The Atmosphere
The atmosphere is what you might call the sky. Its everywhere around you, and contains the air you breathe, with all the other gasses pulled in by earth’s gravity. It reaches over 560 km from the earth, or 348 miles from the earth. Scientifically, it’s mapped into different layers, from the ground level to hundreds of kilometres toward the sky. These layers don’t have specific boundaries, but fade into each other like any other natural mapped area. These areas have different properties, which is why they were categorized differently. The height of the atmosphere is called the altitude.
The whole atmosphere contains many different gasses. 78% of the atmosphere is taken up by nitrogen, found regularly around the air. Oxygen takes up 21%, increased by photosynthesis of plants. Other gasses, including argon, helium, methane, neon, krypton, hydrogen, nitrous oxide, and xenon are found in the atmosphere, but only add up to the remaining 1% of the atmosphere.
Although many people do not think about it, the atmosphere was not made when the earth was formed, or even when the earth was cooling. The numerous volcanoes found on the surface of “young earth’ released inner pressures of trace gasses like ammonia, carbon dioxide, carbon monoxide, methane, sulphur dioxide and some hydrogen. Water vapour also escaped from the volcanoes. These gasses were held in by earth’s atmosphere. Oceans were formed, (mostly by condensation of water vapour) and some people think this is how life evolved. Many types of gasses which are not in the atmosphere today have dissolved in the oceans. Various gasses were also drawn in from space. Three and a half billion years ago, basic forms of life (especially photosynthesis of algae and small plants) gave a continuing oxygen supply, kept the oxygen cycle going, and increased oxygen levels in the atmosphere. The spread of these plants exponentially increased the oxygen supplies, until what we have today. Decay of natural radioactive materials released gasses like argon (today makes 1% of the atmosphere) and xenon into the air. 400 million years ago, the atmosphere looked basically the same as it does today (scientifically), except since the 1800’s, various human actions have released carbon dioxide to 125% of its pre-fossil fuel amount. Carbon dioxide still takes up less than 1% of the atmosphere, mostly near the ozone layer. The atmosphere has been through a long but very uneventful history.
The surface of the air is the central line between the insides of the earth and the atmosphere. It is just under the troposphere, and contains gasses within plants, animals, etc. The middle of the surface is called the sea level, and is where the ocean surface, without waves, would lie. Mountains and low lands change the altitude and depth of the surface, like Mount. Everest which is 8.85 km above sea level, and the shore of the dead sea, between Israel and Jordan, which is 0.4 km below sea level. The temperature, with the effects of weather, ranges from 135.9F to -128.6F.
The troposphere is the lowest part of the atmosphere, besides the surface. The troposphere extends from 8 to 14.5 km above sea level, or 5-10 miles above sea-level, although the start of the troposphere varies in different regions. Over the poles, the troposphere starts at 6 miles above, and at the equator, the troposphere starts at 10 miles above. Its pressure is the densest because it’s the closest to the surface, and contains the majority of all gasses found in the atmosphere. All weather happens in the troposphere. Clouds condense, rain falls, and snow is created here. The temperature, because of the weather, ranges in this region from 17 to -52C, although the outside temperature decreases 3.5 every 1,000 feet up in the air. All commercial planes fly at this altitude or lower, and hot air balloons also float near the bottom of the troposphere. Non-scientists normally call this whole section the “lower atmosphere”.
The stratosphere is another section of the atmosphere. It melds from the top of the troposphere and starts thickly at 16 km high or 10 miles high, and extends upward to 50 km or 31 miles above sea level. It is 35 km thick, or approximately 22 miles thick. This area is drier, and less dense than the troposphere. Meteorological balloons are found here. Humans may have difficulty breathing in the stratosphere unaided because of the low air pressures. Although the gasses here are very sparse, the stratosphere has a lot more air than any of the atmosphere above it. In fact, 99.99% of all the “air” in the atmosphere is contained within the stratosphere and the troposphere. The temperature in the stratosphere is an average of -3C, or 28F, warmed by the absorption of ultraviolet rays from the sun. The stratosphere is also warmer than the troposphere because the “ozone layer” is in the bottom half of this section (16-31 km high, or 10-20 miles high), and most of the air pollution found (including CO2 and methane) is also in this section. The ozone layer blocks off harmful ultraviolet radiation, which can contribute to the warmer temperature.
