Earth, Page 33: [Previous Page] [Next Page] [Class Home Page] Textbook pages 130 - 131

Changes in Earth's Atmosphere from Biological Activity

We hear a lot today about humanities effect on the atmosphere and air pollution. However, not all biological activity has been entirely bad!

Cyanobacteria. Creators of our Oxygen Atmosphere
Still around today, cyanobacteria are aquatic (live in water) and photosynthetic (can manufacture their own food). They are extremely small, usually unicellular, though can form large colonies. They have been identified in fossils more than 3.5 billion years old.

Cyanobacteria have been tremendously important in the shaping of Earth's atmosphere. Via photosynthesis, they are responsible for having brought about Earth's Oxygen Atmosphere beginning about 3.5 billion years ago and it continues today. Oxygen gas was a pollutant at the time.

Modern Pollutants
Carbon monoxide is a odorless, poisonous gas. It is created when gasoline does not completely burn. 60 million metric tons of carbon monoxide gets put into the air each year in the United States. Many fear the release of so much carbon in the air will trigger Global Warming due to a heightened greenhouse effect.

Will the Earth's carbon cycle buffer us to the changes?
It's not really known. If the temperature of the Earth rises, then the oceans may absorb more carbon. However, the damage will already be done. Predicted changes 1) Heat waves, 2) Sea levels rising and coastal flooding, 3) Glaciers Melting, 4) Arctic and Antarctic warming. These signposts of global warming may already be occurring. By the time we confidently measure a change in temperature, it will already be too late. We are running an uncontrolled, irreparable experiment.

What about the Ozone Hole?
Ozone naturally forms high in our atmosphere (about 15-30 km up) where a thin amount of oxygen resides. Up there, ultraviolet light is able to penetrate and break up the O₂, and some of it reforms as O₃, ozone. Ozone absorbs X-ray and UV light quite well, not allowing it to penetrate through the rest of the atmosphere to the surface.

The effect of CFCs
CFCs -- "ChloroFluoroCarbons" are released into the air where the complex molecule is broken up. Chlorine and Bromine atoms make their way to the ozone layer in the stratosphere, and tie up the oxygen atoms to keep them from forming into ozone. The effect was heightened in the Antarctic because of unique conditions conducive to ozone destruction (PSCs), though the effect spreads to mid-latitudes.