The Four Spheres of the Earth

Learn about the Atmosphere, Biosphere, Hydrosphere, Lithosphere

Planet Earth Viewed from the International Space Station
Planet Earth Viewed from the International Space Station. ESA / Getty Images News / Getting Images

The area near the surface of the earth can be divided up into four inter-connected "geo-spheres": the lithosphere, hydrosphere, biosphere, and atmosphere. Scientists can classify life and material on or near the surface of the earth to be in any of these four spheres.

The names of the four spheres are derived from the Greek words for stone (litho), air (atmo), water (hydro), and life (bio).

Lithosphere

The lithosphere is the solid, rocky crust covering entire planet.

This crust is inorganic and is composed of minerals. It covers the entire surface of the earth from the top of Mount Everest to the bottom of the Mariana Trench.

The actual thickness of the lithosphere varies considerable, and can range from roughly 40 km to 280 km. The lithosphere ends at the point when the minerals in the earths crust begin to demonstrate viscous and fluid behaviors. The exact depth at which this happens depends on the chemical composition of the earth, and the heat and pressure acting upon the material.

Hydrosphere

The hydrosphere is composed of all of the water on or near the earth. This includes the oceans, rivers, lakes, and even the moisture in the atmosphere. Over ninety-seven percent of the earth's water is in the oceans. The remaining two-and-a-half percent is fresh water; over two-thirds of the fresh water on the planet is solid and exists in ice sheets.

It's interesting to note that even though earth is often described as a "water planet," and the majority of the surface of earth is covered by water, water accounts for a mere 0.023% of the earth's total mass.

Biosphere

The biosphere is composed of all living organisms. Plants, animals, and one-celled organisms are all part of the biosphere. Most of the planet's life is found from three meters below the ground to thirty meters above it and in the top 200 meters of the oceans and seas. But life can live far outside of these ranges: some birds are known to fly 8 kilometers up, and fish have been found over 8 kilometers beneath the ocean surface.

Microorganisms are known to survive well beyond these ranges. The biosphere is made up of biomes.

The term "biosphere" is also used to describe a self contained ecosystem such as the biospheres that are being tested for the future colonization of Mars.

Atmosphere

The atmosphere is the body of air which surrounds our planet. Most of our atmosphere is located close to the earth's surface where it is most dense. The air of our planet is 79% nitrogen and just under 21% oxygen; the small amount remaining is composed of carbon dioxide and other gasses.

A Final Note

All four spheres can be and often are present in a single location. For example, a piece of soil will of course have mineral material from the lithosphere. Additionally, there will be elements of the hydrosphere present as moisture within the soil, the biosphere as insects and plants, and even the atmosphere as pockets of air between soil pieces.