Most of the carbon dioxide that was once part of earth's atmosphere can now be found in a. fossil fuels b. the oceans c. carbonate rocks d. living things, such as plants

Carbon is also found in the atmosphere where it's a part of carbon dioxide gas emitted when fossil fuels are burned and when living organisms breathe. It's in organic matter in the soil, and it's in rocks. But far and away the most carbon on Earth is stored in a surprising place: the ocean

source: https://science.howstuffworks.com/environmental/green-science/earth-carbon-stored.htm

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