Plant fossils tell stories about ancient atmospheres. Beth Tyler 06.01.01 Plants perform photosynthesis, creating sugar from sunlight and carbon dioxide. Before they can do this, plants have to get carbon dioxide into their leaves. They do this using stomata, small openings on the leaf surface that absorb carbon dioxide from the air. When there is a lot of carbon dioxide in the air, plants don’t need as many stomata to absorb enough carbon dioxide for photosynthesis. Therefore, the more carbon dioxide there is in the air, the fewer stomata a plant leaf will have. Using this information, scientists can study ancient plant remains to figure out how much carbon dioxide was present in the air of ancient atmospheres.     An American scientist studied leaf fossils from Gingko (species in the genus Gingko) and other plants from 300 million years ago to today. He counted the number of stomata in a constant area of each leaf. This number allowed the scientist to estimate the amount of carbon dioxide present in the atmosphere at the time the leaf lived. The scientist used this information to figure out how the amount of carbon dioxide in the air changed over the 300 million years. He found that in the past 300 million years carbon dioxide levels have gone up and down, with a big increase in the past 200 years. He also found that times with high carbon dioxide in the air had high temperatures.   Retallack, Gregory J. 2001. A 300-million-year record of atmospheric carbon dioxide from fossil plant cuticles. Nature 411: 287- 290. ©2001 The Aurora Collection, Inc. All Rights Reserved. Site Development by: Interactive Multimedia. Inc.