The mesosphere fades in from the top of the stratosphere. It is 50-80 km high, or 30-50 miles high. It is the “middle” of the atmosphere, (the prefix “meso” means middle in Greek) as the lower and upper atmospheres are under or over it respectively, but the stratosphere is also included in the classification of “middle atmosphere”. The temperature in the mesosphere is -100C, being the coldest part of the atmosphere. This is because the troposphere is warmed by weather, reflections of the sun’s rays, the stratosphere is warmed by the ozone layer and the thermosphere (the area above the mesosphere) is warmed by the sun’s radiation. The mesosphere can be the “dividing line of the temperatures”, as both the upper and lower atmosphere is warmer. Also, it can be called the middle because it is an area of the atmosphere that is at the maximum altitude of research planes, and the minimum altitude of spacecraft. Therefore, it has been rarely studied, and so the least understood area of the atmosphere. Jokingly, to research personnel, the mesosphere is sometimes called the “ignorosphere” because they don’t know much about it. Meteors start burning up in this atmospheric layer, and, because of the cold temperature, frozen water vapour creates noctilucent clouds (NLC’s), or ice clouds. They may be visible when the sun’s rays shine on them.
The thermosphere is found right above the mesosphere. It stretches 80-300 km high, or 50-200 miles high. The lower parts of the thermosphere have oxygen molecules broken down into atoms, with hydrogen and helium found elsewhere in the ionosphere. The temperature, in sunlight, hovers around 600C, or 11,000F at 178 km, or 120 miles high. This is because the thermosphere is exposed to the sun’s radiation, which heats it up considerably. During solar storms, a type of sun storm radiation phenomenon, the thermosphere is exposed to an incredible amount of radiation, and may reach the temperature of 2000C, or 3600F. The name thermosphere was made because this was a largely hot layer of the atmosphere.
The ionosphere contains the thermosphere within its lower half, sharing some of its properties. In the ionosphere, radio waves from earth are reflected back to the surface, space shuttles have just lost their rocket boosters, and rockets start releasing their payload. The main useful difference between the ionosphere and thermosphere is that the atoms in the ionosphere are struck by space radiation, which ionizes them, or charges them electrically. This is useful for radio wave transmitting items, which would reflect off the ionized atoms.
The exosphere is the last part of the atmosphere. It starts at 480 km high and ends at approximately 960 km high. It is also the largest layer (in terms of area), being 480 km high, and the same size as all of the atmospheric layers below it. Although it is big, the exosphere has almost no air pressure at all. Satellites and other types of spacecraft orbit the earth in this zone, with very little or no air resistance because of the sparse air. Atmospheric tides push through the exosphere, and change directions every 6 hours. Auroras, including the Aurora Borealis and the Aurora Australis (the northern and southern lights that appear in the night sky in the north and south poles respectively) occur in this area too. They are made when charged solar particles strike the earth’s magnetic field. The particles (on impact) release light energy, which produces the light in the auroras. Since the poles of our magnetic field are the strongest point, the particles are drawn toward the poles and collide in a ring at different times, creating this natural phenomenon. Some particles in the exosphere move at incredibly high speeds, and escape the earth’s gravitational pull. This way, earth is slowly losing its atmosphere (but man-made and natural chemicals escaping in the air make up for it), but this process will take over a couple of billions of years. The root word of exosphere, “exo”, means outside, as the exosphere is the outside of the atmosphere. The area from the ionosphere to the exosphere is called the upper atmosphere.
The atmosphere of earth is very big, and contains many different parts. Each part was separated because of their distinct quality, but together, they form the atmosphere that we live and breathe in.
