This drawing shows the water cycle.
Click on image for full size
Carbonate is a name for rocks and minerals which contain a molecule made of both carbon and oxygen known as CO32-. (CO32- is also known as the molecule carbonate).
Limestone is an example of a calcium carbonate, CaCO3, which means a combination of calcium (Ca2+) and carbonate (CO32-). Other examples of carbonates include calcite, dolomite, and marble.
Limestone is a fine-grained calcium carbonate and dissolves easily in rainwater, especially rainwater which is loaded with carbon dioxide in the form of carbonic acid. The more carbon dioxide in the rain, the more easiy limestone and marble dissolve.
As a result of human activity such as the burning of fossil fuels which inject more carbon dioxide into the air, limestone more readily dissolves. This process also helps to remove carbon dioxide from the atmosphere. Another way of looking at that same process is that a way to remove excess carbon dioxide from the atmosphere is by the dissolution of carbonates such as limestone and marble. The removal of carbon from the atmosphere and recycling in the ocean is part of the carbon cycle.
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