Earth Science
Chapter 22
Section 1 – Characteristics of the Atmosphere
E.Q.: What is the composition and characteristics of the
Earth’s atmosphere?
STANDARDS:
SES1. Students will investigate the composition and formation of Earth
systems, including the Earth’s relationship to the solar system.
e. Identify the transformations and major reservoirs that make up
the rock cycle, hydrologic cycle, carbon cycle, and other important
geochemical cycles.
SES6. Students will explain how life on Earth responds to and shapes Earth
systems.
c. Explain how geological and ecological processes interact through
time to cycle matter and energy, and how human activity alters
the rates of these processes (e.g., fossil fuel formation and
combustion).
Objectives
• Describe the composition of Earth’s atmosphere.
• Explain how two types of barometers work.
• Identify the layers of the atmosphere.
• Identify two effects of air pollution.
COMPOSITION OF THE ATMOSPHERE
atmosphere - a mixture of gases that surrounds a planet,
such as Earth
• The most abundant elements in air are the gases
nitrogen, oxygen, and argon.
• The two most abundant compounds in air are the gases
carbon dioxide, CO2, and water vapor, H2O.
• In addition to containing gaseous elements and
compounds, the atmosphere commonly carries various
kinds of tiny solid particles, such as dust and pollen.
Pete Turner/Stone Collection/Getty Images/Space Shuttle Images
Objects that enter the Earth's atmosphere face a rough trip.
Nitrogen in the Atmosphere
• Nitrogen makes up about 78% of Earth’s atmosphere
and is maintained through the nitrogen cycle.
• Nitrogen is removed from the air mainly by the action
of nitrogen-fixing bacteria.
• Decay releases nitrogen back into the atmosphere.
Nitrogen is an enormously important element with a versatile chemistry. It is part
of every protein. Our air consists to 78% of N2. The chemical bond between the
two atoms in the nitrogen molecule is the strongest bond between two atoms of
the same element. This makes N2 a very stable and inert gas. Ammonia, NH3, which
itself is toxic, is the most important base material for the nitrogen chemistry and is
one of the most produced chemicals in the world. From this, for example fertilizers
and explosives are made.
Oxygen in the Atmosphere
• Oxygen makes up about 21% of Earth’s atmosphere.
• Land and ocean plants produce large quantities of
oxygen in a process called photosynthesis.
• Animals, bacteria, and plants remove oxygen from the
air as part of their life processes.
Oxygen is the third most abundant element in the universe and makes up nearly 21% of the
earth's atmosphere. Oxygen accounts for nearly half of the mass of the earth's crust, two
thirds of the mass of the human body and nine tenths of the mass of water. Large amounts of
oxygen can be extracted from liquefied air through a process known as fractional distillation.
Oxygen can also be produced through the electrolysis of water or by heating potassium
chlorate (KClO3).
Water Vapor in the Atmosphere
• As water evaporates from oceans, lakes, streams, and
soil, it enters air as the invisible gas water vapor.
• Plants and animals give off water vapor during
transpiration, one of their processes. But as water
vapor enters the atmosphere, it is removed by the
processes of condensation and precipitation.
• The percentage of water vapor in the atmosphere
varies depending on factors such as time of day,
location, and season.
The primary greenhouse gases in the Earth's atmosphere are water vapour, carbon
dioxide, methane, nitrous oxide, and ozone. Greenhouse gases greatly affect the
temperature of the Earth; without them, Earth's surface would be on average about
33 °C (59 °F) colder than at present.
*Transpiration is the process by which moisture is carried through plants from roots
to small pores on the underside of leaves, where it changes to vapor and is released to
the atmosphere. Transpiration is essentially evaporation of water from plant leaves.
Studies have revealed that about 10 percent of the moisture found in the atmosphere
is released by plants through transpiration. The remaining 90 percent is mainly
supplied by evaporation from oceans, seas, and other bodies of water (lakes, rivers,
streams).
READING CHECK:
Does transpiration increase the amount of water vapor in
the atmosphere or decrease the amount of water vapor
in the atmosphere?
Transpiration increases the amount of water vapor in the
atmosphere.
Ozone in the Atmosphere
ozone - a gas molecule that is made up of three oxygen
atoms
• Ozone in the upper atmosphere forms the ozone layer,
which absorbs harmful ultraviolet radiation from the
sun.
• Without the ozone layer, living organisms would be
severely damaged by the sun’s ultraviolet rays.
• Unfortunately, a number of human activities damage
the ozone layer.
Particulates in the Atmosphere
• Particulates can be volcanic dust, ash from fires,
microscopic organisms, or mineral particles lifted from
soil by winds.
Strep throat is caused by group A beta-hemolytic streptococcus.
• Pollen from plants and particles from meteors that
have vaporized are also particulates.
• Large, heavy particles remain in the atmosphere only
briefly, but tiny particles can remain suspended in the
atmosphere for months or years.
Dust storm in Phoenix, Arizona in 2011.
ATMOSPHERIC PRESSURE
atmospheric pressure - the force per unit area that is
exerted on a surface by the weight of the atmosphere
• Gravity holds the gases of the atmosphere near Earth’s
surface. As a result, the air molecules are compressed
together and exert force on Earth’s surface.
Gravitation, or gravity, is a natural phenomenon by which physical bodies attract with a force
proportional to their masses.
• Atmospheric pressure is exerted equally in all
directions—up, down, and sideways.
