Introduction to Solar System 3

7/28/2019 Introduction to Solar System 3

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18-Apr-13

IESO

Introduction to Solar System

Part 3


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The Terrestrial Planets

and Earths Moon


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Similar but Different

Terrestrial planets: Mercury

Venus

Earth

Mars

Earths Moon (or simply, the Moon)

All are rocky/metallic, dense.

Smallest two have little/no atmosphere.


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Earths Interior

Core: Highestdensity; nickel andiron

Mantle: Moderatedensity; silicon,oxygen, etc.

Crust: Lowest

density; granite,basalt, etc.


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Terrestrial Planet Interiors

Applying what we have learned about Earths interior toother planets tells us what their interiors are probably like.


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Mass is Key

The differences between theplanets are largely driven by

mass.

Different processes dependon the mass of the planet.

Mass ratioto Earth

Moon 0.012

Mercury 0.055

Mars 0.11

Venus 0.82

Earth 1.00


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Role of Size

Smaller worlds cool off faster and harden earlier.

The Moon and Mercury are now geologically dead.


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Surface Area-to-Volume Ratio

Heat content depends on volume.

Loss of heat through radiation depends on surface area.

Time to cool depends on surface area divided by volume:

Larger objects have a smaller ratio and cool moreslowly.


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Comparative Planetology

We can learn a lot by comparing the planets.

The same processes operate on each planet:

Tectonism (moving crustal plates)

Volcanism (volcanoes) Impacts (cratering)

Gradation (smoothing by weathering and erosion)

These processes are stronger or weaker on the different

planets.


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Geological Processes

Impact cratering

Impacts by asteroids or comets

Volcanism

Eruption of molten rock onto surface Tectonics

Large scale disruption of a planets surface by internalstresses

Weathering and Erosion Surface changes made by wind, water, or ice


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Impact Cratering

Most cratering happened soonafter the solar system formed.

Craters are about 10 timeswider than the objects that

made them. Small craters greatly

outnumber large ones.


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Impact Craters

Meteor Crater (Arizona) Tycho (Moon)


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Impact Craters

Craters on the Moon are relics of the last phase ofplanetary accretion, which ended about 4 billion years

ago.

All terrestrial planets experienced this.

Venus and Earth have few craters.

Subsequent tectonism and erosion erases the craters.

Some large impacts on the Earth have influenced the

evolution of life.


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Cratered Region on the Moon

NASA/JSC


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On the Moon

Rocks returned in the Apollo missions (1969-1972) giveages.

Rocks from different places show rate of accretion in

the early Solar System.

Accretion rate fell sharply after a billion years.

Older surfaces have more craters because they were

formed when the cratering rate was higher.


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Cratering Rate

NASA/JPL/Caltech


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Formation of the Moon

Moon formed in a large collision betweenEarth + Mars-sized planetesimal (or protoplanet).

The collision scattered material into Earth orbit; thiscollected by accretion to form the Moon.

Composition of Moon is like that of Earths crust.

Dark areas on Moon (maria) are ancient lava flowsfrom the interior due to volcanism associated withheating by major impacting.


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A Model of the Earth

We model the Earths interior by studying earthquakes. Earthquake waves (seismic waves) travel at different

speeds through different materials.

P (primary) waves travel through solids and liquids.

S (secondary) waves go through solids only.

Earths layers are: crust, mantle, liquid outer core, solidinner core


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The Earths Interior

Layers: Crust: continents (low density silicates) and ocean basins

(basalt: higher iron content).

Mantle. (Iron-magnesium rich silicate minerals)

Core (iron, nickel and other dense materials).

Produced by differentiation in the early Earth: dense

materials sink; low-density materials rise.


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How do we know whats inside a planet?

P waves push

matter back and

forth.

S waves shake

matter side toside.


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How do we know whats inside a planet?

P waves go

through Earths

core, but S waves

do not.

We conclude that

Earths core must

have a liquid outerlayer.


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The EarthsInterior


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Models of Other Terrestrial Planets

Interiors are hot, while surfaces are cool. The planets were molten when formed, then

experienced differentiation.

Smaller planets lose heat faster, large ones slower.

Smaller planets have less radioactive material.

These and other effects are included in models.

I t i f th Pl t


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Interiors of the Planets


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Tectonism on Earth

Interior heat flows to the surface, producingvolcanoes and motion of lithospheric plates in a

process referred to asplate tectonics.

