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The Atmosphere

Earth Systems

Planets of the Solar System Section 1

Formation of Solid Earth

The diagram below shows the differentiation of Earth.


Formation of Solid Earth, continued

Present Solid Earth

• Eventually, Earth’s surface cooled enough for solid rock

to form from less dense elements that were pushed

toward the surface during differentiation.

• Earth’s surface continued to change as a result of heat in

Earth’s interior as well as through impacts and through

interactions with the newly forming atmosphere.


Formation of Earth’s Atmosphere

• The atmosphere formed because of differentiation.

• The original atmosphere of Earth consisted primarily of

hydrogen and helium.

Earth’s Early Atmosphere

• Earth’s gravity would have been too weak to hold high

concentrations of hydrogen and helium gases.

• These gases were probably blown away by solar winds.

• Earth’s magnetic field, which protects that atmosphere

from the solar wind, might not have been fully

developed.


Formation of Earth’s Atmosphere, continuedOutgassing

• Volcanic eruptions released large amounts of gases, mainly water vapor, carbon dioxide, nitrogen, methane, sulfur dioxide, and ammonia. This process, known as outgassing, formed a new atmosphere.

• The ozone formed from remaining oxygen molecules after solar radiation caused ammonia and some water vapor to break down.

• The ozone collected in a high atmospheric layer around Earth and shielded Earth’s surface from the harmful ultraviolet radiation of the sun.

The Secondary Atmosphere

� Formed from degassing of volcanoes

� Gases emitted probably similar to the gases emitted by volcanoes today.� H2O (water), 50-60%

� CO2 (carbon dioxide), 24%

� SO2 (sulfur dioxide), 13%

� CO (carbon monoxide),

� S2 (sulfur),

� Cl2 (chlorine),

� N2 (nitrogen),

� H2 (hydrogen),

� NH3 (ammonia) and

� CH4 (methane)

Earth’s Present Atmosphere

Nitrogen (N2)-

78%,

Oxygen (O2)-

21%,

Carbon Dioxide (CO2) 0.03 %,

Where did all the oxygen come from?

Volcanic

outgassing

Modern

Atmosphere

H2O – 50-60% N2 – 78%

CO2 – 24% O2– 21%

SO2 – 13% CO2– 0.03%

1. Where did all the O2 come from?

2. Where did all the CO2 go?


Formation of Earth’s Atmosphere, continuedEarth’s Present Atmosphere

• Organisms that could survive in Earth’s early atmosphere developed.

• Some of these organisms, such as cyanobacteria and early green plants, used carbon dioxide during photosynthesis.

• These organisms produced oxygen as a byproduct of photosynthesis and helped slowly increase the amount of oxygen in the atmosphere.


Reading check, continued

How did green plants contribute to Earth’s present-day

atmosphere?

Green plants release free oxygen as part of

photosynthesis, which caused the concentration of oxygen

gas in the atmosphere to gradually increase.


Formation of Earth’s Oceans

• The first ocean was probably made of fresh water.

• Over millions of years, rainwater fell to Earth and

dissolved some of the rocks on land, carrying those

dissolved solids into the oceans.

• As the water cycled back into the atmosphere through

evaporation, some of these chemicals combined to form

salts. Through this process, the oceans have become

increasingly salty.


Formation of Earth’s Oceans, continued

The Ocean’s Effects on the Atmosphere

• The oceans affect global temperature by dissolving

carbon dioxide from the atmosphere.

• Scientists think that early oceans also affected Earth’s

early climate by dissolving carbon dioxide.

• Carbon dioxide in the atmosphere keeps energy from

escaping into space and thus helps to heat the

atmosphere.

Origin of the atmosphere

� What happened to Earth’s original atmosphere?

� Earth’s original atmosphere was composed mainly of

Hydrogen and Helium. These are very light elements

and were driven off by the solar wind early in Earth’s

history.

� How did Earth’s secondary atmosphere form?

� Earth’s secondary atmosphere formed from

volcanic outgassing. Volcanic eruptions emit H2O,

CO2, N2, CO, SO2. These heavier gases are held in place

by gravity.

Formation of the oceans

� The earth is cool enough that H2O condenses to form the oceans.� Estimates of the amount of H2O

outgassed is not enough to fill the oceans

� It seems likely that a large volume of water was added by the impact of icy meteors on the atmosphere.

