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).
Abiotic and Biotic Spheres
The Earth is divided into four interconnected spheres, one that is biotic and three of which are abiotic.
Biotic sphere
The biotic sphere, known as the biosphere, encompasses all living organisms. This includes a vast diversity of life forms, from microscopic bacteria to towering trees, as well as animals such as birds, mammals, and insects. The biosphere relies on the abiotic spheres for survival, drawing on their resources and contributing to the ongoing cycle of matter and energy.
Abiotic spheres
The abiotic spheres—comprising the lithosphere, atmosphere, and hydrosphere—are made up of non-living components. Abiotic factors include elements such as minerals, gases, and water, all of which do not originate from living organisms. These spheres interact with each other and influence the Earth’s processes, shaping the environment in which life exists.
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Hydrosphere – a biotic sphere
Focusing on the hydrosphere, it encompasses all of Earth’s water, which is crucial for life. This sphere includes surface water, such as rivers, lakes, and oceans; groundwater that saturates the soil and rock beneath our feet; ice and snow found in polar regions and mountain peaks; and water vapor present in the atmosphere. Together, these forms of water play a key role in supporting life and regulating the planet’s climate.Related: Water on Earth
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.
Layers of the Atmosphere
The Earth’s atmosphere has five main layers and a sixth layer, the ionosphere, that overlaps the mesosphere, thermosphere, and exosphere. The five vertical layers of the atmosphere are:
- Troposphere
- Stratosphere
- Mesosphere
- Thermosphere
- Exosphere
Troposphere: The Densest Layer in the Atmosophere
The troposphere, the bottommost layer of Earth’s atmosphere, is the densest of the five atmospheric layers and extends from ground level up to about 10 kilometers in altitude. This is the layer where humans live and breathe, as it contains the air we depend on for survival. The troposphere also holds 99% of the water vapor in the atmosphere, making it the primary region where clouds form and weather patterns occur.
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.
Stratosphere: Home to the Earth’s Ozone Layer
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.
Mesosphere: Highest Layer that has Mixed Gases
Above the stratosphere and below the thermosphere 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 (not to be confused with the exosphere which is the highest layer in Earth’s atmosphere).
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.
Thermosphere: Thin Atmosphere
Above the mesosphere lies the thermosphere, one of the highest layers of Earth’s atmosphere.
The thermosphere is characterized by extremely thin air, with gas molecules spread so far apart that they rarely collide. Despite the sparse atmosphere, temperatures in this layer can soar to as high as 4,500 degrees Fahrenheit. This intense heat is primarily due to the absorption of high-energy X-rays and ultraviolet (UV) radiation from the Sun. However, because the gas molecules are so dispersed, there isn’t enough density for this heat to be felt in the same way it would be at lower altitudes—essentially, the air is too thin to effectively transfer this energy.
The thermosphere is also home to many of the satellites that orbit Earth, as well as the International Space Station (ISS). These objects navigate this layer due to the minimal atmospheric drag, which allows them to maintain stable orbits for extended periods. Additionally, the thermosphere plays a critical role in communication, as it is where radio waves transmitted from Earth can travel long distances by bouncing off the ionized particles present in this region.
Exosphere: Highest Layer in the Atmosphere
The exosphere is the outermost layer of Earth’s atmosphere, gradually transitioning into the vacuum of space.
In the exosphere, the atmosphere becomes exceedingly thin, with gas molecules spread out over vast distances. Unlike the denser layers of the atmosphere closer to Earth, the exosphere contains very few particles, primarily lightweight gases such as hydrogen and helium. These particles are so sparse and spread out that they can travel hundreds of kilometers without colliding with one another, essentially moving in near-empty space.
The exosphere is also the region where some satellites orbit, particularly those designed for long-term observations of Earth or communications. The low density of particles in this layer means that there is minimal drag on these satellites, allowing them to maintain their orbits for extended periods with little need for adjustment.
Ionosphere: Overlaps the Mesosphere, Thermosphere, and Exosphere
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.
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)
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.
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.
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.
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.
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
This article was originally written on March 18, 2020 and has since been updated.
