Earth’s Atmosphere The Earth is surrounded by a blanket of air called the atmosphere. It extends over 372 miles (560 kilometers) from the surface of Earth It protects us from high-energy radiation and the frigid vacuum of space The atmosphere absorbs energy from the Sun, recycles water and other chemicals and works with the electrical and magnetic fields of Earth to provide a moderate climate

Composition of the Atmosphere The atmosphere is made up of a mixture of atoms and molecules of different kinds of gases Each type of gas has important uses and roles for our planet Nitrogen, oxygen and argon are the primary components 1% other 21% oxygen 78% nitrogen There are other very influential components including water, “greenhouse” gases or ozone and carbon dioxide

Layers of the Atmosphere Four distinct layers have been identified using temperature changes, chemical composition, movement and density: Troposphere Stratosphere Mesosphere Thermosphere

Layers of the Atmosphere Thermosphere Exosphere Ionosphere Mesosphere Stratosphere Troposphere

The Troposphere The troposphere starts at the Earth’s surface and extends more than 9 miles above the equator to less than 5 miles above the North and South Poles Tropo means “turning” or “changing” Most dense part of the atmosphere As you climb higher, the temperature drops from about 17 to -52° C Almost all weather occurs at levels below 10 miles

The Stratosphere The stratosphere extends from the top of the troposphere to about 31 miles above Earth’s surface Strato is similar to stratum which means “layer” or “spreading out” The lower stratosphere is –60° C The upper stratosphere is actually warmer than the lower stratosphere because of a thin layer of ozone, which absorbs energy form the sun which is converted to heat

The Mesosphere Above the stratosphere, a drop in temperature marks the beginning of the next layer, the mesosphere Meso means “middle” It begins about 31 miles above Earth’ surface and ends at approximately 53 miles high. The outer mesosphere is the coldest part of the atmosphere, with temperatures near - 90° C

The Thermosphere The outermost layer is called the thermosphere, which extends from about 53 miles above Earth’s surface outward into space. It is actually divided into two separate layers: Ionosphere and Exosphere Thermo means “heat” The air is very thin in the thermosphere and extremely hot, up to 1800° C

The Thermosphere The lower layer of the thermosphere is called the ionosphere and begins about 53 miles above Earth’s surface and ends around 372 miles Energy from the sun causes gas molecules to become electrically charged particles called ions Radio waves bounce off these ions and back to the Earth The brilliant light display of the aurora borealis (Northern Lights) also occurs in the ionosphere

The Thermosphere: Exosphere The upper layer of the thermosphere is called the exosphere and extends from 372 miles outward for thousands of miles Satellites orbit in the exosphere

Energy in the Atmosphere Solar energy is mostly visible light and infrared radiation, and a small amount of ultraviolet radiation Most of the energy that keeps Earth warm comes from the Sun. Some of this energy is reflected or absorbed in the atmosphere. The rest reaches Earth’s surface, where it is reflected or absorbed Gases and particles in the atmosphere absorb solar energy Clouds, dust and gases in the atmosphere reflect and scatter light Some energy that reaches the surface is reflected back into the atmosphere Earth’s surface absorbs solar energy. This energy heats the land and water Some of the absorbed energy is then radiated back into the atmosphere

Heat Movement in the Troposphere Radiation, conduction and convection work together to heat the troposphere. When Earth’s surface absorbs solar energy during the day, the surface becomes warmer than the air. The air near the Earth’s surface is warmed by radiation and conduction of heat from the surface to the air.