Lecture 6

6/11/07

Ast 1001

Earth’s Atmosphere

• The Earth’s atmosphere has several very important properties:– Just enough warmth– Just enough pressure– Water can exist in three phases– Protects us from solar radiation– Allows for weather

The Big Questions

• Why did Earth retain most of its outgassed water?

• Why does Earth have so little carbon dioxide compared to Venus?

• Why does Earth have so much Nitrogen and Oxygen?

• Why does Earth have a UV absorbing stratosphere?

Water and Carbon Dioxide

• Temps were low enough for water vapor to condense– Earth had oceans 4.3 billion years ago

• Ocean’s explain why there is so little carbon dioxide in atmosphere– Most of the carbon dioxide dissolved into the

oceans

Nitrogen and Oxygen

• We have so much nitrogen because it isn’t absorbed as much as carbon dioxide

• Life is key to explaining why we have so much oxygen– Oxygen breaks down after several millions of

years– Also explains why we have an ozone layer

Earth’s Stable Climate

• Earth has a relatively stable climate• Earth self regulates via the carbon dioxide cycle

– Atmospheric carbon dioxide dissolve into rainwater

– Rain erodes the rocks, bringing minerals to the oceans

– Calcium combines with carbon dioxide and makes rocks like limestone

– Plate tectonics carry the rocks to the subduction zone

– Rock melts and releases its carbon dioxide back into the atmosphere through volcanoes

Feedback• What if Earth warms up?

– More evaporation and rainfall

– More carbon dioxide out of the atmosphere

– Weaker greenhouse effect

• What if Earth cools down?– Less rainfall– More carbon dioxide in the

atmosphere– Stronger greenhouse effect

Long Term Change• It takes the carbon dioxide

cycle time to stabilize the temps– We can have ice ages or hot

spells

– Geologists have discovered a snowball Earth phase

• Eventually the gradually brightening Sun will cause major climate issues

Humans and Climate

• It is undeniable that humans affect climate and our planet– Ozone layer hole– Mass extinctions

Global Warming• There is controversy about how

serious the problem is, but the following facts are clear:– Measurements show that the Earth

has warmed over the past 50 years

– The burning of fossil fuels and other human activity dumps greenhouse gasses into the atmosphere

– Eventually, a continually rising concentration of greenhouse gasses would make our planet warm up