Unit 3: Gases and the Atmosphere

Atmosphere: the mass of air surrounding the earth.

Today’s Composition of the Atmosphere

Has the composition of the atmosphere of the earth changed over time?

Yes. The atmosphere has evolved over time, just like everything else. 1. Origin2. Chemical Era3. Microbial Era4. Biological Era

The Biological Era• 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.

• Oxygen was built up slowly over time, first oxidizing materials in the oceans and then on land

• 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.

Sources of Oxygen• Oxygen is liberated as a by-product of photosynthetic chemical reactions.• Oxygen occurs in the atmosphere when water molecules are split apart after

being struck with UV radiation. This process is called photolysis. – H2O H2 + O – The hydrogen molecule is light, and has a quick thermal velocity,so it can escape

Earth's atmosphere leaving behind the free oxygen to form O2 and O3. The main source of this atmospheric water was volcanic eruptions and outgassing.

Basically before photosynthesis began on large scales, free oxygen molecules in the atmosphere were drawn down in oxidation reactions with free metal ions on the Earth's surface, mainly iron. Even when photosynthetic organisms were taking control of the atmosphere, the free oxygen molecules were being placed into the rock record in oxidation reactions. This forms red colored rocks, like you find in the southwestern United States. Because of this, early Earth had a reducing atmosphere, composed mainly of methane,carbon dioxide, water, carbon monoxide, and nitrogen. This would be a very hostile place to most modern forms of life.

Ozone

• Proved to be important in filtering out the high damaging levels of radiation from the sun. This led to the development of more complex species.

CO2 Levels over TimeYear CO2 Concentration (ppmv) T Anomaly (°C off normal)

1840 280 -0.40

1955 310 -0.05

1960 312 0.00

1965 316 -0.10

1970 320 -0.08

1975 327 -0.08

1980 335 -0.08

1985 345 +0.10

1990 352 +0.15

1995 355 +0.25

2000 360 +0.28

Based on this information:

• What conclusions can you draw from ONLY studying this data?

Autism and Vaccines

The real cause of autism?

CO2 Assignment

Research average temperatures in Manitoba and CO2 levels. Graph the results.

1. Describe what information you can interpret from the graph. 2. Why are levels of CO2 increasing?

3. How is this increase leading to climate change?4. Do you think CO2 levels will stop increasing?