Carbon Cycle and Oxygen Cycle

There are several elements necessary for the survival of life on Earth. The elements occur naturally and are constantly recycled through Earth’s major spheres: the hydrosphere, atmosphere, biosphere, and geosphere. There are four major biochemical cycles. The oxygen cycle is continuously moving oxygen among the atmosphere, water, plants, animals, and the Earth’s crust. Therefore oxygen is not only present in the atmosphere; but it also available as dissolved oxygen in water to support aquatic organisms. Aquatic animals need oxygen to survive as much as humans need oxygen to breathe. Photosynthesis is the major process that releases oxygen into the environment. Green plants take in carbon dioxide from the atmosphere and water from the environment along with energy from the sun. Then the green plants release oxygen into the atmosphere.

Oxygen can exist alone in the atmosphere as a diatomic molecule or it can combine with another element such as hydrogen to make H2O, a water molecule. About 70% of the Earth is covered with water. Compounds such as nuclei acids, proteins, cellulose, and carbohydrates also contain the element oxygen.   With the exception of cellulose, these compounds can be found in both plants and animals. Over half of Earth’s lithosphere contains minerals combined with oxygen. Recall that the mantle makes up about 70% of the Earth’s mass. Oxygen, silicon, aluminum, and iron can be found within the mantle.   Almost all of our planet’s rocks contain compounds that consist of oxygen. Hematite is a metallic mineral from the iron oxides mineral group. It is used to make steel and jewelry. Hematite can be found in all three types of rocks. Sedimentary rocks such as limestone, sandstone, and shale also contain oxygen.

The carbon cycle and the oxygen cycle are interconnected.  Nearly all living things need oxygen.  Just about all living and non-living things are made up of carbon. The most common reservoirs that transport carbon and oxygen as they cycle are the atmosphere, marine, terrestrial, and lithosphere.  The greatest amount of carbon is stored in the lithosphere. The shells or skeletons of marine animals are made of calcite. When marine animals die, their shells or skeletons settle to the ocean floor and over time become a sedimentary rock called limestone. If this rock reaches the Earth’s surface and undergoes chemical weathering, carbon dioxide is released into the atmosphere.

Respiration, also called cellular respiration, is one of two major processes that also release carbon into the environment. Animals, which include humans, take in the glucose and oxygen produced by photosynthesis. Through cellular respiration, animals then release carbon dioxide and water.

Combustion is the other major process by which carbon is released into the environment.  Natural combustion includes volcanic eruptions.  Humans are responsible for pollution problems due to combustion from cars, factories, and the burning of fossil fuels.  A fossil fuel is any combustible organic matter derived from the decomposed remains of plants and animals that was created by the extremely high amounts of heat and pressure within the Earth.   Petroleum, oil, natural gas, peat, and coal are examples of fossil fuels.  They are used to produce energy.

Decomposition is another process by which carbon dioxide is returned to the atmosphere.  Fungi and bacteria are called decomposers.  Decomposers break down, remove, and recycle carbon from the rotting remains of dead plants and animals.  Therefore carbon can be found in the atmosphere, oceans, alive as well as deceased organisms, and rocks.


Click the question to reveal the answer.

What is the equation for photosynthesis?

6CO2 + 6H2O + Energy arrow C6H12O6 + 6O2


What is the equation for cellular respiration?

C6H12O6 + 6O2 arrow 6CO2 + 6H2O + Energy


Where do plants get their energy to uptake gaseous or dissolved carbon dioxide?



What happens to the sediments that are buried at the bottom of the ocean?

They become sedimentary rocks.


Volcanic eruptions release which type of gas into the atmosphere?

Carbon Dioxide


This process exchanges carbon dioxide between the ocean and the atmosphere.