� CO2 dissolves into the oceans.

Life evolves in the Oceans

� Ingredients necessary for life� NH3 – ammonia

� CH4 – Methane

� H2O – Water

� These can produce amino acids, the building blocks of life

� Life may have originated

� under the primitive

atmosphere

� at hydrothermal vents deep

in the oceans

� deep in the earth’s crust

Life changes the atmosphere

� With the evolution of life the first cellular organisms (cyanobacteria) began to use the gasses in the early atmosphere (NH3 –ammonia, CH4 – methane, H2O – water) for energy.

Photosynthetic organisms evolve.

These organisms use CO2 and produce oxygen (O2) as a waste product.

� Where did the O2 come from?

� Produced by photosynthetic life.

� Where did the CO2 go?

� Dissolves in water in the oceans

� Used by life during photosynthesis and buried

when plants and micro-organisms die.

� The source of coal and oil

� Held as CaCO3 in limestone (Rocks)

Early history of life and the

atmosphere

� The Earth is about 4.6 billion years old.

� Life first appears in the oceans at least 3.5 billion years ago.

� 0.9 billion years ago there is enough oxygen in the atmosphere to produce the ozone layer and life can finally move onto land.� The ozone layer protects the earth from harmful ultra

violet radiation from the sun.

The other planets

� Venus � Closer to the sun

� Very hot at the surface so water vapor in the atmosphere does not condense.� Runaway greenhouse effect

(482oC, 900oF).

� No oceans or rainfall so CO2

does not dissolve.

� Has a very dense atmosphere.

The other planets

� Mars

� Further from the sun

� Smaller than Earth

� So small that most of the

atmosphere escaped into

space.

� No oceans or rainfall so CO2

stays in atmosphere.

� 98% of atmosphere is CO2.

• Jupiter

– Huge (318x earth’s mass)

– Kept all its original

atmosphere

– 80% Hydrogen

– 20% Helium

Key Ideas

� Describe the composition of Earth’s

atmosphere.

� Identify the layers of the atmosphere.

� atmosphere a mixture of gases that surrounds a

planet, such as Earth

� The most abundant elements in air are the gases

nitrogen, oxygen, and argon.

� The two most abundant compounds in air are

the gases carbon dioxide, CO2, and water vapor,

H2O.

� In addition to containing gaseous elements and

compounds, the atmosphere commonly carries

various kinds of tiny solid particles, such as dust

and pollen.

Composition of the Atmosphere

Modern atmosphere

Nitrogen (N2)-

78%,

Oxygen (O2)-

21%,

Carbon Dioxide (CO2) 0.03 %,

Atmospheric Composition % by Volume

Major ConstituentsNitrogen (N2) 78.08%Oxygen (O2) 20.94%

Active Minor ConstituentsWater vapor (H2O) variable (0.01% at the poles,

5% at the equatorCarbon Dioxide (CO2) 0.037%Methane (CH4) 0.00015%Nitrous oxide (NO2) 0.00005%Ozone (O3) 0.000007%CFC’s 0.00000014%

Inactive Minor ConstituentsArgon 0.83%Neon 0.0018%Helium 0.00052%Krypton 0.0001 %

Xenon 0.000009%

Matter Cycles play an important role

in the Atmosphere

� Physical and biological processes (matter

cycles) maintain Earth’s atmosphere in a

state of chemical disequilibrium.

� Carbon Cycle – photosynthesis and

respiration

� Nitrogen Cycle

� Water Cycle

� Nitrogen makes up about 78% of Earth’s atmosphere and is maintained through the nitrogen cycle.

� Nitrogen is removed from the air mainly by the action of nitrogen-fixing bacteria.

� The bacteria chemically change nitrogen from the air into nitrogen compounds that are vital to the growth of all plants.

� Decay releases nitrogen back into the atmosphere.

Nitrogen in the Atmosphere

Oxygen in the Atmosphere

� Oxygen makes up about 21% of Earth’s atmosphere.

� Animals, bacteria, and plants remove oxygen from the air as part of their life processes.

� Land and ocean plants produce large quantities of oxygen in a process called photosynthesis.

� The amount of oxygen produced by plants each year is about equal to the amount consumed by all animal life processes.

Water Vapor in the Atmosphere

� As water evaporates from oceans, lakes, streams, and soil, it

enters air as the invisible gas water vapor.

