"Hydrosphere" is searched about 36,000 times a month in the United States, and "Earth's spheres" another 3,000, because the four-sphere model is the organising idea of Grade 5 Earth science (NGSS 5-ESS2-1 asks for a model of how the geosphere, biosphere, hydrosphere and atmosphere interact) and reappears through middle school, KS3 and Class 7 Geography. This page says what each sphere is and contains, gives 20 interactions, then goes into the hydrosphere properly with the US Geological Survey's figures for where the water is, describes the water cycle as the spheres exchanging water, and gives a printable chart with practice.
Download the four spheres chart with practice (PDF) (A4, the four spheres, the interactions table and the water figures on page 1, the water cycle and the practice set with answers on page 2, free).
The four spheres
| Sphere | What it is | What it contains | Studied by |
|---|---|---|---|
| Geosphere (lithosphere) | the solid Earth | crust, mantle, core; rocks, minerals, soil, sediment, mountains, the sea floor, volcanoes | geology |
| Hydrosphere | all the water | oceans, seas, lakes, rivers, groundwater, soil moisture, water vapour and clouds, ice and snow, water in living things | hydrology, oceanography |
| Atmosphere | the layer of gases | nitrogen 78%, oxygen 21%, argon 0.9%, carbon dioxide 0.04%, water vapour; the troposphere (weather), stratosphere (ozone), mesosphere, thermosphere, exosphere | meteorology, atmospheric science |
| Biosphere | all living things, where they live | every organism from bacteria to whales, in the soil, water and air; spans the lower atmosphere to the deep ocean and a few kilometres into rock | biology, ecology |
| Cryosphere (often separated) | the frozen water | ice sheets (Antarctica, Greenland), glaciers, sea ice, snow, permafrost | glaciology |
The names come from Greek: geo earth, hydro water, atmos vapour, bios life, kryos cold; sphaira a ball. The spheres are not layers one on top of another; they interpenetrate. Soil is geosphere, hydrosphere (moisture), atmosphere (air in the pores) and biosphere (roots, worms, bacteria) in one handful.
How the spheres interact: 20 examples
| Event | Spheres involved | What crosses between them |
|---|---|---|
| Volcano erupts | geo → atmo, hydro, bio | ash and gases into the air; lava into the sea; habitats buried, soil later enriched |
| Rain falls on a hillside | hydro → geo, bio | water erodes soil and dissolves minerals; plants take it up |
| Plant photosynthesises | bio ↔ atmo, hydro | takes carbon dioxide and water, gives oxygen |
| Animals breathe | bio ↔ atmo | take oxygen, give carbon dioxide |
| Tree roots split a rock | bio → geo | biological weathering |
| River carries sediment to the sea | hydro → geo | erosion and deposition build a delta |
| Hurricane | hydro, atmo → geo, bio | warm ocean feeds the storm, which floods land and wrecks habitats |
| Ocean absorbs carbon dioxide | atmo → hydro → bio | dissolves, forms carbonic acid, affects shell-building animals |
| Glacier carves a valley | cryo → geo | U-shaped valleys, moraines |
| Ice melts | cryo → hydro | sea level rises; fresh water into the ocean |
| Forest fire | bio → atmo, geo | smoke and carbon dioxide into the air; ash onto soil |
| Earthquake under the sea | geo → hydro | a tsunami |
| Evaporation from the ocean | hydro → atmo | water vapour, later clouds and rain |
| Wind erodes a desert | atmo → geo | sand dunes, dust storms |
| Lightning starts a fire; fixes nitrogen | atmo → bio, geo | nitrogen compounds into soil |
| Farming | bio (humans) → geo, hydro, atmo | ploughing, irrigation, fertiliser run-off, methane |
| Burning fossil fuels | geo (coal, oil) → atmo → hydro, bio | carbon dioxide, warming, acidification |
| Coral reef builds | bio → geo | limestone from living things |
| Salt marsh traps mud | bio, hydro → geo | new land |
| A landslide dams a river | geo → hydro → bio | a new lake, drowned forest |
The NGSS Grade 5 question is "describe one interaction": pick a row, name the two spheres, say what moved. The middle-school version asks for a chain: ocean → atmosphere → land → ocean.
