The document discusses the composition and evolution of Earth's atmosphere. It notes that nitrogen makes up 78% of the atmosphere, while oxygen is 21% and other gases like argon and carbon dioxide make up the remaining 1%. Earth originally had an atmosphere of hydrogen and helium that eventually escaped. Later, volcanoes released water vapor, carbon dioxide, and ammonia, forming a second atmosphere. Cyanobacteria introduced oxygen to the atmosphere between 3.3 to 2.2 billion years ago. The modern atmosphere of nitrogen and oxygen is considered the third atmosphere and has a composition influenced by biological and geological processes.

2. Chapter 4
The Earth’s
Atmosphere

3. COMPOSITION OF THE
ATMOSPHERE
The atmosphere is a
mixture of different
gases, oxygen, and
nitrogen. Of these,
nitrogen is the most
abundant. It accounts
for 78% of the total
volume of the air while oxygen makes up 21%.
The remaining 1% is mostly argon and carbon
dioxide.

5. EVOLUTION OF
EARTH’S
ATMOSPHERE

6. The gases of the atmosphere most important
to man – nitrogen, oxygen, carbon dioxide,
and water vapour, are rare in the universe.
The modern atmosphere is sometimes
referred to as Earth’s “third atmosphere”,
in order to to distinguish the current
chemical composition from two notable
different previous compositions

7. The elements Hydrogen H and Helium He
are the primarily chemical composition of
the original atmosphere. Earth’s original
atmosphere was probably just
hydrogen and helium, because these
were the main gases in the dusty,
gassy disk around the Sun from which
the planets formed.

8. The Earth and
its atmosphere
were very hot.
Molecules of
hydrogen and
helium move
really fast,
especially
when warm. Actually, they moved so fast
they eventually all escaped Earth's gravity
and drifted off into space.

9. Earth’s “second atmosphere” came from
Earth itself. There were lots of volcanoes,
many more than today, because Earth’s
crust was still forming. The volcanoes
released
1.steam (H2O, with two hydrogen atoms
and one oxygen atom),
2.carbon dioxide (CO2, with one carbon
atoms and two oxygen atoms),
3.ammonia (NH3, with one nitrogen
atom and three hydrogen atoms).

12. CYANOBACTERIA- the bacteria shaped like
these existed approximately 3.3 billion years
ago and was the first oxygen producing
evolving phototropic organisms. During the
period of 2.7 to 2.2 billion years ago they were
conversion of the earth’s atmosphere from
ANOXIC STATE (from state without oxygen) to
OXIC STATE (a state with oxygen)

13. Photosynthesizing plants later evolved
and continued releasing oxygen and
sequestering carbon dioxide.
Bacteria would also convert to ammonia
into nitrogen. But most of the nitrogen
currently present in the atmosphere
results from sunlight-powered photolysis
of ammonia released steadily over the
aeons from volcanoes.

14. OXYGEN-NITROGEN atmosphere is the
“third atmosphere”.
Between 200 and 250 million years ago,
up to 35% of the atmosphere was oxygen.
The modern atmosphere has a
composition which is enforced by ocean
blue green algae aw well as geological
processes.

15. THE ATMOSPHERE IS VERY
IMPORTANT BECAUSE;
1. All living organism needs this vapor
or gas if they are continue living.
2. Air is escaping in the outer atmosphere
and it constantly being replaced by the
Earth’s crust. The amount of air in the
atmosphere don’t change much in its
ratio, as a result all living organisms
that depends in it for living also change
slowly, if there is a sudden change in
the atmosphere life would change with
it

16.  Conduction – collision
from one molecule to
another with heat
from one with higher
temperature to a
lower temperature .
 Convection – movement
of a mass or substances
from one place to another.
Radiation – energy
moves through a material
without the aid of the material

17. ATMOSPHERE CIRCULATION
Cold – compresses air particles
Heat – expands air particles

18. EFFECT PRESSURE
As air close to the earth is heated, the gas
molecules move father and farther apart
and air is lighter. The lighter, warmer air
rises. The heavier, cooler air above moves
down forward the surface of the earth
AIR PRESSURE
Because air has weight, it presses on all
objects it touches. Air pressure is a
controlled by the temperature of the air,
the amount of vapor in the air, and the
altitude.

19. 1. As air particles are
compressed, pressure
between particles is
increase temperature
is decreased (air cool).
2. As air particles
expand, pressure is
decreased between
parties, temperature
is increased (air warms).

20. Warm air is lighter than cold air and
therefore, has less pressure than cold
air. An increase in pressure can be
caused by a decrease in temperature.
EFFECTS ON WEIGHT OF
PARTICLES
1. Warm air –
molecule expands,
becomes lighter
and rises up to sky.

21. 2. Cool air – molecules are
compressed, are heavier, and
goes down the surface of the
earth.