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# Development of Theories

## A theory as an explanation supported by evidence with no contradictions. This concept introduces three important theories in Earth Science.

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A Gigantic Experiment

### A Gigantic Experiment

Credit: Environmental Protection Agency. Headquarters: Washington, D.C., U.S.A.
Source: http://en.wikipedia.org/wiki/File:Fluctuations_in_temperature_and_in_the_atmospheric_concentration_of_carbon_dioxide_over_the_past_649,000_years.gif

This graph shows the changes in temperature and concentration of carbon dioxide in the atmosphere over the past 649,00 years. Notice the trend is definitely upward.

#### News You Can Use

• Carbon dioxide in the atmosphere reached 400 parts per million on May 9, 2013. While 400 ppm is just an arbitrary number, it highlights that we are in unknown territory. Never before in human history have carbon dioxide levels been so high. It’s like we humans are performing a giant experiment - to our one and only home.
• The Keeling Curve graph shows the level of carbon dioxide in the atmosphere at Mauna Loa volcano. Charles Keeling started the measurements in 1958. The ups and downs are caused by the seasons. In Northern Hemisphere summer, plants take in more carbon dioxide. In winter, they release carbon dioxide. Despite, the squiggles, the overall trend is linear.

#### Explore More

1. How much has carbon dioxide in the atmosphere risen in the past century?
2. What is an experiment? Do you usually know the outcome of an experiment?
3. Why do they call this an experiment?
4. Often in science, researchers have preliminary results before they do the main experiment. What are the preliminary results of this experiment?
5. What will be the final results of this experiment?
6. When you look at the carbon dioxide level of the atmosphere right now the number may be below 400 ppm. Why could it be lower?

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