Water and Weather
Chapter Five: Earth’s Atmosphere
• 5.1 The Atmosphere
• 5.2 Layers of the Atmosphere
• 5.3 Earth is Just Right
Investigation 5A
The Atmosphere
• Can you measure atmospheric pressure?
5.1 The Atmosphere
• Earth’s atmosphere is
a layer of gases
surrounding the planet
that protects and
supports life.
• The air we breathe in
our atmosphere is
made of a mixture of
gases.
5.1 What's in Earth's atmosphere?
• Earth’s atmosphere contains 2 main gases,
nitrogen and oxygen, and several trace gases.
• Oxygen, the second most
abundant gas, makes up 21% of
Earth’s atmosphere. Oxygen is
added to our atmosphere through
photosynthesis.
• Trace gases include argon at
0.93% and carbon dioxide (CO2)
at 0.04%. We exhale CO2 when
we breathe.
5.1 Nitrogen Cycle
• Nitrogen is the most
abundant gas in Earth’s
atmosphere. It makes up
about 78% of all air
molecules.
• Nitrogen is essential to
protein production. Protein is
found in the body tissues of
all living things. Plants use
nitrogen in the soil to make
those essential proteins.
5.1 The story of Earth’s
atmosphere
• Earth’s unique
atmosphere exists
because our planet
has the right balance
between mass and
distance from the
Sun.
5.1 Pressure in
the atmosphere
• The gas molecules closest to
Earth’s surface are densely
packed together because the
molecules above them are
pushing on them.
• The higher up you go into the
atmosphere, the lower the
pressure, because there are
fewer molecules pressing
down.
5.1 Pressure changes with
altitude
• Altitude measures how high
something is above sea level. The
higher the altitude, the fewer air
molecules there are.
5.1 Pressure in the atmosphere
• At sea level, the weight of the
column of air above a person is
about 9,800 newtons (2,200
pounds)! This is equal to the
weight of a small car.
• Our bodies are best suited
for atmospheric pressure at
sea level because our
bodies exert an equal and
opposite pressure outward.
5.1 Measuring Pressure
• A barometer is an
instrument that
measures atmospheric
pressure.
• Long ago, mercury
barometers were used.
5.1 Measuring Pressure
• Since mercury is a
poisonous liquid,
aneroid barometers
are used today.