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Models of
Geosystems

Discover how Earth materials cycle through interconnected geosystems: the atmosphere, hydrosphere, geosphere, and biosphere.

Earth & Space Science

What Is a Geosystem?

A geosystem is any one of Earth's major interconnected spheres. Each sphere contains different materials: air, water, rock, or living things. Together, they form a single planet-wide system where matter and energy constantly move from one sphere to another.

Earth's Four Spheres

Atmosphere
The layer of gases surrounding Earth: nitrogen, oxygen, carbon dioxide, water vapor.
Hydrosphere
All water on Earth: oceans, rivers, lakes, glaciers, and groundwater.
Geosphere
Solid Earth: rocks, minerals, soil, the mantle, and the core.
Biosphere
All living organisms: plants, animals, fungi, bacteria, and their ecosystems.

Why Do We Build Models?

Scientists build models to represent complex systems in simpler ways. A model of geosystems shows how materials like water, carbon, and nitrogen move between spheres. Models help us:

1
Visualize invisible processes: We can't see carbon atoms moving, but a model traces their path.
2
Make predictions: If more \( \text{CO}_2 \) enters the atmosphere, what happens to ocean temperature?
3
Communicate ideas: A diagram of the water cycle is easier to share than a 10-page description.

The Core Principle

EARTH SYSTEM Atmosphere Hydrosphere Geosphere Biosphere

Cycles Are Connections

Three major biogeochemical cycles show how materials move between geosystems. Each cycle traces a single type of matter through all four spheres.

Water Cycle
\( \text{H}_2\text{O} \) moves via evaporation, condensation, precipitation, and runoff across all four spheres.
Carbon Cycle
\( \text{CO}_2 \) moves through photosynthesis, respiration, combustion, and ocean absorption.
Rock Cycle
Rock transforms between igneous, sedimentary, and metamorphic forms through heat, pressure, and weathering.

Open vs Closed Systems

Open System Closed System
Energy exchange Yes Yes
Matter exchange Yes No
Earth example A single lake (water flows in/out) Earth as a whole (almost no matter enters or leaves)
Model implication Must track inputs and outputs All matter must be accounted for within the system

How to Build a Model

1
Choose your material: Pick a substance to trace: water, carbon, nitrogen, or a specific rock type.
2
Identify the spheres: List which geosystems the material passes through during its cycle.
3
Draw reservoirs: Show where the material is stored (ocean, atmosphere, soil, organisms) as labeled boxes.
4
Add arrows for processes: Connect reservoirs with labeled arrows showing how material moves (evaporation, weathering, photosynthesis).
5
Label the sphere for each reservoir: Color-code or tag each box with its geosystem to show the connections.

Example: The Water Cycle

Atmosphere Water vapor, clouds Ocean Hydrosphere Soil & Rock Geosphere Plants Biosphere Precipitation Evaporation Rain Runoff Absorption Transpiration

Example: The Carbon Cycle

Atmosphere
\( \text{CO}_2 \) gas
Living Things Biosphere Ocean Hydrosphere Fossil Fuels & Rock Geosphere Photosynthesis Respiration Absorption Release Decomposition Combustion

Example: The Rock Cycle

Igneous Sedimentary Metamorphic Magma Weathering & Erosion Heat & Pressure Melting Cooling Heat & Pressure Melting

Sphere Interactions

Every geosystem event involves at least two spheres. Here are some examples of how interactions work:

Volcano Erupts
Geosphere releases lava and ash. Atmosphere fills with gas and particles. Biosphere organisms are displaced.
River Floods
Hydrosphere overflows. Geosphere soil erodes. Biosphere habitats are disrupted. Atmosphere humidity increases.
Forest Fire
Biosphere trees burn. Atmosphere receives \( \text{CO}_2 \). Geosphere soil is exposed. Hydrosphere runoff increases.

Energy Drives the Cycles

Two primary energy sources power all geosystem cycles:

Solar Energy
Drives the water cycle (evaporation), weather, and photosynthesis. Powers surface processes in the carbon and nitrogen cycles.
Earth's Internal Heat
Drives the rock cycle (melting, metamorphism), plate tectonics, and volcanic activity. Powered by radioactive decay deep inside Earth.

Reservoirs and Fluxes

Two key vocabulary terms help scientists describe what happens inside a cycle:

Reservoir
A place where material is stored for a period of time. Examples: the ocean (stores water), limestone (stores carbon), the atmosphere (stores nitrogen).
Flux
The rate of movement of material between reservoirs. A higher flux means faster cycling. Example: evaporation rate is a flux in the water cycle.

Common Mistakes

✕ Thinking Cycles Are Linear
Materials don't follow a single path. Water can go from the ocean to the atmosphere and back without touching soil. Cycles have many branches.
✕ Forgetting Energy Sources
A model that shows matter moving but doesn't explain what drives the movement is incomplete. Always include the energy source.
✕ Mixing Up Spheres
Soil is geosphere, not biosphere. The ocean floor is geosphere. Water in a lake is hydrosphere. Label carefully.

Summary of Major Cycles

Cycle Material Key Processes Primary Energy
Water Cycle \( \text{H}_2\text{O} \) Evaporation, condensation, precipitation, runoff Solar
Carbon Cycle \( \text{CO}_2 \) / \( \text{C} \) Photosynthesis, respiration, combustion, decomposition Solar + Internal
Rock Cycle Minerals & Rock Weathering, melting, cooling, compaction Internal + Solar
Nitrogen Cycle \( \text{N}_2 \) Fixation, nitrification, denitrification Solar (biosphere-driven)

Question 1 of 5

A scientist wants to model how carbon moves from the atmosphere into the ocean. Which pair of terms best describes the atmosphere and the ocean in this model?

Question 2 of 5

During the water cycle, a plant absorbs water from the soil and releases water vapor into the air. Which two spheres are directly interacting when the plant releases water vapor?

Question 3 of 5

Earth is best described as a closed system for matter because:

Question 4 of 5

In a model of the rock cycle, which process moves material from metamorphic rock to magma?

Question 5 of 5

A student's geosystem model shows boxes for the ocean, atmosphere, and soil, connected by arrows. The model is missing something important. What should the student add to make the model more complete?