� Plants and animals give off water vapor during transpiration or

respiration. But as water vapor enters the atmosphere, it is

removed by the processes of condensation and precipitation.

� The percentage of water vapor in the atmosphere varies

depending on factors such as time of day, location, and season.

Ozone in the Atmosphere

� ozone a gas molecule that is made up of three

oxygen atoms

� Ozone in the upper atmosphere forms the ozone

layer, which absorbs harmful ultraviolet

radiation from the sun.

� Without the ozone layer, living organisms would

be severely damaged by the sun’s ultraviolet

rays.

� Unfortunately, a number of human activities

damage the ozone layer.

Particulates in the Atmosphere

� The atmosphere contains various tiny solid and liquid particles, called particulates.

� Particulates can be volcanic dust, ash from fires, microscopic organisms, or mineral particles lifted from soil by winds. Pollen from plants and particles from meteors that have vaporized are also particulates.

� Large, heavy particles remain in the atmosphere only briefly, but tiny particles can remain suspended in the atmosphere for months or years.

Layers of the Atmosphere

� Earth’s atmosphere as a distinctive pattern of

temperature changes with increasing altitude.

� The temperature differences mainly result from

how solar energy is absorbed as it moves

through the atmosphere.

� Scientists identify four main layers of the

atmosphere based on these differences.

The Troposphere

� troposphere the lowest layer of the

atmosphere, in which temperature drops at a

constant rate as altitude increases; the part of

the atmosphere where weather conditions exist

� At an average altitude of 12 km, the

temperature stops decreasing. This zone is

called the tropopause and represents the upper

boundary of the troposphere.

The Stratosphere

� stratosphere the layer of the atmosphere that lies between the troposphere and the mesosphere and in which temperature increases as altitude increases; contains the ozone layer

� In the upper stratosphere, the temperature increases as altitude increases because air in the stratosphere is heated from above by absorption of solar radiation by ozone.

� The stratopause, about 50 km above Earth’s surface, marks the upper boundary of the stratosphere.

The Mesosphere

� mesosphere the coldest layer of the

atmosphere, between the stratosphere and the

thermosphere, in which the temperature

decreases as altitude increases

� The mesosphere is located above the

stratopause and extends to an altitude of about

80 km.

� The upper boundary of the mesosphere, called

the mesopause, has an average temperature of

nearly −90°C, which is the coldest temperature in the atmosphere.

The Thermosphere

� thermosphere the uppermost layer of the atmosphere, in which temperature increase as altitude increases; includes the ionosphere

� Temperature increases as altitude increases because nitrogen and oxygen atoms absorb solar radiation.

� The lower region of the thermosphere, at an altitude of 80 to 400 km, is commonly called the ionosphere.

� Interactions between solar radiation and the ionosphere cause the phenomena known as auroras.

The Thermosphere, cont’d

� There are not enough data about temperature

changes in the thermosphere to determine its

upper boundary.

� However, above the ionosphere is the region

where Earth’s atmosphere blends into the

almost complete vacuum of space.

� This zone of indefinite altitude, called the

exosphere, extends for thousands of kilometers

above the ionosphere.

This diagram shows

the different layers

of the atmosphere.

Layers of the Atmosphere,

continued

Reading Check

What is the lower region of the thermosphere

called?

The lower region of the thermosphere is called the

ionosphere.

Sun - our star – the source of most of our energy

1st Law of Thermodynamics

� Energy cannot be created nor destroyed,

but energy can be transformed from one

form to another.

2nd Law of Thermodynamics

� In every energy transformation (from one

form to another) energy tends to degrade

from a concentrated “high quality” or

“useful” form, to a dispersed “low quality”,

“less useful” form.

� When energy is converted between forms

some energy is converted into unusable heat.

� This means that a constant supply of energy is

needed to sustain a system over time.

� Energy in = Energy Out

What are the 3 ways heat can be

transferred?

� Radiation: transfer by

electromagnetic waves.

�

Conduction: transfer by

molecular collisions.

�

Convection: transfer by

circulation of a fluid.

Image from: http://www.uwsp.edu/geo/faculty/ritter/geog101/uwsp_lectures/

Insolation (Incoming Solar Radiation)

� Insolation drives nearly all physical and biological processes on earth.

