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Here are four different ways chemists use to show a molecule of carbon dioxide. In the colored molecule models, carbon is light gray and oxygen is red.
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Windows to the Universe original artwork by Randy Russell.

Carbon Dioxide - CO2

Carbon dioxide (CO2) is a kind of gas. There isn't that much carbon dioxide in Earth's atmosphere, but it is still very important. Carbon dioxide is a greenhouse gas. That means it helps trap heat coming from the Sun in our atmosphere through the greenhouse effect. Without carbon dioxide in our air, the Earth would be very cold.

Where does the carbon dioxide in our air come from? When humans and other animals breathe, we take in oxygen and breathe out carbon dioxide. We use the oxygen to get energy from food - this is called respiration.

Burning things also makes lots of carbon dioxide. Natural fires like forest fires make carbon dioxide. Things that humans burn make CO2, too. The smokestacks of factories that burn coal give off carbon dioxide. The engines of cars, trucks, and buses also pump carbon dioxide into the air. They sometimes give off another gas, carbon monoxide, too.

Earth isn't the only place where carbon dioxide is important. Most of the atmosphere of Venus is CO2. The atmosphere of Mars is also mostly carbon dioxide. If carbon dioxide gets really cold, it can freeze into a solid. This kind of ice is called "dry ice". The polar ice caps on Mars are partly made of dry ice!

Last modified October 15, 2011 by Jennifer Bergman.

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Our online store includes fun classroom activities for you and your students. Issues of NESTA's quarterly journal, The Earth Scientist are also full of classroom activities on different topics in Earth and space science!

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA