Carbon is cycled through the hydrosphere and geosphere through biological, chemical, geological, and human activity.
Let's take a forest, for example. These autotrophs take in carbon dioxide (CO2) during photosynthesis. They then release oxygen to the environment and give organisms that perform cellular respiration enough oxygen. Then, the organisms that perform cellular respiration breathe out CO2 that can be used by autotrophs. The consumers can also eat the autotrophs and release CO2 as they breathe out.
When rainwater falls from clouds in the atmosphere, CO2 is dissolved into the drops of rain. The rain (some of it) then goes into oceans and is dissolved into the ocean with the CO2. Then, it comes back from the water and floats up into the atmosphere again.
Rocks at the bottom of the ocean are naturally turned into carbonated rocks, and it releases CO2 through volcanoes. Also, it can convert organic matter into fossil fuels.
Humans take fossil fuels from the Earth and use them as a source of fuel. This naturally releases the carbon dioxide in them, as they are converted into carbon over a very long period of time. Also, humans sometimes burn forests. The fire releases carbon dioxide into the atmosphere.
The same processes that occur geologically and biologically occur in the ocean. Green algae take in CO2 and use it the same way.
