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The Atmosphere

The climate of a planet is dependent how far it is from the sun, its mass and the composition of its atmosphere. Out of the earth’s atmosphere, 78% is nitrogen, 21% is oxygen while other gases account for only 1%. The water vapor content in the atmosphere varies from 0 to 2% while carbon dioxide accounts for 0.03-0.04%. Some of the minor gases in the atmosphere such as carbon dioxide absorb thermal radiation escaping from the earth to outer space. They act as a blanket keeping the earth warmer by preventing the radiation from escaping. They are thus called greenhouse gases as they function as greenhouses, maintaining warm temperatures. The gases are responsible for the greenhouse effect experienced over earth. Greenhouse gases are very important to the earth, as the temperatures on earth would drop to about -20°C if the gases were not there.

The atmosphere consists of layers of gas and solid particles floating above the earth surface. It extends many miles from the surface of the earth. They are held around the earth by earth’s gravitational pull. However, they thin out as you move further from the earth surface.

The atmosphere has several layers and is responsible for life on earth. It helps contain the air we breathe, making life possible. It also protects us from harmful substances from outer space. It holds gases, moisture and other particles that help make life on earth bearable. It is the shield that protects us and sustains life.

The transfer of energy between the atmosphere and the earth surface is through conduction, convection, and radiation. Movements in currents also influence the transfer of heat on the earth surface. Ocean currents are a significant factor in the formation of weather phenomena on earth. They transfer heat to the poles, which then affect the weather.

The Atmospheric Gases

Four of the gases forming the atmosphere account for 99.998%. Nitrogen is the most common of all the gases in the atmosphere. It plays a major role on earth as it neutralizes oxygen and prevents instantaneous combustion on earth. Oxygen, the second most common gas, is responsible for sustaining life. It essential for respiration in all living things. It also facilitates combustion, as it aids the burning process.

Carbon dioxide is another gas that is critical for life on earth. Plants need it for photosynthesis, a process that produces oxygen as a byproduct. The respiration in plants and animals helps keep the balance between oxygen and carbon dioxide on earth.

The other minor gases in the atmosphere play different roles. They are also useful in different ways. For example, Argon is used to preserve documents among other uses.

The composition of the atmosphere varies depending on the presence of water vapor. Often, water vapor constitutes up to 4% of the atmospheric composition. Thus, the composition of the other gases would be lower than they are in a completely dry atmosphere. There are instances, such as above deserts, where the water vapor in the atmosphere would be zero.

During hot humid days, water vapor content in the atmosphere can rise to 3%. It gets to the upper limit of 4% around the tropics.

The Layers of the Atmosphere

The atmosphere consists of four layers, based on temperature. The four layers include the thermosphere, mesosphere, stratosphere, and troposphere. Beyond the thermosphere, we have the exosphere, which merges into outer space.

The Troposphere

The first layer from the earth surface is the troposphere. It accounts for 70-80% of the atmosphere and reaches up to 4-12 miles (6-20 km) off the surface of the earth. It is the layer that supports life and most of the weather phenomena occurs here. The troposphere contains 99% of the atmospheric water vapor. As you go higher, the gases decrease and the air becomes thinner. The temperature also decreases with height above earth surface. That is because the gases that hold back earth’s radiation are lower and higher in the troposphere the air is too thin to hold heat. The temperatures drop from 62°F (17°C) to as low as -60°F (-51°C) as you go higher. The region experiences most of the weather phenomena on earth.

The position from the equator or the poles affects how far the troposphere extends into space. It is about 11-12 miles (18-20 km) high at the equator, while it is under four miles high at the poles. The peaks of the highest mountains on earth are, however, still within the troposphere. After the troposphere, you get into the tropopause, which is the transition between the troposphere into the stratosphere. Together with the tropopause, the troposphere is called the lower atmosphere.

The Stratosphere

The stratosphere starts from where the troposphere ends. It extends to 31 miles off the earth surface. The layer accounts for 19 percent of the atmospheric gases. However, it has very little water vapor. In the stratosphere, there is a layer called ozone. It is formed by the dissociation of oxygen molecules into individual oxygen atoms. The oxygen atoms then combine with oxygen molecules (O2) to form ozone, which is a molecule of oxygen that is made up of three atoms of oxygen (O3). The conversion of oxygen molecules into ozone is possible because of the incoming solar radiation, which is at wavelengths below 240 nm. At an altitude of 25 km (16 miles), ozone gets to its peak density, which is just a few parts per million.

The ozone is a thin gas forming a protective layer above the earth surface. Given the thinness of ozone, it would amount to about 3 millimeters thick if compressed to one layer on the surface of the high altitudes, ozone becomes increasingly rarefied. At around 80 km (50 miles) off the earth surface, free ozone electrons exist for short periods because of the thinness of the gas at such heights. The free electrons easily fuse with nearby positive ions. These charged particles mark the beginning of the ionosphere. The ionosphere has the properties of both a gas and a plasma.

In the stratosphere, temperature increases with height. That is because oxygen molecules that form the ozone layer increasingly absorb radiation. The ozone is critical to earth as it absorbs harmful ultraviolet rays from the sun. It thus offers a shield of protection to earth. The Ozone layer starts about 20 km above the earth surface to about 60 km. The temperatures rise from around -76°F (-60°C) at the start of the stratosphere to about 5°F (-15°C) at the stratopause. That is because of the absorption of ultraviolet radiation. The layer is mainly calm as the gases are slow due to the increasing temperature. After the stratosphere, you move into the stratopause, which transitions the stratosphere into the mesosphere.

The stratosphere is stable. Thus, most jet aircrafts fly in this layer.

The Mesosphere

The mesosphere starts at the stratopause and extends to 53 miles (85 km) above the surface of the earth. The gases continue to thin as you go higher. Oxygen molecules become very sparse. As a result, the warming effect of ultraviolet radiation decreases as you move higher, leading to a drop in temperature. Temperatures decrease from about 5°F (-15°C) to as low as -184°F (-120°C) at the end of this layer. Although the gases thin with height above earth surface, the mesosphere gases are able to slow down meteorites breaking into the atmosphere. The meteorites burn up on entry into the atmosphere, leaving spectacular fiery trails in the sky at night.

The Thermosphere

The thermosphere forms the upper atmosphere. It starts from the mesopause and stretches to 430 miles (690 km) above the surface of the earth. The air in this layer is very thin, with the gases scantier. In this layer, the only energy absorbed is the sun’s ultraviolet and x-ray radiation, which is at high energy. That is because of the decrease in gases in this layer. The temperatures in this layer increase with height from earth surface. The temperatures can reach highs of 3,600°F (2000°C) near the end of the thermosphere. However, the extremely thin air in this layer would still make it feel very cold on the human skin. The energy from the molecules in this layer (which are few) would still not be sufficient to heat our skin. The thermosphere ends at the thermopause, from which the exosphere starts.

The Exosphere

The Exosphere is the furthest layer of the atmosphere. It starts from the thermopause to about 6200 miles (10,000 km) from the earth surface. The layer merges into outer space and the atoms and molecules in this layer escape into space. The satellites that orbit the earth are also in this layer.

The Ozone Hole

The Ozone Hole, a result of ozone depletion, increases in size during the months of September and October due to weather movements and currents towards the poles.