Chapter 18

Atmosphere

Earth’s Atmosphere

Earth’s atmosphere, is a thin layer of air that forms a protective covering around the planet.

The atmosphere maintains a balance between the amount of heat absorbed by the sun and the amount of heat that escapes back out into space.

It also, gives Earth’s life forms protection from the sun’s UV rays.

Makeup of the atmosphere

The atmosphere is a mixture of gases, solids, and liquids that surround the planet, and it extends from the surface of the earth to outer space.

The original atmosphere of earth is said to have been made up of CO2, and nitrogen, but very little oxygen.

As organisms, like bacteria, evolved they began to release oxygen as a by product, when they made food through photosynthesis.

Makeup of the atmosphere

As time went by the top layer of the atmosphere became very rich in ozone (O3), and allowed green plants to flourish.

This flourishing of plants gave an even larger output of oxygen, and aided in the evolution of other organisms.

Today, 78% of the gas in the atmosphere is Nitrogen, and only 21% is oxygen.

The other 1% includes water vapor, carbon dioxide, methane, and ozone.

Makeup of the atmosphere The atmosphere also

contains small, solid particles of dust, salt, and pollen.

The dust is picked up by wind along with pollen, and the salt is picked up in ocean mist.

Lower Layers of the Atmosphere

The lowest layer of the atmosphere, where almost all of your activity takes place is called the troposphere.

It has 99% of all the water vapor, and 75% of all the other atmospheric gases. All of our weather and clouds occur in the troposphere.

The layer above the troposphere is called the stratosphere and is 11km above the surface and extends to 50km. The ozone layer is located in this layer of the atmosphere.

Upper Layers of the Atmosphere Above the stratosphere is the mesosphere,

which acts to absorb the suns energy. Next, is the Thermosphere, which is the

thickest layer, and has very high temps due to its proximity to the sun.

Within the mesosphere and thermosphere is what is called the ionosphere, which is a layer of electrically charged particles.

The ionosphere allows radio waves to travel from one place to another.

Exosphere

The exosphere starts at the top to the thermosphere and continues until it merges with space. In this region of the atmosphere, Hydrogen and Helium are the prime components.

This is the atmosphere that our space shuttles orbit the earth.

H.W. 433 pg 1-4 & pg 448 1-5

Atmospheric Pressure

Atmospheric gases extend hundred kilometers above the Earth. Earths gravity is responsible for pulling these gases down toward the surface.

It is the weight of these gases, due to gravity, that pushes down on the air in the troposphere and is known as atmospheric pressure.

As you go up in altitude there is less atmospheric pressure because you have less atmospheric layers above you, pushing down on you.

Atmospheric Temperature

Temps of the thermosphere are very high because it is directly exposed to the suns energy. As the suns energy passes through the thermosphere temps slowly decline.

The troposphere could have high temps as well. This is due to the sun warming the surface of earth, which then warms the air in the troposphere.

The ozone layer The ozone layer is held in the stratosphere,

and contains ozone gas, which is 3 oxygen molecules.

This layer shields us from the UV rays from the sun, which could cause skin damage, ike melanoma.

Pollutants, like car exhausts expel things called chlorofluorocarbons which take an O from the O3 molecule and destroys the ozone layer.

When we speak of a hole in the ozone layer, we actually mean that a hole in the atmosphere exists that is allowing harmful amounts of UV light to reach the surface of the earth.

Energy transfer in the Atmosphere

The Sun provides most of earths energy, and when the suns energy is received by the Earth 3 things could happen:

1) Some energy is reflected back into space by clouds.

2) Some is absorbed by the atmosphere

3) Some is absorbed by the surface of the earth.

Heat energy

Heat is the transfer of thermal energy from an object with a higher temp to one with a lower temp.

This transfer of thermal energy occurs in three ways:

1) Conduction- this is the transfer of heat from one molecule to another through physical contact.

If you put a spoon into a hot bowl of soup, the spoon will get warmer because it conducts heat from the hot soup.

Heat energy

Radiation- this is thermal energy that moves away from its source in all directions in the forms of waves. Ex: The suns energy and a microwave oven uses radiation to heat things with thermal energy.

Convection is the transfer of heat by currents within a fluid or a gas.

Ex: hot air rising off the surface of a radiator.

The water cycle All of the water that is part of Earth is called

the hydrosphere. There is a constant cycle of water between

the atmosphere and the hydrosphere that plays a big role in determining weather patterns and climates.

Bodies of water evaporate due to the suns energy and enter the atmosphere as water vapor.

When the water vapor cools it returns to earth as liquid in the form of rain or solid snow.

That cooling process of water vapor is called condensation.

The water cycle

When condensation occurs very high with in the atmosphere, clouds form.

Clouds are made of tiny water droplets that eventually collide with other tiny water droplets to form rain.

The rain that falls from clouds is called precipitation. And completes the water cycle.

H.W pg 438 pg 438 ques. 1-4 pg 448 ques 6-15

Air Movement

Because of certain surface features, Earth gets heated unevenly by the sun. This causes warmer air is some places and cooler air in other places.

When air is heated it expands and is considered to be a low pressure system.

When air is cooled it contracts and is considered to be a high pressure system.

Wind is the transfer of high pressure air to an area of low pressure air.

Air Movement

So, cold air from the poles moves toward the hot air near the equator in the form of convection (wind) currents.

The earths rotation causes the deflection of air in different directions. Wind moving north above the equator is deflected to the right.

Air moving south below the equator is deflected to the left.

http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/fw/crls.rxml

Global winds Sea breeze- these are winds that blow from

the sea or ocean over land, during the day. This occurs b/c during the day the land is heated more than the water and the high pressure air over the water moves to the lower pressure air over the land.

Land breezes- are the complete opposite of sea breezes and occur at night. This occurs b/c at night the land cools faster than the water.

H.W. due next class on looseleaf pg 450 ques 1-19