The Atmosphere

The earth is surrounded by layers of gases, our atmosphere. They are kept near the earth’s surface by gravity.

Our atmosphere filters the sunlight and keeps dangerous rays from reaching our planet. Without such a filter it would get too hot during the daytime. At night itprevents heat from escaping so it does not get too cold.

Without an atmosphere life on our planet would not be possible. It also makes our world a more pleasant place to live. Air carries sound waves, which let us hear voices or listen to music. The atmosphere creates rainbows, makes the sky turn blue on clear days and the sun red when it sets

The makeup of our atmosphere

The air near the earth’s surface consists of 77 percent nitrogen and about 21 percent oxygen. Carbon dioxide is also present, but only in small amounts. Nevertheless it is very important because green plants use it when they make their food. Higher up you can find helium and hydrogen in the atmosphere.

Not all gases are created by nature, some are produced by people. Methane rises into the atmosphere from decaying plants and animals. Carbon monoxide and chlorofluorocarbons (CFCs) enter the atmosphere because of industrial activities.

Weight and Pressure

We often think that the air is weightless but it isn’t. The whole weight of the earth’s atmosphere is about 5.5 quadrillion tons (55 followed by 14 zeros). Air is heaviest at sea level because the air molecules are pressed together. It also presses against our bodies but we have pressure inside , so we don’t feel it. When you move farther away from the earth’s surface the atmosphere gets lighter and lighter because there is more room between air molecules. The weight of the air decreases and so does air pressure.

Layers of the atmosphere

Troposphere

The troposphere is the layer closest to the earth’s surface and the part of the atmosphere that we know about best. It extends from sea level to almost 19 km above the equator, but only 9 km above the North and South Poles. In the troposphere it gets colder the higher up you move. Temperatures drop by about 0.7°C to 1 ° C every 100 meters.

This lower part of the atmosphere is responsible for our weather. Waterevaporates from oceans and rivers and forms clouds which can produce, rain or snow. Winds also get stronger the higher you go up. At the top of the troposphere so-called jet streams reach speeds of up to 300 km an hour.

As you go up the air gets thinner. People must wear pressure suits and use oxygen masks when they travel to higher regions. The troposphere helps to keep the temperatures on earth moderate.

Stratosphere

The second layer of our atmosphere is the stratosphere. It extends up to an altitude of 50 km above the earth’s surface. A gas calledozone causes the temperature to rise again. Ozone absorbs the ultraviolet light that comes from the sun and changes it into heat. Without ozone this dangerous light would reach the earth’s surface , cause skin problems and harm plants and animals.

Mesosphere

The mesosphere extends from the top of the stratosphere to about 80 km. The air becomes even thinner and the temperatures dropagain. At the top of the mesosphere they may be lower than -75° C.

Thermosphere

The thermosphere ranges from 80 km to about 400 km above the earth. In this layer temperatures increase rapidly with altitude. At the bottom temperatures are below freezing, at the top they can reach over 1,000 °C. Satellites orbit the earth at this height.

Exosphere

In the outermost layer of the atmosphere temperatures are steady, averaging around 1200°C. Molecules in the exosphere are so far away from each other that they normally don’t collide. The layer extends into outer space and joins with the atmosphere of the sun and other planets. Atoms and particles escape the earth’s gravitation and float to outer space.

Layers of the Atmosphere

Endangered atmosphere

During millions of years the atmosphere has remained the same. It can change when, for example, when ashes and hot gases erupt from an active volcano. This can block sunlight for years or cause temperatures to change.

In the past centuries people have also caused great changes in the atmosphere.

• More and more grazing animals produce methane gas.

• Fossil fuels like coal, oil or gas produce carbon dioxide which leads to thegreenhouse effect. This gas makes the atmosphere denser and it traps the heat.

• CFCs that come from air conditioning, spray cans or burning plastic get into the atmosphere and endanger the ozone layer.

• Sulfur dioxide and nitrogen oxide are emitted into the atmosphere by industries and cars. These gases can combine with water in the air and produce what is called acid rain. It pollutes lakes anddamages buildings and other structures.

The greenhouse effect

Words

• absorb = to take in
• acid rain = rain that has chemicals in it and can damage the world around us
• activity = thing that you do
• air pressure =how heavy the air is
• altitude =how high an object is above sea level
• amount =quantity
• average =usual, normal
• block = keep out
• carbon dioxide = gas that is produced when we breathe out or when carbon is burned
• carbon monoxide =a posionous gas that is produced when you burn fuel or wood
• cause =lead to
• century = a hundred years
• chlorofluorocarbon =a gas that damages the ozone layer; it is in refridgerators an spray cans
• collide = to crash into each other
• combine = to get together with
• consist = is made up of
• create = make
• damage =destroy, harm
• decay =to be slowly destroyed in a natural, chemical way
• decrease = to go down
• deforestation = the cutting and burning down of trees in a place
• dense =many objects that are close together, in a small area
• drop = go down
• edge =border; the part that is farthest away from the centre
• emit = to send out
• endanger =to put into danger
• engine = a machine that produces power so that a car can move
• equator = a line around the middle of the earth that divides it into two halves
• erupt = to break out with a lot of power
• escape = to get away from; to get out of
• evaporate = to change slowly into gas
• extend = to go from one place to another
• farther =beyond
• filter = to let certain things in and keep other things out
• float = to move slowly
• fossil fuel = energy like coal or oil that is produced by dead animals and plants in millions of years
• gravitation =the power that makes two objects move towards each other
• gravity = the power that makes things fall down to earth
• graze = to eat grass in the fields
• greenhouse gas =a gas , like carbon dioxide or methane that makes the atmosphere thicker and does not let heat out of it
• harm = endanger
• heat = warmth
• height =how high something is
• helium = gas that is lighter than air and is used to make balloons float
• hydrogen = the lightest of all gases
• increase = to go up
• jet stream = very strong winds at the top of the troposphere
• join = to get together with
• layer =somehting that is between two other objects
• methane = a gas that you cannot smell or see; it can be burned to give heat
• moderate = not too hot and not too cold
• nevertheless =yet, but
• nitrogen = a gas that has no colour or smell
• nitrogen oxide =when you combine nitrogen and oxygen
• orbit = to go around a planet or the sun
• outermost = furthest from the middle
• oxygen = a gas that is in the air and that we need to breathe
• oxygen mask = mask you put on if there is not enough air around you to breathe
• particle = a very small piece of something
• pleasant = nice
• pollute = to make dirty so that we cannot use it
• pressure suit =a special suit you must wear to survive when you fly at great heights
• prevent =keep from doing something
• radiation =a form of energy that comes from nuclear power; it is dangers to living things
• range = to go from … to ….
• rapidly = fast
• ray = a line of light
• reflect =send back
• remain = stay
• responsible =to cause something
• rise = to go up
• sea level =the normal height of the sea; you use it as a standard for measuring other heights
• set = to go down
• speed =how fast something is
• spray can =can from which you can spray paint onto things
• steady = always the same, does not change
• sulphur dioxide = a gas that is very poisonous
• surface =the top part of an object
• surrounded = something is on every side
• trap = if you do not let something out ; it cannot escape
• ultraviolet light = light that you cannot see but it makes your skin darker when you are in the sun
• weight =how heavy something is
• weightless = without weight