4.1.1 - The Atmosphere (KQ1): Atmospheric Structure

ALL energy on the earth comes from the sun.  The atmosphere is the region of space occupied by gases above the lithosphere, extending to space.  The atmosphere protects us from intense energy from the sun and stores the oxygen we need to breathe.

The atmosphere has changed of the course of Earth's history.  Early on, volcanoes gave off massive amounts of carbon dioxide and nitrogen.  Then, over 2 billion years ago, small organisms began making oxygen.  Once enough oxygen had formed the ozone layer, plants an life forms were protected enough to be able to start to appear.

The overall composition of the atmospheric gases is as follows:

Nitrogen - 78% 

Oxygen - 21% 

Water Vapor – 0 to 4% (depends on region...clouds/rain/snow)

Carbon Dioxide - .037% (needed to keep Earth from being ice-cold and is 'plant food')

Argon - .93% 

Traces gases: neon, helium, methane, krypton, xenon, hydrogen, and ozone 

The atmosphere is classified into 4 distinct layers with their own characteristics:

Troposphere

• Lowest layer – extends up to 10km from the crust
• Contains 99% of the water vapor and 75% of the atmospheric gases 
• Weather occurs here
• Most of the layer’s heat is from the Earth itself
• Temperature cools about 6.5 degrees Celsius per kilometer of altitude. (Cooler as you go up)
• Density of air particles decreases with altitude

Stratosphere

• Directly above troposphere, extending from 10 km to about 50 km above Earth’s surface
• Temperature gets WARMER as you increase in this layer
• Density of air particles increases with altitude
• Major home of high levels of a gas called ozone 
• The ozone layer absorbs harmful rays from the Sun
• Layer of 3-atom molecules that protects the Earth from the Sun’s harmful ultraviolet radiation
• Pollutants called chlorofluorocarbons (CFCs) are destroying the ozone 
• Ozone layer has a large hole over Antarctica and a smaller one over the North Pole 
• Currently closing due to CFC reduction efforts! #win

Mesosphere

• Extends from the top of the stratosphere to about 85 km above Earth 
• Coldest layer with little ozone 
• Meteors or rock fragments burn up here 
• Temperatures decrease with altitude
• Density of air particles decreases with altitude

Thermosphere (ionosphere)

• Thickest atmospheric layer found between 85 km and 500 km above Earth’s surface
• Contains auroras (northern lights)
• Very high temperatures
• Very little air particles
• Warmed as it filters out X-rays and gamma rays from the Sun

Check out this image that shows descriptions for each layer.  Notice the temp graph on the right...this is very important to remember:

The following video gives a pretty good explanation of weather balloons and how the hep us determine different properties, including the structure: