Human earth shapers/ETHS101/Earth Systems Exchange/System Exchange

System Exchange - The first earth shaping

(Cyanobacteria): Mixture; native preparation; green filter

Early Earth's atmosphere and oceans would have been toxic to us. There was no free O2. Archaea are a branch of life that can tolerate extreme conditions. They were probably widespread at this time. They are still with us today, but tend to hide away as oxygen is toxic to many of them. Because they can live in hydrothermal vents, geysers and hot springs where the fluids are as acidic as battery acid and temperatures are between 60 and 100 degrees Celsius, they are called extremophiles. They are what astrobiologists look for on Mars.

The rise of free oxygen in the Earth's oceans and atmosphere was caused by another micro-organism. It was cyanobacteria which consume CO2 and expel oxygen and eventually changed Earth's environment into a habitable planet for all the life that evolved after. As the oceans became saturated in oxygen, oxygen could escape into the atmosphere. It is estimated that around 2.4 billion years ago there was an event called 'The Great Oxygenation Event', that marks the rise of atmospheric oxygen. Here is an example of the biosphere changing the environment and probably precipitating the first mass extinction of micro-organisms

Feedback in systems

The exchange of material, and in particular, the exchange of carbon, between the biosphere, hydrosphere and atmosphere, is critical for maintaining a habitable earth. This page explores some of the important exchanges between earth's carbon reservoirs, and introduces the concept of feedbacks in the earth system

Hypothesis Activity

• Read Chapter 7 of How to build Habitable Planet: Making it Comfortable page 197 - 214

Use these questions to help you identify key concepts within the reading.

1. Why is Venus so much warmer than Earth today?
2. What factors explain why Earth is habitable today?
3. Why does the faint young Sun pose a paradox?
4. What evidence suggests that Earth has always had a long-term thermostat regulating its climate?
5. Why is volcanic input of CO2 to Earth’s atmosphere not a candidate for its thermostat?
6. What climate factors affect the removal of CO2 from the atmosphere by chemical weathering?
7. Where did the extra CO2 from Earth’s early atmosphere go?

Learning Pathway Quiz

For each of the following questions, select the answer that appears in the correct order.

• Sort these reservoirs of carbon in order of increasing size (gigatons)
  • Atmosphere, Deep Ocean, Sediments and Rocks
    • Correct. Sediments and rocks contain by far the largest amount of carbon on earth, next comes the deep ocean. The atmosphere contains relatively little carbon, and responds to changes in the size of the other reservoirs.
  • Sediments and Rocks, Atmosphere, Deep Ocean
    • Incorrect. Consider the role of radiometric dating, that might provide you with a clue to which carbon reservoir has the most carbon.
  • Deep Ocean, Atmosphere, Sediments and Rocks
    • Incorrect. Consider the role of radiometric dating, that might provide you with a clue to which carbon reservoir has the most carbon.
  • Sediments and Rocks, Deep Ocean, Atmosphere
    • Incorrect. Consider the role of radiometric dating, that might provide you with a clue to which carbon reservoir has the most carbon.
• Which carbon reservoirs have the slowest exchange rates (gigatons/year).
  • surface ocean to atmosphere
    • Incorrect. Try again, consider the size of carbon reservoirs.
  • vegetation to atmosphere
    • Incorrect. Try again, consider the size of carbon reservoirs.
  • sediments and rocks to atmosphere,
    • Correct. Generally, the larger carbon reservoirs exchange more slowly than the smaller reservoirs. So volcanoes only affect atmospheric CO2 over long geological time periods (millions of years)
• As described in the reading and in the diagram above from the reading, chemical weathering links the geosphere, the hydrosphere and the atmosphere through carbon exchange. How does the "chemical weathering thermostat" help to explain the faint young sun paradox? Pick one or more of the options below.
  • Chemical weathering would have been slow early in earth's history when the sun was faint, thereby leaving more carbon in the atmosphere, which would warm the planet
    • Correct. The cold temperatures of early earth would mean slow rates of chemical weathering. Plus, there were no plants around, another factor that would lead to slow rates of chemical weathering. Finally, the continents covered a smaller area, so there would have been less land surface for chemical weathering
  • As the sun brightened the warming would have increased rates of chemical weathering which would have removed carbon from the atmosphere, helping to offset the warming sun
    • Correct. This is the thermostat aspect of chemical weathering- because its rate depends on climate (temperature and precipitation), an initial bit of warming caused by increased brightness of the sun would increase the rate of chemical weathering, which in turn removes carbon dioxide, and which leads to cooling. The chemical weathering feedback therefore acts to dampen climate change (not eliminate it entirely). 
  • Chemical weathering would have been faster early in earth's history, thereby adding carbon to the atmosphere, which would warm the planet
    • Incorrect. Chemical weathering is slower at cold temperatures, and chemical weathering removes, not adds, carbon to the atmosphere