Lithospheric plates are moved around by convection

within the mantle.

Convection = rising and falling of hot/cold material.

Motion of interior core material also generates

magnetic fields. Planet rotation may also beimportant.


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Tectonics

Convection of the mantle creates stresses in the crust called tectonicforces.

Compression forces make mountain ranges.

A valley can form where the crust is pulled apart.
http://e/tectonics_convect_of_mantle.htm


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Major Tectonic Plates


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Plate Motion

Motion of plates can be measured with GPS.


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Planetary Magnetic Fields

Moving charged particles create magnetic fields.

A planets interior can create magnetic fields if its core is

electrically conducting, convecting, and rotating.


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Earths Magnetic Field


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Earths MagnetosphereEarths magnetic field protects us from charged

particles from the Sun.The charged particles can create aurorae (Northern

lights).


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Earth: Tectonism and Magnetism

Laboratory: mid-Atlantic ridge. Plates spreading apart, new material rises in the gap.

Solidifying material shows magnetic field at the time.

Direction of the field reverses periodically. Rock ages reveal rates ofplate motion.

Atl ti O B i


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Atlantic Ocean Basin

Mid-Atlantic Ridge


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Mid-Atlantic Ridge


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Volcanism

Volcanism happenswhen molten rock(magma) finds a paththrough lithosphere to

the surface.

Molten rock is calledlava after it reaches thesurface.


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Outgassing

Volcanism alsoreleases gases from

Earths interior intothe atmosphere.


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Weathering and Erosion

Large planets also have atmospheres, producing erosionby wind.

On the Earth, water, wind, and ice strongly erode

features.

This erases old features like craters.

Planets lacking atmospheres, running water, and

moving ice retain craters and other ancient features.


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Erosion

Erosion is a blanket term for weather-drivenprocesses that transport broken down rock material.The transported material is referred to as sediment

Processes that cause erosion include

Glaciers (moving ice)

Rivers (running water)

Wind (air currents)


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Erosion by Water

The ColoradoRiver continues to

carve the Grand

Canyon.


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Erosion by Ice

Glaciers carved theYosemite Valley.


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Erosion by Wind

Wind wears awayrock and builds up

sand dunes.


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Erosional Debris

Erosion can createnew features by

depositing debris.

H d E h h ff


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How does Earths atmosphere affect

the planet?


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Effects of Atmosphere on

Earth1. Erosion

2. Radiation protection

3. Greenhouse effect

4. Makes the sky blue!


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Radiation Protection

All X-ray light is

absorbed very high in the

atmosphere. Ultraviolet light is

absorbed by ozone (O3).


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Earths atmosphere absorbs light at most wavelengths.


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The Greenhouse Effect


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A Greenhouse Gas

Any gas that absorbs infrared

Greenhouse gas: molecules with two different types of elements

(CO2, H2O, CH4)

Not a greenhouse gas: molecules with one or two atoms of the

same element (O2, N2)


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Why the sky is blue

Atmosphere scatters bluelight from the Sun, makingit appear to come fromdifferent directions.

Sunsets are red because lessof the red light from theSun is scattered.

h h l d?


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What have we learned?

Why is Earth geologically active? Earth retains plenty of internal heat because

it is large for a terrestrial planet.

That heat drives geological activity, keeping

the core molten and driving geological

activity.

The circulation of molten metal in the core

generates Earths magnetic field.

Wh h l d?


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What geological processes shape Earths surface?

Impact cratering, volcanism, tectonics, and erosion

How does Earths atmosphere affect the planet?

Erosion

Protection from radiation

Greenhouse effect


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Histories of the Terrestrial Worlds


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Mercury and the Moon: Geologically

Dead

Was there ever geological activity on the

Moon or Mercury?


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Moon

Some volcanic activity 3 billion years ago must have flooded

lunar craters, creating lunar maria. The Moon is now geologically dead.


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Cratering of Mercury

Mercury has a mixtureof heavily cratered andsmooth regions like theMoon.

The smooth regions are

likely ancient lavaflows.


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Tectonics on Mercury

Long cliffs indicate thatMercury shrank early inits history.

Wh t h l d?


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Was there ever geological activity on the Moonor Mercury?

Early cratering on the Moon and Mercury is still

present, indicating that activity ceased long ago.

