INTRODUCTION

The elements that make up the living and nonliving components of ecosystems are recycled. Organisms capture material, perform chemical transformations, and release materials back into circulation. In the accompanying animation, we focus on the carbon cycle, describing the flow of this element in its various chemical forms as it moves through organisms and the physical environment—the atmosphere, oceans, fresh waters, and land.

CONCLUSION

Life greatly influences the cycling of matter on Earth.

Carbon, in particular, cycles in vast amounts through living organisms. In the form of CO₂, carbon enters plants and other primary producers during photosynthesis. These organisms convert CO₂ into organic compounds that the rest of life on Earth can take in. As carbon is incorporated into the body of an organism, or as it passes from one organism to another, it is chemically transformed until, finally, it is released back into the atmosphere in the form of CO₂.

Recently, the carbon cycle has become out of balance. More carbon is now released into the atmosphere than is returned back to living organisms or to that vast carbon sink, the ocean. The primary culprit is humankind. We burn fossil fuels—organic carbon repositories that had long ago been removed from the carbon cycle—and thereby release large amounts of extra carbon dioxide into the atmosphere. The sudden release of carbon dioxide has not been compensated by an equal removal of carbon dioxide from the atmosphere. One consequence is that the excess atmospheric CO₂ increases the atmosphere's heat-insulating capacity and contributes to global warming.

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