• Earth’s gravity keeps 99% of the total mass of the
atmosphere within 32 km of Earth’s surface.
• Because the pull of gravity is not as strong at higher
altitudes, the air molecules are farther apart and exert
less pressure on each other at higher altitudes.
Sir Isaac Newton (1642-1727) was an English physicist, mathematician, astronomer, natural
philosopher, alchemist, and theologian, who has been "considered by many to be the greatest
and most influential scientist who ever lived.
• Thus, atmospheric pressure decreases as altitude
increases.
• Atmospheric pressure also changes as a result of
differences in temperature and in the amount of water
vapor in the air.
• In general, as temperature increase, atmospheric
pressure at sea level decreases.
• Similarly, air that contains a lot of water vapor is less
dense than drier air because water vapor molecules
have less mass than nitrogen or oxygen molecules do.
• Barometric Pressure also known as atmospheric
pressure is the same as Air Pressure. The pressure
exerted by the atmoshpere at a given point.
Air Pressure is the weight of the air pushing on Earth.
It can change from place to place which causes air to
move or circulate, flowing from areas of high pressure
toward areas of low pressure. It's the same as
atmospheric pressure.
Air Pressure chances with the weather. In fact, its one
of the most important factors in forecasting approaching
weather and helps determine what the weather will be
like.
Example:
Even though we do not always feel pressure
changes, our bodies are able to detect fast changes. For
example, when flying in a plane and increasing height
quickly, our ears may "pop". This is due to low
atmospheric pressure.
Measuring Atmospheric Pressure
• Meteorologists use three units for atmospheric
pressure: atmospheres (atm), millimeters or inches of
mercury, and millibars (mb).
• Standard atmospheric pressure, or 1 atmosphere, is
equal to 760 mm of mercury, or 1000 millibars. The
average atmospheric pressure at sea level is 1 atm.
• Meteorologists measure atmospheric pressure by using
an instrument called a barometer.
Mercurial Barometers
• Atmospheric pressure presses on the liquid mercury in
the well at the base of the barometer.
• The height of the mercury inside the tube varies with
the atmospheric pressure.
• The greater the atmospheric pressure is, the higher the
mercury rises.
Aneroid Barometers
• Inside an aneroid barometer is a sealed metal
container from which most of the air has been removed
to form a partial vacuum.
• Changes in atmospheric pressure cause the sides of the
container to bed inward or bulge out. These changes
move a pointer on a scale.
• An aneroid barometer can also measure altitude above
sea level.
READING CHECK:
What is inside an aneroid barometer?
An aneroid barometer contains a sealed metal container
that has a partial vacuum.
LAYERS OF THE ATMOSPHERE
• Earth’s atmosphere as a distinctive pattern of
temperature changes with increasing altitude.
• The temperature differences mainly result from how
solar energy is absorbed as it moves through the
atmosphere.
• Scientists identify four main layers of the atmosphere
based on these differences.
The Troposphere
troposphere - the lowest layer of the atmosphere, in which
temperature drops at a constant rate as altitude increases;
the part of the atmosphere where weather conditions exist
• At an average altitude of 12 km, the temperature stops
decreasing. This zone is called the tropopause and
represents the upper boundary of the troposphere.
The Stratosphere
stratosphere - the layer of the atmosphere that lies
between the troposphere and the mesosphere and in which
temperature increases as altitude increases; contains the
ozone layer
• In the upper stratosphere, the temperature increases
as altitude increases because air in the stratosphere is
heated from above by absorption of solar radiation by
ozone.
The Mesosphere
mesosphere - the coldest layer of the atmosphere, between
the stratosphere and the thermosphere, in which the
temperature decreases as altitude increases
• The upper boundary of the mesosphere, called the
mesopause, has an average temperature of nearly
90°C, which is the coldest temperature in the
atmosphere.
The Thermosphere
thermosphere - the uppermost layer of the atmosphere, in
which temperature increase as altitude increases; includes
the ionosphere
• The lower region of the thermosphere, at an altitude of
80 to 400 km, is commonly called the ionosphere.
• Interactions between solar radiation and the
ionosphere cause the phenomena known as auroras.
An aurora (plural: aurorae or auroras) is a natural light display in the sky particularly in the
high latitude (Arctic and Antarctic) regions, caused by the collision of energetic charged
particles with atoms in the high altitude atmosphere (thermosphere). The charged particles
originate in the magnetosphere and solar wind and, on Earth, are directed by the Earth's
magnetic field into the atmosphere.
• There are not enough data about temperature changes
in the thermosphere to determine its upper boundary.
• However, above the ionosphere is the region where
Earth’s atmosphere blends into the almost complete
vacuum of space.
The diagram below shows the different layers of the
atmosphere.
READING CHECK:
What is the lower region of the thermosphere called?
The lower region of the thermosphere is called the
ionosphere.
Temperature Inversions
• Any substance in the atmosphere and that is harmful to
people, animals, plants, or property is called an air
pollutant.
• Today, the main source of air pollution is the burning of
fossil fuels, such as coal and petroleum.
• Certain weather conditions can make air pollution
worse.
• One such condition is a temperature inversion, the
layer of warm air on top of cool air.
• In some areas, topography may make air pollution
even worse by keeping the polluted inversion layer
from dispersing.
• Under conditions in which air cannot circulate up and
away from an area, trapped automobile exhaust can
produce smog, a general term for air pollution that
indicates a combination of smoke and fog.