Connecting People with Nature

Air and the Atmosphere

Essential Knowledge for Naturalists

Without air, Earth is just a Rock

The Earth has an atmosphere made up of gases and water vapor. This thin veil of air extends approximately 60 miles from the surface, and contains a mixture of oxygen, carbon dioxide, nitrogen, inert gases and other components. Most of the atmosphere is nitrogen, about 80%. Oxygen, the component of the Earth's atmosphere that humans need to breathe, makes up a little over 20% of the atmosphere. Carbon dioxide, used by plants in their energy cycle, makes up less than one half of one percent of the atmosphere, but is increasing in proportion due to human causes, such as automobile exhausts, and power plant emissions. The atmosphere exerts downward pressure on us of about 14.7 pounds per square inch all the time.

The atmosphere protects the surface of the Earth from harmful radiation by filtering it out before the suns rays reach the Earth. The insulation of the atmosphere also keeps temperatures in the range that allows for human and other life on Earth. Without the atmosphere, not only would we suffocate due to lack of oxygen, we would blister during the day and freeze solid during the night.

Layers of the Atmosphere

The all-important atmosphere is not homogeneous. There are five distinct layers within the atmosphere.

The troposphere is the layer nearest the Earth. This layer contains most of the air and water vapor of the atmosphere, and is the zone where life happens. Our weather is generally within the troposphere as well. The layer extends about 3 to 7 miles from the Earth's surface. It is thinner near the poles, and thickest near the equator.

The stratosphere, the next layer of the atmosphere, extends from the troposphere out approximately another 20 miles. This layer is fairly calm and has very little air movement or air currents. In fact the stratosphere is stratified. That is, there are layers within this layer. Air near the top of the stratosphere is warmer, while air in the lower stratosphere is cooler.

Above the stratosphere is the mesosphere, the middle layer of the atmosphere. Here, the air gets cooler the further it is from Earth. This layer is about 20 miles thick, and is above the range of most life, beyond those who can afford to fly in rockets or space-planes. Not much is known about this layer of the atmosphere.

The thermosphere is the next layer of Earth's atmosphere. Temperatures in this aptly-named layer can reach 4,000 degrees Fahrenheit during the day. The thermosphere is about 160 miles thick, and is the source of the northern lights.

The exosphere us the final layer of the atmosphere. It contains the lightest gas particles found in the atmosphere, such as helium and hydrogen. The exosphere extends perhaps 4,500 miles into space. Beyond the exosphere, in fact, you are in outer space.

Weather & Climate

Simply defined, weather is everything that naturally happens in the atmosphere. It includes the temperature, winds, and precipitation. Temperature both influences, and is influenced by, winds and wind currents.

As the sun heats the Earth's surface, the air above the Earth is also heated. Hot air, because it expands, also rises, while cooler air gets denser as it gives off energy and sinks. This rising and falling causes a change in pressure, with cooler areas becoming high pressure, and warmer areas having lower air pressure. These pressure differentials then cause air movement, or wind. The spin of the earth then comes into play, because as the planet spins, the air does too. In the northern hemisphere, prevailing winds are from the west. So, if you want to find out what the weather in your area will be like, find out what is going on west of you, and soon enough, you will feel the effects.

As winds flow around the Earth, they shift the temperature from the poles and the tropics. When winds flow over water, often they accumulate evaporated moisture, which forms clouds. Clouds, of course, eventually bring rain, snow, or other precipitation. The amount of precipitation is of course, a major factor in the types of plant and animal life found in an area, along with the temperature.

The weather patterns of a region over a long period of time create the climate of that area. Climate is a key factor in determining the ecological communities that can be found in an area. You can see then, that the atmosphere, weather and plant and animal life, and therefore, humans, are all intimately intertwined, creating just the right conditions for the diversity of life to flourish here.'s feed chicklet's email chicklet's e-newsletter chicklet
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