Earth’s Systems and Water Distribution
Four connected systems
Earth’s materials are grouped into four systems: the geosphere (rock, soil, and landforms), the hydrosphere (all water - oceans, rivers, lakes, groundwater, ice, and water vapor), the atmosphere (the gases around Earth), and the biosphere (all living things). These systems constantly exchange matter and energy.
Interactions to recognize
Rain falling on a hillside is an atmosphere–hydrosphere interaction. That rain washing soil into a river adds the geosphere. Plant roots cracking rock, or trees holding soil in place, connect the biosphere and geosphere. Wind blowing sand links the atmosphere and geosphere. Evaporation from the ocean that later falls as rain far inland links the hydrosphere and atmosphere.
How water is distributed
Most of Earth’s water - about 97 percent - is salt water in the oceans and is not directly usable by most living things. Only a small share is fresh water, and most of that is frozen in ice sheets and glaciers. Very little fresh water is liquid in lakes, rivers, and underground. Questions with pie charts or bar graphs test whether you read the categories carefully.
Traps to watch for
- “Most fresh water is in rivers and lakes.” No - most fresh water is frozen.
- Treating the four systems as separate. When a question asks for an interaction, name at least two systems.
- Assuming all water is drinkable.
Rule of thumb
When reading a graph of Earth’s water, first separate salt from fresh, then separate frozen from liquid.