Chapter 4The Earth’s 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.

COMPOSITION OF THE ATMOSPHERE

EVOLUTION OF EARTH’S ATMOSPHER

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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

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.

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.

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).

ONE OF THE EARLIEST TYPE OF BACTERIA

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)

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.

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.

THE ATMOSPHERE IS VERY IMPORTANT BECAUSE;

1. All living organism needs this vaporor 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

MECHANISM OF HEAT TRANSFER Conduction – collisionfrom one molecule toanother with heatfrom one with highertemperature to alower temperature .

Convection – movementof a mass or substancesfrom one place to another.

Radiation – energymoves through a materialwithout the aid of the material

ATMOSPHERE CIRCULATIONCold – compresses air particles

Heat – expands air particles

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.

1. As air particles arecompressed, pressurebetween particles isincrease temperatureis decreased (air cool).

2. As air particlesexpand, pressure isdecreased betweenparties, temperatureis increased (air warms).

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

PARTICLES1. Warm air – molecule expands, becomes lighter and rises up to sky.

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