbon is absorbed by oceans and the biosphere, but about 4 gigatons remain in the atmosphere.
Increased atmospheric carbon is tracked by the Keeling Curve and contributes to climate change.

Changes in one sphere, such as increased atmospheric carbon, cause changes in the others.
The geosphere exchanges carbon slowly, while the atmosphere has fast fluxes.
To halt atmospheric carbon increase, we must reduce carbon emissions or enhance uptake in other spheres.

Sphere — a distinct component of Earth's system (atmosphere, hydrosphere, geosphere, biosphere).
Carbon Cycle — movement of carbon among Earth’s spheres.
Reservoir — a storage location for matter within a sphere.
Flux — the rate of movement of matter between reservoirs.
Keeling Curve — a graph showing the rising concentration of CO₂ in the atmosphere.
Photosynthesis — process by which plants absorb CO₂ and convert it into carbohydrates.

Review the three learning objectives provided in class and assess your confidence in completing them.
Reflect on how changes in one Earth system component affect the others.