The Atmosphere

Chapter 3, Section 2

Learning ObjectivesDescribe the composition and layers of the

Earth’s atmosphere.Explain three mechanisms of heat transfer in

Earth’s atmosphere.Explain the greenhouse effect.

The AtmosphereAtmosphere – the mixture of gases that

surrounds the EarthContains mostly nitrogen, oxygen, carbon

dioxideThese gases are constantly added and

removedAnimals and humans breath in and outPlants produce foodVolcanoes eruptCars

Composition of the

AtmosphereNitrogen = 78%•Volcano eruptions•Dead plants and animals decay

Oxygen = 21%•Plants

Other Gases = 1%•Argon•Carbon Dioxide•Methane•Water Vapor

Composition of the AtmosphereAtmosphere also contains atmospheric dust

Mainly soilSaltAsh from firesVolcanic ashParticulate matter from combustionSkinHairBits of clothingPollenBacteria and virusesaerosols

Air PressureEarth’s atmosphere is pulled toward Earth’s

surface by gravityThis makes the atmosphere denser near

Earth’s surfaceAlmost the entire mass of Earth’s

atmospheric gases is located with 30 km of the surface.

The air is less dense at higher altitudes. This makes breathing more difficult.

Layers of the AtmosphereThe atmosphere is divided into four layers

based on temperature changes that occur at different distances above the Earth’s surface.TroposphereStratosphereMesosphereThermosphere

The TroposphereClosest to Earth’s surface18 km above Earth’s surfaceAlmost all weather occurs hereDensest atmospheric layerTemperature decreases as altitude increases

The StratosphereFrom 18 km to about 50 kmTemperature rises as altitude increases in

stratosphereOzone in the stratosphere absorbs the sun’s

ultraviolet (UV) energy and warms the airOzone, O3, is made up of three oxygen atomsAlmost all ozone in the atmosphere is located

in the ozone layer of the stratosphereOzone reduces the amount of UV radiation

that reaches Earth.

The MesosphereFrom 50 km to 80 km above Earth’s surfaceThe coldest layer of the atmosphereTemperatures as low as -93°C.

The ThermosphereThe layer farthest from the Earth’s surfaceNitrogen and oxygen absorb solar radiation

The absorption causes atoms to be electrically charged.

These ions radiate energy as light.Temperatures above 2,000°CIf we could travel here, it would not feel hot to

usAir particles that strike one another transfer heatThe air in the thermosphere is so thin that air

particles rarely collide so they rarely transfer heat.

Three Types of Heat TransferRadiation – Transfer of energy across space

Conduction – Flow of heat from a warmer object to a colder object when placed in direct contact

Convection – The transfer of heat by air currents

Conduction, Convection, Radiation

Heating of the AtmosphereSolar energy reaches Earth as

electromagnetic radiation.Electromagnetic radiation includes visible

light, infrared radiation, and ultraviolet light.Almost half of the solar energy that enters

the atmosphere passes through and reaches Earth’s surface

The rest is absorbed in the atmosphere by clouds, gases and dust or it is reflected by the Earth’s surface.

Movement of Energy in the AtmosphereWeather is caused by air that is constantly

moving upward, downward or sidewaysCurrents of less dense air, warmed by the Earth’s

surface, rise into the atmosphere.Currents of denser, cold air sink toward the

ground.As currents of air rise into the atmosphere they

cool offEventually, the air current becomes more dense

than the air around it and sinks.Convection current – Continual process of warm

air rising and cool air sinking. A circular motion.

The Greenhouse EffectA greenhouse is a

building where plants are grown.

Solar radiation enters the building and heats up the inside faster than heat can escape.

Greenhouse GasesGreenhouse Gases – The gases in our

atmosphere that trap and radiate heatNone of the greenhouse gases have a high

concentration in the Earth’s atmosphereThe most abundant greenhouse gases are

Water vapor (varies because of natural processes)

Carbon dioxide (varies because of industry)Methane (varies because of industry)Nitrous oxide

The Greenhouse EffectThe gases in Earth’s atmosphere act like the glass in a

greenhouse.Sunlight penetrates the Earth’s atmosphere and heats

the surface of the Earth.The Earth’s surface radiates heat back to the

atmosphere where only some of the heat escapes into space.

The rest of the heat is absorbed by the greenhouse gases, which warms the air.

Heat is then radiated back toward the surface of the Earth.

Without the greenhouse effect Earth would be too cold to live.