Notifications

Log in to see your notifications.

Earth Systems

14 min read

The Earth as a set of systems

The Earth is a system in which four connected spheres interact: the lithosphere (rocks and soil), the hydrosphere (water), the atmosphere (air) and the biosphere (living things). Energy from the Sun drives the system.

Hydrosphere and the water cycle

The hydrosphere includes all the water on the Earth: oceans (97%), ice caps and glaciers, groundwater, lakes, rivers and water vapour. Water moves continuously in the water cycle.

The water cycleHeat from the sun makes water evaporate from the sea, lakes and rivers, and plants release water vapour by transpiration. The vapour rises, cools and condenses into clouds. Water falls as rain, snow or hail, runs over the land into rivers or soaks into the ground, and flows back to the sea.evaporationcondensationprecipitationrunoff to riversinfiltrationtranspirationsea, lakes, rivers
Percentage of all water. Fresh water is only about 3% of the total.

Atmosphere

The atmosphere is a layer of gases held by gravity. Dry air is 78% nitrogen, 21% oxygen and about 1% argon, with a small amount of carbon dioxide (0.04%). The greenhouse effect, in which gases such as carbon dioxide and methane trap heat, keeps the Earth warm enough for life; human activity is strengthening it, causing global warming.

Layers of the atmosphereFive layers, from the ground up. The troposphere holds the weather and most of the air; temperature falls with height. The stratosphere contains the ozone layer, which absorbs ultraviolet light. The mesosphere is the coldest; the thermosphere is very hot and has the auroras; the exosphere fades into space.Exosphereabove 700 km: fades into spaceThermosphere85–700 km: auroras, satellitesMesosphere50–85 km: meteors burn up, coldest layerStratosphere12–50 km: ozone layer, aeroplanesTroposphere0–12 km: weather, clouds, life
The greenhouse effectSunlight passes through the atmosphere and warms the Earth’s surface. The surface gives out heat as infrared radiation. Greenhouse gases such as carbon dioxide, methane and water vapour absorb some of this heat and send part of it back to the surface, which keeps the Earth warm. More greenhouse gas traps more heat and raises the temperature.atmosphere with greenhouse gases (CO₂, CH₄, H₂O)Earth’s surfacesunlight ininfrared (heat) outheat sent back

Biosphere

The biosphere is the part of the Earth where life exists: the soil, water and lower atmosphere. Living things depend on each other and on the other spheres. Matter such as carbon cycles through them.

The carbon cycleCarbon dioxide in the air is taken in by plants for photosynthesis. Plants and animals release it by respiration, dead matter releases it when it decays, and burning fuels releases it. Animals get carbon by eating plants and the dead remains of both return to the soil.Carbon dioxide in the airPlantsAnimalsDead matterFuels burntphotosynthesisrespirationrespirationdecayeatendeathburning
Try itA simple water budget

Water arrives as rainfall and leaves by evaporation (and transpiration) and runoff. Choose the figures for a region for a year.

Check yourself Which layer of the atmosphere contains the weather?
Check yourself The sphere that includes all living things is the
Check yourself Most of the Earth’s water is in the

Key terms

Hydrosphere
All the water on the Earth.
Atmosphere
The envelope of gases round the Earth.
Biosphere
The zone of life.
Greenhouse effect
The trapping of heat by gases in the atmosphere.

Summary

  • The lithosphere, hydrosphere, atmosphere and biosphere interact.
  • Water moves in the water cycle.
  • Air is 78% nitrogen and 21% oxygen; the troposphere contains the weather.
  • Human activities affect all the spheres.
Internal Structure of the Earth Map Reading and Interpretation