History
Earth is believed to have formed about
5 billion years ago. In the first 500
million years a dense atmosphere
emerged from the vapor and gases that
were expelled during degassing of the
planet's interior. These gases may have
consisted of hydrogen (H2), water
vapor, methane (CH4) , and carbon oxides. Prior to 3.5 billion years ago the
atmosphere probably consisted of carbon dioxide (CO2), carbon monoxide (CO),
water (H2O), nitrogen (N2), and hydrogen.
The hydrosphere was formed 4 billion years ago from the condensation of
water vapor, resulting in oceans of water in which sedimentation occured.
The most important feature of the ancient environment was the absence of free
oxygen. Evidence of such an anaerobic reducing atmosphere is hidden in early
rock formations that contain many elements, such as iron and uranium, in their
reduced states. Elements in this state are not found in the rocks of midPrecambrian and younger ages, less than 3 billion years old.
One billion years ago, early aquatic organisms called bluegreen algae began using energy from the Sun to split
molecules of H2O and CO2 and recombine them into
organic compounds and molecular oxygen (O2). This solar
energy conversion process is known as photosynthesis.
Some of the photosynthetically created oxygen combined
with organic carbon to recreate CO2 molecules. The
remaining oxygen accumulated in the atmosphere, touching off a massive
ecological disaster with respect to early existing anaerobic organisms. As
oxygen in the atmosphere increased, CO2 decreased.
High in the atmosphere, some oxygen (O2) molecules absorbed energy from
the Sun's ultraviolet (UV) rays and split to form single oxygen atoms. These
atoms combining with remaining oxygen (O2) to form ozone (O3) molecules,
which are very effective at absorbing UV rays. The thin layer of ozone that
surrounds Earth acts as a shield, protecting the planet from irradiation by UV
light.
The amount of ozone required to shield Earth from
biologically lethal UV radiation, wavelengths from 200
to 300 nanometers (nm), is believed to have been in
existence 600 million years ago. At this time, the
oxygen level was approximately 10% of its present
atmospheric concentration. Prior to this period, life
was restricted to the ocean. The presence of ozone
enabled organisms to develop and live on the land.
Ozone played a significant role in the evolution of life
on Earth, and allows life as we presently know it to
exist.
Present-Day Composition
A. Nitrogen - 78% Dilutes oxygen and
prevents rapid burning at
the earth's surface.
Living things need it to
make proteins. Nitrogen
cannot be used directly
from the air. The
Nitrogen Cycle is nature's way of supplying the needed nitrogen
for living things.
B. Oxygen - 21% - Used by all living things.
Essential for respiration. It is necessary for
combustion or burning.
C. Argon - 0.9% - Used in light bulbs.
D. Carbon Dioxide - 0.03% - Plants use it to
make oxygen. Acts as a blanket and prevents
the escape of heat into outer space. Scientists are afraid that
the buring of fossil fuels such as coal and oil are adding more
carbon dioxide to the atmosphere.
E. Water Vapor - 0.0 to 4.0% - Essential for life processes. Also
prevents heat loss from the earth.
F. Trace gases - gases found only in very small amounts. They
include neon, helium, krypton, and xenon.
Structure
The Atmosphere is divided into layers according to major
changes in temperature. Gravity pushes the layers of air
down on the earth's surface. This push is called air
pressure. 99% of the total mass of the atmosphere is
below 32 kilometers.
Troposphere - 0 to 12 km - Contains 75% of the gases in the
atmosphere. This is where you live and where weather occurs.
As height increases, temperature decreases. The temperature
drops about 6.5 degrees Celsius for every kilometer above the
earth's surface.
o
Tropopause - located at the top of the troposhere. The
temperature remains fairly constant here. This layer
separates the troposphere from the stratosphere. We find
the jet stream here. These are very strong winds that blow
eastward.
Stratosphere - 12 to 50 km - in the lower part of the
stratosphere. The temperature remains fairly constant (-60
degrees Celsius). This layer contains the ozone layer. Ozone
acts as a shield for in the earth's surface. It absorbs ultraviolet
radiation from the sun. This causes a temperature increase in
the upper part of the layer.
Mesophere - 50 to 80 km - in the lower part of the stratosphere.
The temperature drops in this layer to about -100 degrees
Celsius. This is the coldest region of the atmosphere. This layer
protects the earth from meteoroids. They burn up in this area.
Thermosphere - 80 km and up - The air is very thin.
