What are the Earth System’s Four Spheres?

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Planet Earth is made up of four overlapping subsystems that contain all of world’s land masses, water sources, living organisms, and gases. These four subsystems are known as spheres.

Geographers break down the Earth’s systems into four spheres that make up the world’s air (atmosphere), water (hydrosphere), land (geosphere), and living organisms (biosphere).

The Earth's four systems.  Images: USGS, public domain.
The Earth’s four systems. Images: USGS, public domain.

Three of these spheres are abiotic and one sphere is biotic. Abiotic describes substances that are made from non-living materials. Biotic relates to living things like bacteria, birds, mammals, insects, and plants.

In this breakdown, all of the Earth’s water is included in the hydrosphere. This includes surface water (such as rivers, lakes, and oceans), water in the ground, ice and snow, and water in the atmosphere in the form of water vapor.

Atmosphere

The Earth’s atmosphere is the gaseous layer that envelopes the world. The commons term for the atmosphere is “air”.

The Earth’s atmosphere is held around the planet by the force of gravity.

A view of the atmosphere from Chain of Craters Road in Hawaii Volcanoes National Park in Hawaii.  Photo: USGS, public domain.
A view of the atmosphere from Chain of Craters Road in Hawaii Volcanoes National Park in Hawaii. Photo: USGS, public domain.

The Earth’s atmosphere has five main layers and a sixth layer, the ionosphere, that overlaps the mesosphere, thermosphere, and exosphere.

The bottom layer, which is the layer closest to the Earth, is the most dense of the five layers. This layer is known as the troposphere. This is the layer of the Earth’s atmosphere that humans live and breathe in.

The troposphere starts at ground level and extends to 10 kilometers in altitude.

The troposphere is also the layer where almost all clouds form because 99% of the water in the Earth’s atmosphere is found in this layer.

Clouds over the Green River, Brown's Park National Wildlife Refuge.  Photo: Jason Alexander, USGS. Public domain.
Clouds over the Green River, Brown’s Park National Wildlife Refuge. Photo: Jason Alexander, USGS. Public domain.

This layer mostly contains a mixture of mostly nitrogen (78%), oxygen (21%), and argon (0.9%). In addition, trace gases (carbon dioxide, nitrous oxides, methane, and ozone) account for another tenth of a percent.

Water vapor, dust particles, pollutants, and pollen also can be found in mixed into the atmosphere at this level.

The higher the altitude, the thinner the atmosphere is.

The next layer is the stratosphere. This layer is the layer that contains the Earth’s ozone layer. Unlike the troposphere, the stratosphere has no turbulence. Unlike the air in the troposphere, the air in the stratosphere gets warmer higher up in this layer.

Above the stratosphere is the mesosphere. This layer in the Earth’s atmosphere is the highest layer in which the gases are still mixed up rather than layered. The mesosphere is the layer where meteors entering the Earth’s atmosphere break up. There are enough gases in the mesosphere to create friction which causes the meteors to burn up. We can see those at night as shooting stars.

The atmosphere in the thermosphere is very thin. Temperatures can reach up to 4,500 Fahrenheit due to high-energy X-rays and UV radiation from the Sun. There aren’t enough gas molecules to transfer this heat. Many earth orbiting satellites and the International Space Station are found in this layer.

The uppermost layer of the Earth’s atmosphere is the exosphere. The atmosphere is extremely thin in this layer with gases like hydrogen and helium.

The ionosphere is an active part of the Earth’s atmosphere that overlaps the the mesosphere, thermosphere, and exosphere. Like its name, the ionosphere is the ionized part of the Earth’s atmosphere and is found between 48 km (30 mi) to 965 km (600 mi) altitude. Auroras occur in the ionosphere where high-energy particles from the sun interacting with the atoms in this layer.

An aurora borealis over the Pacific Northwest in the United States. Image: NASA astronaut Scott Kelly taken from the International Space Station, January 20, 2016.

