The Earth’s AtmosphereThe Earth’s Atmosphere

• Composition 

• Structure  

• thin layer of gases enveloping Earth • no well-defined upper boundary – just fewer and fewer atoms• density decreases with altitude because number of atoms decrease

What is the Atmosphere?

View of the atmosphere from the space shuttle

Air PressureAir Pressure

• atmosphere – exerts pressure• the pressure is from the mass of the atoms• gravity – compresses air near surface (increase density)• felt by any surface in contact with air •sea level pressure = 15 lb/in2

Composition of AtmosphereComposition of Atmosphere

• atmosphere is a mixture of• gases, solid particles, water droplets• Small changes are always happening

– physical processes (volcanoes), – biological (plants and animals –

transpiration and respiration),

• major gases: N2 and O2 • lesser amounts of noble gases (Ar, Ne, Kr, Xe) • plus Hydrogen (H) and Helium (He) • N2:

• 78% volume • O2:

• 21% volume

Permanent Gases

• Water vapor (H20)• Carbon Dioxide (CO2)• Ozone (O3)

Variable Gases

source of this gas: evaporation from Earth’s surface• water cycle – moves water between oceans, land and atmosphere • 75% Earth’s surface covered by some form of water ground water• extremely important: clouds, absorb energy

Water Vapor

This satellite image shows the relative amounts of water vapor: Dark – low water, white – high water vapor

•sources: respiration, organic decay, volcanoes, natural and man-made caused fires•important Greenhouse gas•More Carbon dioxide means more heating of the Earth

Carbon Dioxide (CO2)

Very emotional issue for Americans - Are we having a bad effect on the atmosphere of the Earth???

OzoneOzone (O(O33))

• consists of 3 O atoms (O2 + O = O3 )

• highest concentration in stratosphere

•shields surface from UV radiation • UV radiation splits O3 molecule

• also contributor to smog effects people and vegetation

Solids and liquids in the atmosphere

• small solid particles and liquid droplets • associated with human and natural processes• larger particulate matter – dust, volcanoes, sea spray and combustion • major component of urban smog

Vertical Structure of the Atmosphere

• no clearly defined upper boundary

• density decreases with elevation

• We divide the atmosphere into layers based on:Changes in temperature

Density Density

• Gravity pulls the atmosphere downward

• atmosphere made up of gases which can be compressed

• lower atmosphere greater density

Temperature Layers from

Earth’s surface

1) Troposphere

2) Stratosphere

3) Mesosphere

4) Thermosphere

Not shown here –The Exosphere!

Let’s learn a little about each layer!

• lowest layer; temperature decreases with altitude

• thinnest layer (8-16 km, avg. 11 km)• where weather occurs• primarily heated by Earth’s surface

Troposphere

Troposphere – when a cloud reaches the top of this layer, they cannot go higher so they flatten out.

Stratosphere

• found above the troposphere

• temperature rises with elevation

• Ozone Layer located here

• upper stratosphere temperature increases with altitude due to absorption of UV (ultraviolet) radiation in the ozone layer

Without the ozone layer protecting us, we could not live on the surface of the Earth!

Mesosphere

• above the stratosphere• temperature decreases with altitude• Meteorites and space dust burns up in this layer

Thermosphere

• above the mesosphere• temperature increases with altitude• contains a special part called the ionosphere

Ionosphere

Quartz Lake State Park, Alaska (Curtis, 1996)

• defined based on electrical characteristics within the thermosphere

• absorbs cosmic rays, gamma rays, X-rays, some UV rays

• contains ions: charged electrical particles

• visible light is emitted when ions are bombarded by cosmic radiation produce aurora borealis, aurora australis