Earth's atmosphere

Earth's Atmosphere is the layer of gases, commonly known as air, that surrounds the planet Earth and is retained by Earth's gravity. The atmosphere of Earth protects life on Earth by creating pressure allowing for liquid water to exist on the Earth's surface, absorbing ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night (the diurnal temperature variation).

Composition

The Earth's atmosphere is composed of 78% nitrogen (N2), 21% oxygen (O2), 0.93% argon (Ar), 0.04% carbon dioxide (CO2), and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere.

Layers

The atmosphere of Earth can be divided into five main layers. These layers are the troposphere, stratosphere, mesosphere, thermosphere, and the exosphere. Each layer has a different lapse rate, defining the rate at which temperature decreases with an increase in altitude.

Troposphere

The troposphere is the lowest layer of Earth's atmosphere. It extends from Earth's surface to an average height of about 12 km, although this altitude varies from about 9 km at the poles to 17 km at the equator, with some variation due to weather. The troposphere is bounded above by the tropopause, a boundary marked in most places by a temperature inversion (i.e., a layer of relatively warm air above a cooler one), and in others by a zone which is isothermal with height.

Stratosphere

Above the troposphere, the stratosphere is the second-lowest layer of Earth's atmosphere. It extends from the tropopause to about 50 km. The ozone layer, which absorbs and scatters the solar ultraviolet radiation, is in the stratosphere.

Mesosphere

The mesosphere is above the stratosphere and extends from about 50 to 85 km above the Earth's surface. It is where most of the meteors burn up upon entering the Earth's atmosphere.

Thermosphere

The thermosphere extends from the mesopause at an altitude of about 85 km up to the thermopause at an altitude of 500 to 1,000 km. The auroras occur in the thermosphere.

Exosphere

The outermost layer of Earth's atmosphere is the exosphere. This layer extends from the thermopause to the exobase, which is located at about 10,000 km above the Earth's surface. The exosphere merges into the solar wind.

Importance

The Earth's atmosphere is crucial for life as it provides essential elements such as oxygen for humans and animals and carbon dioxide for plants. It also protects living organisms from genetic damage by solar ultraviolet radiation, solar wind, and cosmic rays. The atmosphere moderates Earth's temperature, making it habitable, and transports water vapor, providing water to land through precipitation.

Climate and Weather

The Earth's atmosphere is a key factor in determining the planet's climate and weather patterns. It circulates heat and moisture around the globe, contributing to the weather systems and climatic zones.

Human Impact

Human activities, such as the burning of fossil fuels and deforestation, have significantly altered the composition of the atmosphere, contributing to climate change. These changes threaten the stability of Earth's climate system and have far-reaching effects on human and natural systems.

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