THe Atmosphere around you

THe Atmosphere around

you

Guiding Questions

●What is the composition and structure of Earth’s atmosphere?

●How does energy from the sun affect Earth’s atmosphere?

Draw

Draw a line on the image showing how far from Earth’s surface you think the atmosphere extends. What do you notice about the structure of the atmosphere?

Earth’s Insulator

The thin envelope of gases that surrounds the planet, shown in Figure
1, is called the atmosphere. This envelope acts like a coat for Earth.
Just as you wear a coat to protect you from the elements and keep
warm, the atmosphere protects the planet from harmful solar radiation
and keeps the planet’s temperature within a range that allows life to
exist.

The protection our atmosphere provides is “just right.” Too heavy a
coat, and you would be too warm. Too light a coat, and you would be
too cold. Venus and Mars, our planetary neighbors, are good examples
of this. Venus’s thick atmosphere traps heat and smothers the planet,
while Mars’s thin atmosphere retains little heat and results in huge
temperature swings on the planet.

Earth’s atmosphere includes air, water, and energy all connected within
a system. All parts of the system interact with each other to produce the
weather and climate around our planet. The atmosphere also interacts
with Earth’s other systems, such as the biosphere and the ocean, and
its motions are driven by energy from the sun.

Composition of the Atmosphere

The air that makes up the atmosphere is a mixture of various gases, water vapor, and other fine particles. The most abundant gases
found in the atmosphere are nitrogen and oxygen. These two gases account for 99 percent of the atmosphere.

Nitrogen makes up about 78 percent of the air we breathe. Oxygen is essential for animal life and makes up about 21 percent of the
atmosphere’s gases. The remaining 1 percent of the gases in our atmosphere consists of trace, or very small amounts of gases, such
as argon, carbon dioxide, methane, and ozone. Though these gases are far less abundant, they help insulate Earth by trapping solar
energy before it escapes into space. Burning fuels can increase the amount of carbon dioxide in the air.

The atmosphere also contains water vapor, which is the gaseous form of water. The amount of water vapor in the atmosphere varies
from nearly zero percent in the driest deserts to as high as four percent in the extremely humid tropics. Water vapor cannot be seen,
but when it condenses into tiny droplets of liquid water or frozen ice, it forms the clouds we see in the sky. In addition, fine particles of
dust, ash, and other chemicals can be suspended in air. These particles can be seen as smog or smoke when they occur in large
enough amounts, as shown in Figure 2.

Categorize

Options (3)

nitrogen

oxygen

other gases

Organize these options into the right categories

78% of the atmosphere

21% of the atmosphere

1% of the atmosphere

Open Ended

During a volcanic eruption, fine particles of ash spew into the atmosphere. How might suspended particles in the atmosphere affect life on Earth?

Draw

The density of air decreases at higher altitudes because there is less pressure forcing the air molecules together.

There are three circles next to the mountain showing the density of molecules at various altitudes. Near the bottom of the mountain, the molecules in the circle are very densely packed. At mid-level up the mountain, they are more spread out. The circle at the top of the mountain is blank.

Consider the molecules of air at different altitudes. The bottom magnification shows the air molecules near sea level. The center magnification shows the air molecules halfway up the mountain. Draw how you think the air molecules would be arranged at the top of the mountain.

The atmosphere is composed of tiny molecules of gases, water vapor, and particles. Each
molecule exerts a small amount of force when it collides with other particles or a surface. Imagine
the column of air above you that extends all the way into space. This column of air exerts a force
on you called air pressure.

Earth’s gravity pulls the molecules in the atmosphere toward the surface. The weight of the molecules presses down on the molecules
below them. As a result, the molecules closest to the surface of Earth are pressed the most closely together. As you move up through
the atmosphere, the density, or amount of air particles found within a certain volume, decreases. The molecules are more and more
spread out. The distance above sea level is called altitude. The higher the altitude, the lower the air pressure because there is less air
pushing down on you. Air pressure is measured using a barometer (Figure 4).

