UNIT 2: REPRESENTING THE EARTH

2.1 The spheres of the Earth

1. The atmosphere

2. The biosphere
With the prefix 'life,' this means that Earth's biosphere is composed of all the living organisms on the planet. This includes plants, animals, bacteria, fungi and single-celled organisms found on Earth. Most of this life exists no deeper than about 10 feet into the ground or about 600 feet above it.

3. The geosphere

Since 'geo' means 'ground,' the geosphere describes all the rocks, minerals and ground that are found on and in Earth. This includes all mountains on the surface, as well as all the liquid rock in the mantle below us and the minerals and metals of the outer and inner cores. The continents, the ocean floor, the rocks on the surface, and the sand in the deserts are considered part of the geosphere. 

4. The hydrosphere

Knowing that 'hydro' means 'water,' you may have guessed that the hydrosphere is made up of all the water on Earth. This includes all rivers, lakes, streams, oceans, groundwater, polar ice caps, glaciers and moisture in the air (like rain and snow). The hydrosphere is found on the surface of Earth, but also extends down several miles below, as well as several miles up into the atmosphere.

Most of Earth's water is salty as in the oceans - about 97%. Two-thirds of the remaining 3% is frozen in glaciers and polar ice caps. Only 1% of the hydrosphere is liquid freshwater, and even most of this exists as groundwater down in the soil.