Earth: Atmosphere

     Today's atmosphere is very different from its prehistoric antecedants. Scientists believe that volcanoes formed the first atmosphere by spewing water vapor, sulfur dioxide, nitrogen, and carbon dioxide into the air. Later primitive aquatic life forms evolved photosynthesis, which created the oxygen atmosphere that exists today. Today's atmosphere extends over 1,100 km above the Earth's surface. It is comprised of many different elements in the gaseous form. The Earth's gravitational field keeps these gases from escaping into space. Nitrogen is the main constituent at 78%, followed by oxygen at 21%. Argon and carbon dioxide make up most of the remaining 1%. Other common molecules include water vapor, hydrogen, ozone, methane, carbon dioxide, helium, neon, krypton, and xenon. The atmospheric composition is similar up to at least 88 km above sea level.
     Scientists divide the atmosphere into four major different layers. From top to bottom, these are the thermosphere, mesosphere, stratosphere, and troposphere. The thermosphere is the hottest of the four with temperatures exceeding 1,000 degrees Celsius. Since it is the first barrier between the surface and outer space, the Sun ionizes this layer. For this reason, the thermosphere is also often referred to as the ionosphere. The ionosphere conducts electricity very well and reflects certain frequency radio waves.
     The second layer, the mesosphere, is the coldest of them all at a height of 50 km to 85 km. Whereas temperature normally decreases with height, the stratosphere has the unique characteristic of higher temperature at a higher elevation. This is due to the presence of the ozone layer found between the stratosphere and mesosphere. Ozone absorbs much of the harmful ultraviolet radiation emitted by the Sun, thus generating much of the heat in the stratosphere. The troposphere extends from the Earth's surface to 8 km at the poles and 16 km at the equator. This layer holds more than half of the total atmosphere. About 380 torr, which is half of standard temperature and pressure, is measured at 5.6 km. The troposphere is warmed mostly by the surface, which is heated by sunlight.
     Although much is already known of Earth's atmosphere, scientists, especially meteorologists, are always looking for new ways to study it, developing many devices like barometers and thermometers.

Aerial Pollution

One major problem facing mankind is aerial pollution from various sources. Of the more prominent, fossil-fuel combustion adds unwanted carbon dioxide to the air. Hydroxyl ions naturally found in the atmosphere help to clean out pollutants, but compounds such as methane still pose a problem. This particular compound has risen 11% since 1978. Chlorofluorocarbons, commonly known as CFC, destroys ozone. Ozone helps protect life on Earth by absorbing much of the very harmful ultraviolet rays from the Sun. Measures have been taken by many countries and independent agencies to reduce not only air but ground and water pollution. For example, the CFC originally found in the first refrigerators have been banned. Unfortunately, much damage has already been done by factories and others. The much-talked-about hole over Antarctica can sometimes be "seen." This hole as seen by satellite images is due to the destruction of ozone in the area.

Copyright © 2000 by Gary Chan and Matthew McDermott. All rights reserved.