Gravity is not the only force that affects air pressure. Air pressure is also affected by temperature. When air is warm, heat energy
causes the particles to move more rapidly, forcing the particles around them to spread out. Warm air is less dense than cold air, so it
exerts less pressure.

Multiple Choice

How does altitude affect air pressure?

• Air pressure remains constant regardless of altitude.
• Altitude has no effect on air pressure.
• Air pressure decreases with increasing altitude.
• Air pressure increases with increasing altitude.

Layers of the AtmosphereAs you have learned, the density of air in the atmosphere decreases the

farther up you travel from the surface. In fact, those changes create distinct layers around Earth, which scientists identify based on the
temperature characteristics of each layer. There are four main layers of the atmosphere: the troposphere, the stratosphere, the
mesosphere, and the thermosphere (see Figure 5).

Draw

The atmosphere is divided into different layers by how the temperature (the yellow line in the graph) changes with altitude.

1. Synthesize Information Read each caption. Draw lines to represent the boundary between each layer of the atmosphere. Then connect the atmosphere boxes to the proper space.

Energy in the Atmosphere

The sun provides most of the energy that drives Earth’s systems, including the atmosphere. Solar energy in the form of light travels
through space and reaches Earth. Some is reflected back into space, but most passes through the atmosphere to be trapped by the air
or absorbed as heat at the surface. This energy drives the processes in the atmosphere, such as the water cycle and the movement of
air.

The solar energy absorbed and stored by the atmosphere causes Earth’s surface temperatures to remain relatively stable, or constant.
Recall that the thin atmosphere of Mars causes huge temperatures changes on the planet, and the thick atmosphere of Venus traps so
much heat that the planet is smothered and extremely hot. Earth’s atmosphere is unique because it holds just the right amount of solar
energy to protect life.

Heating of Earth The atmosphere plays an important role in transferring heat to and from

Earth’s surface. Heat is transferred in three ways: convection, conduction, and radiation.

Energy from the sun warms Earth’s atmosphere as it reaches its surface by radiation. Some of the energy that
hits Earth’s surface is absorbed by land or water, some is reflected back into space, and some warms the air
that touches Earth’s surface through conduction.

Convection currents are also always moving Earth’s air and water to redistribute heat to and from cool and
warm places. This constant transfer of energy in the atmosphere and hydrosphere is responsible for the
movement and cycling of air and water around Earth.

WindsAs the air in the atmosphere is heated by solar energy and Earth’s

surface, the unequal heating causes changes in air pressure. Warm air expands and
becomes less dense. Cool, dense air nearby pushes in underneath, causing the
warmer air to rise. This movement of air parallel to Earth’s surface is called wind. Air
moves as wind from areas of higher pressure to areas of lower pressure.

Unequal heating over small areas results in local winds, which are winds that blow
over short distances. Two examples of local winds seen along shorelines are sea
breezes and land breezes. Unequal heating causes sea breezes to occur during the
day, when the land heats up faster than the water. Through conduction, the land
heats up the air above it, causing the air to expand and rise. The cooler air over the
water moves into the low-pressure area over the land. At night, the reverse happens
and land breezes occur. The land cools off faster than the water and the cool, dense
air blows from the land to the water, where the air pressure is lower.

Global winds, shown in Figure 6, are also caused by unequal heating, but they occur
over much larger areas. As solar energy warms the areas near the equator, cold air
near the poles moves in global winds to areas of low pressure. Convection currents
caused by cool and warm air produce global winds.

Multiple Choice

Why is the atmosphere heated unequally by the Sun?

• solar energy hits some areas more directly because of the Earth's tilt

• The atmosphere is heated equally by the Sun, there is no unequal heating.
• Due to the Earth's flat shape causing varying angles of sunlight incidence at different latitudes.
• Because the Sun emits different temperatures of light at different times of the day.

Open Ended

Why is the atmosphere heated unequally by the sun?