� Of the solar energy striking the earth’s outer atmosphere

� 30-35% is reflected� Clouds reflect 19-24%� Dust and gas molecules in the atmosphere reflect 6-7%� Earth’s surface reflects 3-4%

� 40-45% is absorbed by the atmosphere (heats atmosphere)

� 20-25% Evaporates water to drive the hydrologic cycle.

� 1% generates wind

� <1% is used by green plants for photosynthesis. (this photosynthesis is the basis for virtually all animal life on earth – except for some very specialized biotic communities around deep sea vents)

Heat Budget

Heat Budget

Energy Balance

Energy Balance: (Energy in = energy out)

� The Earth receives energy from the sun.� In turn biological and physical processes

transform the Insolation into other forms of energy.

� Ultimately the energy flowing through the Earth system is emitted back into space.

� If more energy is received and held than is re-radiated then the balance is upset and the earth will warm.

� In contrast if more energy is re-radiated than is received then earth would cool.

Greenhouse effect vs Global Warming

� Greenhouse effect

� The warming of atmosphere that

occurs when carbon dioxide, water

vapor, and other gases absorb and

re-radiate infra-red radiation

(heat). The natural greenhouse

effect allows the atmosphere to

maintain the temperatures needed

for biological processes.

Global Warming

� A gradual increase in the

average global

temperature that is due to

a higher concentration of

greenhouse gases in the

atmosphere.

GreenHouse Gases

Water Vapor (H2O)

� Natural sources water cycle, evaporation

� Human sources increased evaporation,

spray irrigation

� Present concentration 01% at the poles

5% at equator

� Share of effect 98%

� Residence time ~ 9days

Carbon Dioxide (CO2)

� Natural sources� respiration, decomposition, natural fires

� Human sources� burning of fossil fuels, deforestation

� Present concentration� 383ppm (2007)

� Share of effect� 57% of the share not caused by H2O

� Residence time� 3-7 years (200 years ?)

� Rate of increase� 2% per year

� Carbon sinks� seawater, forests, marine organisms, rocks

Mauna Loa Observatory CO2 Measurements

� CO2 in atmosphere today

~383 ppm (2007)

� Estimated pre-industrial

concentration -= 288

ppm

� Highest past level that

we can measure in ice

cores, ~125,000 years

ago (280-300 ppm!)

Chlorofluorocarbons (CFC’s)

� Natural sources NONE – they are synthetic chemicals

� Human sources coolants in air conditioners, freezers,

refrigerators, solvents, foaming

agents, aerosol propellants.

� Present concentration - 2970 ppt(v) 1990

� Share of effect 25% of the 2% not caused by H2O

� Residence time 65-130 years

� Rate of increase ? <5% per year and decreasing

� Potency 1500–7000 times more potent than CO2

� Sinks eventual stratospheric reactions

Methane (CH4)� Natural sources anaerobic bacteria in

wetlands, termites, natural gas escaping from deposits, biomass burning

� Human sources rice paddies, landfills, cattle, oil and gas extraction

� Present concentration 1.7 ppb (v) 1991

� Share of effect 12% of the 2% not caused by H2O


� Rate of increase 1% per year

� Potency 25 times more potent than CO2

Nitrous Oxide (N2O)� Natural sources Forest Fires, grassland fires,

microbes, animal wastes

� Human sources Fertilizer manufacture and use, livestock wastes, fossil fuel burning, biomass burning, nylon production, nitrate contaminated groundwater.

� Present concentration 308 ppb(v) 1990

� Share of effect 6% of part not caused by H2O


� Rate of increase .25% per year

� Potency 230 times more potent than CO2

Notes: residence time is in the atmosphere. CFC’s and N2O are also responsible for Ozone depletion in the atmosphere.

Source: Environmental Notebook, 2001, Fred Montague

� Notes: residence time is in the atmosphere.

CFC’s and N2O are also responsible for Ozone

depletion in the atmosphere.

� Source: Environmental Notebook, 2001, Fred

Montague

Assessment: Answer each of the following questions in a paragraph of 3-5 complete sentences

1. Describe the composition of the Atmosphere.

2. Describe the formation of Earth’s present atmosphere.

3. Explain the three mechanisms of heat transfer in Earth’s Atmosphere.

4. Describe the flow of energy in the atmosphere.

5. Describe the role of Greenhouse gases in Earth’s Atmosphere.

6. How does human activity change some greenhouse gas levels?

7. Describe the role of Ozone in the stratosphere.

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