shazmosushi | 5:33
Timeline: The evolution of life
The University of Michigan's Global Change Courses, part of the Program in the Environment, offer a modern approach to undergraduate science and social science education. In interdisciplinary courses the topic of Global Change from physical and human perspectives are examined, and case studies are used to explore scenarios for sustainability. Small, GSI-led group sessions promote critical thinking and analysis.
The courses are aimed at first and second year students who want to understand the historical and modern aspects of Global Change and Sustainability. These 4-credit courses include laboratory sections and carry distribution credit. email@example.com
Composition, Structure And Energy
- How did the atmosphere evolve into what it is today?
- What gases in the atmosphere are important to life and how are they maintained?
- What natural variations occur in atmospheric constituents and what are the important time scales for change?
- Chemical/ pre-biological era
- Microbial era, and
- Biological era.
- Carbon Dioxide
- Chlorofluorocarbons (CFCs)
- Nitrous Oxide
- Atmospheric evolution progressed in four stages, leading to the current situation. The atmosphere has not always been as it is today - and it will change again in the future. It is closely controlled by life and, in turn, controls life processes. Complex feedback mechanisms are at play that we do not yet understand.
- Oxygen became a key atmospheric constituent due entirely to life processes. It built up slowly over time, first oxidizing materials in the oceans and then on land. The current level (20%) is maintained by processes not yet understood.
- Sometime just before the Cambrian, atmospheric oxygen reached levels close enough to today's to allow for the rapid evolution of the higher life forms. For the rest of geologic time, the oxygen in the atmosphere has been maintained by the photosynthesis of the green plants of the world, much of it by green algae in the surface waters of the ocean.
- Selective absorbers in our atmosphere keep the surface of the earth warmer than they would be without an atmosphere.