To sum, the five mains layers in the Earth’s atmosphere are:

  • Exosphere: 700 to 10,000 km (440 to 6,200 miles)
  • Thermosphere: 80 to 700 km (50 to 440 miles)
  • Mesosphere: 50 to 80 km (31 to 50 miles)
  • Stratosphere: 12 to 50 km (7 to 31 miles)
  • Troposphere: 0 to 12 km (0 to 7 miles)
The five main layers of the Earth's atmosphere.  Image: NASA, public domain.
The five main layers of the Earth’s atmosphere. Image: NASA, public domain.

Hydrosphere

All of the water on Earth is known collectively as the Earth’s hydrosphere. This is water found in the air, the soil, in glaciers, the oceans, rivers, lakes, and streams of the world.

Water is found in all three states on Earth which are gas, liquid, and solid.

As gas, water is found as water vapor in the atmosphere.

In liquid form water is found in streams, rivers, lakes, ponds, and oceans along with mist in the air and as dew on the surface of the ground.

Water is found in solid form as ice and snow.

An ocean cave on the coast of Capri Island, Italy. Photo: John J. Mosesso, USGS. Public domain.
An ocean cave on the coast of Capri Island, Italy. Photo: John J. Mosesso, USGS. Public domain.

Lithosphere

The lithosphere contains the elements of the Earth crust and part of the upper mantle. This is the hard and rigid outer layer of the Earth. The term is taken from the Greek word lithos meaning “rocky”. This part of the Earth includes soil.

The Earth's lithosphere is made up of the crust and part of the upper mantle.  Image:  Srimadhav adapted from USGS, public domain.
The Earth’s lithosphere is made up of the crust and part of the upper mantle. Image: Srimadhav adapted from USGS, public domain.

Biosphere

The biosphere covers all living organisms on Earth.

There is an estimated 20 million to 100 millions different species in the world organized into the 100 phyla that make up the five kingdoms of life forms.

These organisms can be found in almost all parts of the geosphere. There are organisms in the air, soil, and water on Earth.

Sandhill cranes flock together on a grassy area in Medaryville, Indiana.  Photo: John J. Mosesso, USGS. Public domain.
Sandhill cranes flock together on a grassy area in Medaryville, Indiana. Photo: John J. Mosesso, USGS. Public domain.

Watch: The Earth’s Four Spheres

Earth Divided into Two Major Systems

Some scientists organized of the parts of the Earth can be divided into two main systems. These two systems include all the organic and inorganic matter of the world.

Every living and non-living thing on Earth falls under one of these two main spheres which are the Earth’s geosphere and biosphere.

As with the four system organization, the biosphere represents all of the Earth’s living organisms.

The geosphere is the collective name for the earth’s atmosphere, lithosphere, hydrosphere, and cryosphere. The atmosphere is the space above the Earth’s surface. This includes the air that we all breath. The lithosphere is the solid part of the Earth such as rocks and mountains. The hydrosphere is the liquid water such as the rivers, lakes, and oceans. The cryosphere is the frozen water of the earth and is further broken into four types: glaciers, snow cover, floating ice, and permafrost.

The Earth can be divided into two main systems: the geosphere and the biosphere. Image: USGS, public domain.
The Earth can be divided into two main systems: the geosphere and the biosphere. Image: James A. Tomberlin, USGS, public domain.

References

Ask an Astronomer. (n.d.). Cool Cosmos. https://coolcosmos.ipac.caltech.edu/ask/64-What-is-the-atmosphere-of-Earth-made-of-

Layers of earth’s atmosphere | UCAR center for science education. (n.d.). UCAR Center for Science Education. https://scied.ucar.edu/atmosphere-layers

Inside the Earth [This Dynamic Earth, USGS]. (n.d.). U.S. Geological Survey Publications Warehouse. https://pubs.usgs.gov/gip/dynamic/inside.html

Williams, R. S. (n.d.). The Earth System. USGS. https://pubs.usgs.gov/pp/p1386a/pdf/notes/1-8hydrocycle_508.pdf

World of Change: Global Biosphere. (2009, June 5). NASA Earth Observatory – Home. https://earthobservatory.nasa.gov/world-of-change/Biosphere

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