The hydrosphere in detail: where the water is
The US Geological Survey's Water Science School gives these figures (from Shiklomanov's estimate; the total is about 1,386 million cubic kilometres):
| Store | Share of all water | Share of fresh water |
|---|---|---|
| Oceans and seas (saline) | 96.5% | |
| Saline groundwater and lakes | about 1% | |
| All fresh water | 2.5% | 100% |
| Glaciers, ice caps, permanent snow | 1.74% | 68.7% |
| Groundwater (fresh) | 0.76% | 30.1% |
| Ground ice and permafrost | 0.022% | 0.86% |
| Lakes (fresh) | 0.007% | 0.26% |
| Soil moisture | 0.001% | 0.05% |
| Atmosphere | 0.001% | 0.04% |
| Swamps and wetlands | 0.0008% | 0.03% |
| Rivers | 0.0002% | 0.006% |
| Living things | 0.0001% | 0.003% |
Three facts to take from the table. Almost all water is salt: 97.5 percent of it. Almost all fresh water is ice or underground: 98.8 percent of the fresh water is in glaciers, ice caps and groundwater. Rivers and lakes, where people get most of their water, hold about a quarter of one percent of the fresh water, which is why the hydrosphere is renewable only as fast as the water cycle refills them. If all Earth's water were a sphere it would be about 1,385 km across (the USGS illustration); the fresh liquid water alone would be a sphere about 56 km across.
The ocean averages 3.7 km deep and holds 1.335 billion km³; the Antarctic ice sheet holds about 60 percent of the world's fresh water and would raise sea level about 58 m if it all melted (the Greenland sheet about 7 m).
The water cycle: the spheres exchanging water
The water cycle is the hydrosphere moving through the other three spheres, driven by the Sun's energy and gravity:
- Evaporation from oceans, lakes and soil, and transpiration from plants (biosphere), put water vapour into the atmosphere.
- Condensation forms clouds; precipitation (rain, snow, hail) returns water to the surface.
- On land it becomes surface run-off into rivers and lakes (geosphere channels), infiltrates to become soil moisture and groundwater, is stored as snow and ice (cryosphere), or is taken up by living things (biosphere).
- Rivers and groundwater return it to the ocean; ice melts; the cycle continues. A water molecule spends about nine days in the atmosphere, weeks to months in a river, decades to centuries in a lake or glacier, and thousands of years in the deep ocean or deep groundwater.
Every arrow in the water cycle diagram is a sphere interaction, which is how the two topics are examined together in Grade 5 and KS3.
Where it sits in each curriculum
| Curriculum | When | What is expected |
|---|---|---|
| US (NGSS) | Grade 5 (5-ESS2-1: develop a model using an example to describe ways the geosphere, biosphere, hydrosphere and atmosphere interact; 5-ESS2-2: graph the amounts of salt and fresh water), middle school (MS-ESS2-4: the water cycle driven by the Sun and gravity) | the four spheres, one worked interaction, the water figures |
| England | KS2 Year 4 (states of matter, the water cycle), KS3 (Earth and atmosphere: the rock cycle, the carbon cycle, the composition of the atmosphere), GCSE Geography (the water cycle, stores and flows) | the spheres as a framework in geography |
| Australia | Year 7 (water as a resource; the water cycle), Year 9 (AC9S9U02: global systems, including the carbon cycle, rely on interactions between the geosphere, biosphere, hydrosphere and atmosphere) | the four spheres named in Year 9 |
| India (CBSE) | Class 7 Geography (Our Environment: lithosphere, hydrosphere, atmosphere, biosphere), Class 9 Geography (natural vegetation, drainage) | the four domains in Class 7 |
| Canada (Ontario) | Grade 7 (Earth's crust), Grade 8 (water systems: the hydrosphere, glaciers, groundwater) | water systems in Grade 8 |
Practice (answers in the PDF)
- Name the four spheres and give one thing found in each.
- A flood washes topsoil from a field into a river, which carries it to the sea. Which spheres interact, and what moves between them?
- What percentage of Earth's water is fresh? Where is most of the fresh water?
- Explain why rivers are so important to people even though they hold a tiny fraction of the water.
- Describe two ways the biosphere changes the atmosphere.
- Is a cloud part of the hydrosphere or the atmosphere? Explain.
Download the chart and the practice set (PDF)
Where to get help
A 1-on-1 online science class with a tutor who teaches NGSS Grade 5 to 8 Earth science, KS2 and KS3 science and geography, the Australian Years 7 to 9 and CBSE Class 7 to 9 every week: the spheres taught through real events (a volcano, a flood, a drought), with the water figures drawn as a bar chart so the proportions are seen, not read. The Earth science page lists the courses; the free 30-minute first class is a real lesson on this week's topic. Related pages: weathering and erosion and types of ecosystems.
Questions parents ask
1What is the hydrosphere?
2What are Earth's four spheres?
3How do the spheres interact?
4Where is most of Earth's fresh water?
5What is the difference between the geosphere and the lithosphere?
See how we teach this, 1-on-1 online →
Shobha
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Teaching maths, science and English to children online since 2018. 500+ students, 20+ tutors, families in nine countries.