Exercises: The Carbon Cycle

List the four Earth systems. Then name one place where carbon is stored in each of the geosphere, the hydrosphere, and the atmosphere.

Name the process by which plants and algae take carbon dioxide from the air or water and convert it to sugars, and name the process by which organisms release carbon dioxide back as they break down food for energy.

Coal, oil, and natural gas are called fossil fuels. State what they are made from and what happens to their stored carbon when people burn them.

A marine organism builds a shell of calcium carbonate ($CaCO_3$). After it dies, the shell sinks to the sea floor and is buried. Describe the path of carbon in this example, naming the forms of carbon (for example, dissolved carbon dioxide, carbonate in shells, and carbonate rock) and the Earth systems it moves among. Explain why this path can store carbon for millions of years.

The table shows approximate carbon stored in several reservoirs.

1. a) Which reservoir holds the most carbon?
2. b) How many times more carbon does that reservoir hold than the atmosphere? Round to the nearest whole number.
3. c) Burning fossil fuels moves carbon from one reservoir to another. Identify the direction of the transfer and explain why a small percentage change in the largest reservoir could still matter for the atmosphere.

During the Carboniferous Period, huge swampy forests covered parts of what is now the eastern United States. Explain how the growth, death, and burial of these plants removed carbon dioxide from the atmosphere, and what form the carbon eventually took. Then state one way that process is related to the coal that Americans burn today.

Emma studies a graph from a long-term record of atmospheric carbon dioxide measured on Mauna Loa, Hawaii. The curve rises over many years but also shows a regular zigzag, with a peak each spring and a low each late summer or early fall in the Northern Hemisphere. Explain both features. Identify which biological process causes the yearly zigzag, why the low occurs when it does, and which human activity best explains the long-term rise. Use the terms reservoir, flux, and photosynthesis in your answer.

Analyze how biological processes changed the carbon cycle over Earth's history. In your answer, (a) describe how the evolution of photosynthesis changed the atmosphere's carbon dioxide and oxygen, (b) explain how the evolution of shell-building marine organisms created a new long-term carbon reservoir, and (c) compare the timescale of these natural changes with the timescale on which burning fossil fuels is now moving carbon. Conclude with one sentence stating why the speed of the change matters for Earth's systems.