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Geological History of Oxygen


Explore the changes in oxygen levels throughout Earth’s history and discover their impact on life.

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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 influenced the changes in O2 levels. 

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  • 2012 Association of Medical Illustrators Salon; Award of Excellence 

"I am spreading the word to my higher ed colleagues about using HHMI resources in their lectures. They work! As an example, when lecturing to my Introductory Biology class on the role of oxygen, I assign a primary literature paper (Crowe et al. 2003. Atmospheric oxygenation three billion years ago. Nature 501: 535–538) before the lecture. During class, I use the Geological History of Oxygen Click & Learn. I click on "Howie" in the Archean environment and show the graphics of the world with and without O2, which explain the evidence for a reducing atmosphere when life originated on the planet. I then present the evidence for a reducing atmosphere from what we know about the distribution of chromium isotopes as explained in the Nature paper I assigned. The combination of the first-rate graphics and a recent primary literature paper drive home the point that our understanding of the ancient world is not so ancient and is constantly being updated."

— Fred Wasserman (Boston University, MA)