Current consumption of fossil fuel releases more than 25 billion tons of CO2 into the atmosphere every year. If current trends continue, there will be a tripling of atmospheric CO2 by the end of the century—levels not seen for more than 40 million years. By measuring our carbon footprint, we can...
Grade Level   4 5 6 7 8 9 10 11 12
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Today, oxygen, or O2, makes up about 21% of Earth's atmosphere, but for most of our planet's long history, O2 levels in the atmosphere and dissolved in the ocean were much less than they are today. In this Click and Learn, you will learn the complex biological and geological factors that have...
Grade Level   K 1 2 3 4 5 6 7 8 9 10 11 12
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