The Earth’s Atmosphere

Lab: Beware of “Air”!

The Earth is protected by a blanket of air called the atmosphere.

The atmosphere is held in place by gravity, extending from the surface to an altitude of hundreds of kilometers.

This blanket protects us.

Without our atmosphere, the Earth’s surface would like the moon’s.

Our atmosphere also protects the Earth from solar radiation.

The Martian atmosphere is very thin which results in only a weak protection from the Sun’s Radiation.

Like a prism, the Earth’s atmosphere refracts the Sun’s light.

This refraction of the Sun’s light gives the atmosphere its blue color.

The earliest atmosphere, some 4.5 billion years ago, was sterile, and with no free oxygen.

Early atmospheric evolution was driven by carbon dioxide dissolving in the ocean and chemical reactions caused by rock weathering, solar radiation and lightning.

Volcanic activity released an abundant supply of “greenhouse gases” into the atmosphere.

CH 4 & CO 2

Cyanobacteria Methanogens

By one billion years ago enough oxygen was being produced that would protect the surface from harmful solar radiation, and enable life to extend from the protection of the ocean to dry land.

Lab: Parts per Million

Atmosphere Layers

Nearest to the surface of Earth is the troposphere. Nearest to the surface of Earth is the troposphere.

It is the densest part of the atmosphere that interacts directly with land, water and life.

All weather phenomena occur within the troposphere which contains 99% of the water vapor that resides in the atmosphere.

For the next 30 miles above the Troposphere is the Stratosphere.

In this layer there is basically no weather. Jet pilots fly there to avoid storms.

This is a layer with a very large temperature change. It changes from cold to warm.

This temperature increase is due to the presence of ozone.

Inside the Stratosphere, this ozone forms a protective layer.

This layer contains 90% of the atmospheric ozone which absorbs incoming ultraviolet energy.

If all of the Ozone in the Earth's atmosphere were compressed into a single layer at the Earth's surface, it would only be 3 millimeters thick- basically two stacked pennies!

The Mesosphere starts just above the Stratosphere and extends to 85 kilometers (53 miles) high.

It is the coldest of all the layers in the entire atmosphere. Temperatures fall as low as -93ºC!

The next layer is the Thermosphere which starts just above the Mesosphere and extends to 600 kilometers (372 miles) high.

Temperatures in this region can go as high as 1,727ºC!

A portion of the Thermosphere is called the Ionosphere because the air there is highly ionized.

The Ionosphere has a practical importance because, among other functions, it influences radio propagation to distant places on the Earth.

The Exosphere is the uppermost layer of the atmosphere.

According to the NASA, space starts 62 miles (100 km) above the planet's surface.

Heat Transfer in the Atmosphere

The major source of Earth’s heat energy comes from the sun.

The Sun’s heat energy travels the 152,1000,000 kilometers by Radiation.

Radiation is heat transfer through wave energy.

These waves are called Electromagnetic Waves, because the energy travels in a combination of electric and magnetic waves.

This energy is released when these waves are absorbed by an object.

Lab: Radiation

The other source of Earth’s heat energy comes from the Earth’s core.

Conduction is the transfer of heat within a substance, molecule by molecule.

Lab: Macho Conduction

Lab: What are “R” Values

This explains the principle of Geothermal Heating!

Convection is heat transfer by the mass movement of a fluid in the vertical (up/down) direction.

This type of heat transfer takes place in liquids and gases.

Lab: Conduction & Convection

Convection vs. Radiant

Lab: Soil vs. Water

Why do temperatures vary place to place?

Temperatures around the world vary greatly.

Lab: Temperature Maps

The Earth's axis always remains pointing in the same direction as it revolves around the sun.

As a result, the solar angle varies at a given place throughout the year.

The variation in sun angle is the prime cause of our seasons. The orientation of the Earth with respect to the Sun also determines the length of day.

Lab: Reasons for the Seasons

Atmosphere in Motion

Air is constantly moving across the face of the Earth!

Wind is the horizontal movement of air!

Factors Affecting Wind Air Pressure

Air Pressure is the weight of the atmosphere as it pushes down upon the Earth’s surface.

Existence of Air Pressure

Lab: Under Pressure

High Pressure tends to sink while Low Pressure tends to rise.

Air pressure decreases as elevation increases.

Wind is caused by air flowing from high pressure to low pressure.

Wind direction is influenced by the Earth’s rotation.

If the Earth did not rotate, air would flow straight up & down from high pressure to low pressure.

Winds seldom move in a straight path.

Factors Affecting Wind The Coriolis Effect

Global Wind Patterns

Each hemisphere has 3 air circulation cells.

Trade winds occur in the tropics between the equator and the Tropic of Cancer in the north and the equator and Tropic of Capricorn in the south.

In the northern hemisphere, the prevailing winds are Westerlies. In the southern hemisphere the prevailing winds are Easterlies.

Polar Easterlies occur at the North Pole and Polar Westerlies at the South Pole.

Jet stream winds (120 km/h-240 km/h) are high altitude winds.

Factors Affecting Wind Land-Sea Breeze Circulation

Lab: Wind Speed