The Earth’s atmosphere is composed of 78% nitrogen (N2) and 21% oxygen (O2). Most of the remaining 1% is composed of argon, Water Vapor, and Carbon Dioxide. The force of the Earth’s gravity and the amount of gas cause a sea-level pressure of approximately 14 lbs/ in2 or 1 bar. This pressure decreases rapidly with increasing elevation; that is, at a higher elevation, the amount of gas is less, causing a lower atmospheric pressure. The average temperature near the surface of the Earth is about 60º F. This regulation of temperature is a result of the reflection of incoming solar radiation by the atmosphere coupled with the blanketing effect, caused by carbon dioxide and water vapor. The amount of carbon dioxide in the Earth’s atmosphere is about 0.04% and The water vapor amount varies from 0.1% in cold, dry regions to 3% in warm, wet regions.
Earth Atmosphere Layers
The atmosphere of the Earth is estimated to be about 600 miles thick. However, because there is no set boundary where the atmosphere ends, this estimation is somewhat arbitrary. Nevertheless, the Earth’s atmosphere can be divided into several distinct layers identified using temperature changes, chemical composition, movement, and density.
Earth Atmosphere Layers
The atmosphere of the Earth is estimated to be about 600 miles thick. However, because there is no set boundary where the atmosphere ends, this estimation is somewhat arbitrary. Nevertheless, the Earth’s atmosphere can be divided into several distinct layers identified using temperature changes, chemical composition, movement, and density.
- Troposphere The lowest level of the Earth’s atmosphere is referred to as the troposphere. It contains about 90% of the atmosphere’s mass. Moreover, this layer is characterized by convection currents. These convection currents are generated by the Sun’s radiation heating the ground and lower atmosphere. The warmer air near the surface expands and rises, and is replaced by downdrafts of cooler air from above. Convection currents in the troposphere generate nearly all weather phenomena.
- Stratosphere – The layer of the atmosphere directly above the troposphere is the stratosphere. Ozone Layer is in the upper part of the stratosphere, the Sun’s ultraviolet light creates a layer of ozone through a process called photochemistry. Ozone is a form of oxygen containing three atoms per molecule
- Mesosphere – The atmosphere reaches its coldest temperature of around -170° F in the mesosphere. This is also the layer in which a lot of meteors burn up while entering the Earth's atmosphere.
- Thermosphere – The thermosphere is a region in which temperatures again increase with height. This temperature increase is caused by the absorption of energetic ultraviolet and x-ray radiation from the Sun.
The Earth is heated more near the equator than at the poles. Because of this, the atmosphere redistributes much of the solar energy from warmer regions to cooler ones, which causes the formation of a global atmospheric circulation. This circulation is usually represented in a simplified form, but in actuality, the system is quite complicated. There are many factors that contribute to the complexity of the system, including:
- Landmasses obstructing circulation patterns.
- The tilt of the Earth’s axis causing seasonal variations.
- Coriolis Effect – The Earth’s rotation generates the deflection of large air masses. This phenomenon is known as the Coriolis Effect and is responsible for rotating weather systems such as hurricanes.
The Earth’s atmosphere did not always consist of the same relatively stable mixture of gases that we breathe today. The present atmosphere is the result of very gradual changes that began soon after the Earth formed.
- Primordial Atmosphere – The first atmosphere of the Earth was composed of hydrogen, helium, methane (CH4), ammonia (NH3), water vapor and low amounts of oxygen. This atmosphere was swept away by intense solar winds – vast streams of particles composed primarily of electrons and nuclei of hydrogen and helium emitted by the Sun.
- Secondary Atmosphere – The present atmosphere of the Earth is the result of the release of gases dissolved in molten rock, a process called outgassing (similar to gases observed in present-day volcanic eruptions). The principal components of this “new” atmosphere were probably water vapor, carbon dioxide and nitrogen. However, it did not contain oxygen. The oxygen of the Earth’s atmosphere was slowly added, primarily by green plants through the process of photosynthesis. As the Earth continued to cool, clouds formed and great rains occurred. These torrential rains eventually filled the ocean basins. This event not only diminished the amount of water vapor in the atmosphere, but also carried away most of the carbon dioxide as well. Eventually, large amounts of the carbon dioxide within the oceans were chemically incorporated into carbonate rock.
