THE ATMOSPHERE Earth’s atmosphere is UNIQUE! No other planet has the mixture of gases that we have that are vital to our existence. From the ground it is hard to tell, but there is a lot going on in the sky that all life on Earth needs to appreciate

Changing composition of air The atmosphere was thought to have started as gases emitted during volcanic eruptions Evidence shows that oxygen did not start to accumulate until 2.5 billion years ago Atmosphere continues to exchange material with oceans and life on Earth’s surface.

Composition of Atmosphere Nitrogen (78%) and oxygen (21%) dominate the volume of gases composing dry air

Structure of the Atmosphere  The atmosphere rapidly thins as you travel away from Earth until there are too few gas molecules to detect. Pressure Changes Atmospheric pressure is simply the weight of the air above.

Height and Structure of the Atmosphere can be divided vertically into Four layers based on temperature.

• Troposphere = bottom layer of the atmosphere, temperature decreases with an increase in altitude. (where weather occurs) • Stratosphere = gradual increase in temp. (contains the OZONE layer)

• Mesosphere = characterized by decreasing temperatures with height • Mesosphere = characterized by decreasing temperatures with height. (where shooting stars burn up, meteors) *** COLDEST layer of the atm Thermosphere = characterized by increasing temperatures due to the absorption of very short-wave, high energy solar radiation by nitrogen & oxygen. *** Warmest layer of the atm

Weather vs. Climate Climate Weather is constantly changing! Weather is the state of the atmosphere at any given time and place. Climate based on observations of weather that have been collected over many years = “AVERAGE WEATHER” (helps describe a place or region ). Ex: farmer’s need to know the AVERAGE rainfall for growing season