Thermosphere means "heat sphere". The temperature is very
high in this layer because ultraviolet radiation is turned into heat.
Temperatures often reach 2000 degrees Celsius or more. This
layer contains:
2.
Ionosphere - This is the lower part of the thermosphere. It
extends from about 80 to 550 km. Gas particles absorb
ultraviolet and X-ray radiation from the sun. The particles of gas
become electrically charged (ions). Radio waves are bounced
off the ions and reflect waves back to earth. This generally helps
radio communication. However, solar flares can increase the
number of ions and can interfere with the transmission of some
radio waves.
3. Exosphere - the upper part of the thermosphere. It
extends from about 550 km for thousands of kilometers.
Air is very thin here. This is the area where satellites orbit
the earth.
Magnetosphere - the area around the earth
that extends beyond the atmosphere. The
earth's magnetic field operates here. It begins
at about 1000 km. It is made up of positively
charged protons and negatively charged
electrons. This traps the particles that are
given off by the sun. They are concentrated into belts or
layers called the Van Allen radiation belts. The Van Allen
belts trap deadly radiation. When large amounts are given
off during a solar flare, the particles collide with each other
causing the aurora borealis or the northern lights.
Activity: Atmosphere Riddles
Directions:Write the name of the layer or part of the atmosphere that answers the
riddles. Use the link below to search for the answers.
1. I have the coldest temperature of the atmosphere.
Who am I?_______________________________
2. I am where most of the weather occurs.
Who am I?_______________________________
3. I contain most of the ozone layer.
Who am I?_______________________________
4. Artificial satellites orbit the earth here.
Who am I?_______________________________
5. I protect the earth from meteoroids.
Who am I?_______________________________
6. I protect the earth from ultraviolet rays given off by the sun.
Who am I?_______________________________
7. I am where radio waves are bounced back to the earth's
surface.
Who am I?_______________________________
8. I extend to an average altitude of about 12 km.
Who am I?_______________________________
9. My temperature may reach as high as 2000 degrees celsius.
Who am I?_______________________________
10.
Convection currents are produced in my layer.
Who am I?_______________________________
11.
I am the layer that touches the surface of the earth.
Who am I?_______________________________
12.
I am the layer that reaches the highest altitude.
Who am I?_______________________________
13.
The jet stream is located here.
Who am I?_______________________________
14.
I extend to an alititude from about 50 km to 80 km.
Who am I?_______________________________
15.
I am the layer that interacts with living things.
Who am I?_______________________________
16.
I extend upwards from an altitude of about 550 km to
1000 km.
Who am I?_______________________________
17.
The air pressure is the greatest here.
Who am I?_______________________________
18.
Electrically charged particles called ions are found here.
Who am I?_______________________________
19.
My temperature drops about 6.5 degrees Celsius per km.
Who am I?_______________________________
20.
I extend to an altitude of about 12 km to 50 km.
Who am I?_______________________________
Directions:Check your answers.
1. I have the coldest temperature of the atmosphere.
Who am I? Mesosphere
2. I am where most of the weather occurs.
Who am I? Troposphere
3. I contain most of the ozone layer.
Who am I? Stratosphere
4. Artificial satellites orbit the earth here.
Who am I? Exosphere
5. I protect the earth from meteoroids.
Who am I? Mesosphere
6. I protect the earth from ultraviolet rays given off by the sun.
Who am I? Stratosphere (Ozone)
7. I am where radio waves are bounced back to the earth's
surface.
Who am I? Ionosphere
8. I extend to an average altitude of about 12 km.
Who am I? Troposphere
9. My temperature may reach as high as 2000 degrees celsius.
Who am I? Thermosphere
10.
Convection currents are produced in my layer.
Who am I? Troposphere
11.
I am the layer that touches the surface of the earth.
Who am I? Troposphere
12.
I am the layer that reaches the highest altitude.
Who am I? Thermosphere
13.
The jet stream is located here.
Who am I? Troposphere
14.
I extend to an alititude from about 50 km to 80 km.
Who am I? Mesosphere
15.
I am the layer that interacts with living things.
Who am I? Troposphere
16.
I extend upwards from an altitude of about 550 km to
1000 km.
Who am I? Exosphere
17.
The air pressure is the greatest here.
Who am I? Troposphere
18.
Electrically charged particles called ions are found here.
Who am I? Ionosphere
19.
My temperature drops about 6.5 degrees Celsius per km.
Who am I? Troposphere
20.
I extend to an altitude of about 12 km to 50 km.
Who am I? Stratosphere