Atmosphere

The atmosphere is the blanket of gases that surround the Earth. That blanket of gases is mostly the air we breathe.

The atmosphere protects the Earth from the intense heat of the Sun during the day and the freezing cold of outer space at night. The atmosphere insulates the Earth and makes it habitable for plant and animal life.

The atmosphere can not be seen from Earth, but it can be seen from space. Look at a photograph of Earth from space. You will see the Earth’s oceans and landmasses, you will see white clouds, and above the clouds but below the blackness of outer space, you see a blue haze. That blue haze is the atmosphere.

The atmosphere stretches from the surface of the Earth to 6,200 miles above the Earth where it merges with outer space. The atmosphere consists of five layers. Here are the five layers of the atmosphere:

• Troposphere is the layer closest to Earth. The troposphere extends from the Earth’s surface to about 7 miles (12 km) above the Earth. Weather happens in the troposphere.
• Stratosphere is just above the troposphere; it extends from 7 miles to 31 miles (12-50 km) above the Earth; airplanes cruise in the lower part of the stratosphere.
• Mesosphere is above the stratosphere; it extends 31 to 50 miles (50-80 km) above the Earth; the air is so thick in the mesosphere that meteors slow and burn up in the mesosphere; the bright trails of meteors burning up in the mesosphere are called shooting stars.
• Thermosphere is above the mesosphere; it extends from 50 to 440 miles (80-700 km) above the Earth; satellites orbit in the thermosphere; gas molecules in the thermosphere can heat to 3600°F (2000°C), but the molecules are so far apart the thermosphere feels cold.
• Exosphere is above the thermosphere; it extends 440 to 6,200 miles (700-10,000 km) above the Earth; gas atoms and molecules are so far apart in the exosphere that they can travel for hundreds of miles without running into one another. The temperature in the exosphere is absolute zero. The top of the exosphere is where the Earth’s atmosphere merges with outer space.

The part of the atmosphere that we are most familiar with is the troposphere. The troposphere is closest to Earth and that is where weather occurs. Sun rays heat the land and oceans and the air closest to the Earth’s surface; as a result, warm air rises, especially at the Equator. As the warm air rises, colder air flows in from the Earth’s polar regions; that air rushes in below the warm air.

The vertical rise of hot air and the rush of cool air to replace it creates horizontal winds at or near the surface of the Earth. Water that evaporates from the land and oceans rises with the ascending warm air. As the water vapor rises, it cools until condensation forms clouds. Clouds result in rain and snow. Wind pushes clouds all over the planet. Weather is what’s happening in the troposphere in the next few minutes, hours, days, and months.