Earth's spheres
The region near Earth can be divided up into four interconnected parts, or ‘spheres’, which together make up a complete system. The names of the four spheres are derived from the Greek words for stone, vapour, water, and life:
litho
atmo
hydro
bio
Lithosphere
The lithosphere comprises all of the rocks on Earth, and therefore includes the crust and the upper part of the mantle. The lithosphere reaches to where the rocks of the mantle start to demonstrate plasticity, i.e. become viscous and fluid-like. The lithosphere is broken up into seven major plates and numerous minor plates which move slowly, giving rise to earthquakes, volcanoes, mountains, and ocean trenches.
Atmosphere
The atmosphere is a 500 km thick blanket of gases surrounding Earth. It insulates Earth from extreme temperatures, and recycles water and other chemicals. It also works with electrical and magnetic forces to provide a moderate climate.
Hydrosphere
The hydrosphere is all the water on or near Earth’s surface. As such, it not only includes all rivers, lakes, and oceans, but also underground aquifers and the moisture in the air. 97 % of Earth’s water is found in the ocean, with 2 % frozen in ice caps and glaciers and 1 % on or under land or in the atmosphere.
Biosphere
The biosphere comprises all living things. On land, the range of most life is from 3 m below ground to 30 m above it. In the ocean most life is found in the top 200 m. However, life can be found well outside these ranges.