Lunar maria resulted from early volcanism. Tectonic features on Mercury indicate early

shrinkage.

h


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Mars versus Earth

50% Earths radius, 10% Earths mass 1.5 AU from the Sun

Axis tilt about the same as Earth

Similar rotation period

Thin CO2 atmosphere: little greenhouse

Main difference: Mars is SMALLER


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Storms on Mars

Seasonal winds on Mars can drive huge dust storms.

Sand Dunes on Mars


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Sand Dunes on Mars

NASA/JPL

Malin Space Science

Systems

Evidence that Water Once Existed on the


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Evidence that Water Once Existed on the

Surface of Mars

While there is no running water on Mars today, there isplenty of evidence that it once existed on the surface.

Most of this evidence is in the form of dry channels on

the surface of Mars that were formed by running water.

Water existed on the surface of Mars several billionyears ago, when the atmosphere of the planet was

thicker and the temperature was warmer.


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The surface of Mars appears to have ancient riverbeds.

W F d G lli


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Water Formed Gullies

This dramatic view of gulliesemergent from layered outcrops

occurs on the wall of a crater within

the much larger impact basin,

Newton. Newton Crater and its

surrounding terrain exhibit many

examples of gullies on the walls of

craters and troughs. The gulliesexhibit meandering channels with

fan-shaped aprons of debris

located downslope. The gullies are

considered to have been formed by

erosion--both from a fluid (such as

water) running downslope, and by

slumping and landsliding processes

driven by the force of gravity. This

picture was obtained by the Mars

Global Surveyor (MGS) Mars Orbiter

Camera (MOC) in March 2001; it is

illuminated from the upper left and

covers an area 3 km (1.9 mi) across.(from: http://mars.jpl.nasa.gov/gallery/waterfeatures/20020418e.html)

uno anne sp o os rom arsGl b l S (MGS) M O bi


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pGlobal Surveyor (MGS) Mars Orbiter

Camera (MOC)

(from: http://mars.jpl.nasa.gov/gallery/waterfeatures/PIA01038.html)

anne ze anyonC t b R i
http://photojournal.jpl.nasa.gov/catalog/PIA01038


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Cut by Running

Water

This picture of a canyon on the Martian

surface was obtained a few minutes after

10 PM PST, January 8, 1998 by the Mars

Orbiter Camera (MOC), during the 87th

orbit around Mars of the Mars Global

Surveyor spacecraft. It shows the

canyon of Nanedi Vallis, one of the

Martian valley systems cutting through

cratered plains in the Xanthe Terra

region of Mars. The picture covers an

area 9.8 km by 18.5 km (6.1 mi by 11.5

mi), and features as small as 12 m (39 ft)

can be seen.

(http://mars.jpl.nasa.gov/gallery/waterfeatures/PIA01170.html)


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Scientifically, perhaps themost important result from use

of the Mars Orbiter Camera on

NASA's Mars Global Surveyor

during that spacecraft's

extended mission has been

the discovery anddocumentation of a fossil

delta. The feature is located in

a crater northeast of Holden

Crater, near 24.0 degrees

south latitude, 33.7 degrees

west longitude. The imagecovers an area of about 3 by 3

kilometers (1.9 x 1.9 miles).

FOSSIL DELTA

NASA CONCEPTION OF MARS WITH


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WATER FOUR BILLIONS YEAR AGO

(http://www.spacetoday.org/SolSys/Mars/MarsThePlanet/MarsWater.html)

N th d S th P l I C
http://www.spacetoday.org/SolSys/Mars/MarsThePlanet/MarsWater.html


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North and South Polar Ice Caps

(from: http://www.spacetoday.org/images/Mars/MarsSurfaceFeaturesLabeled.jpg)


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Volcanoesas recent as 180 million years ago


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Past tectonic activity

Why did Mars change?


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Why did Mars change?

Climate Change on Mars


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Climate Change on Mars

Magnetic field may have preserved early Martianatmosphere.

Solar wind may have stripped atmosphere after fielddecreased because of interior cooling.



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What geological features tell us that water once flowed

on Mars? Dry riverbeds, eroded craters, and rock-strewn floodplains all

show that water once flowed on Mars.

Mars today has ice, underground water ice, and perhapspockets of underground liquid water.

Why did Mars change? Marss atmosphere must have once been much thicker for its

greenhouse effect to allow liquid water on the surface.

Somehow Mars lost most of its atmosphere, perhaps becauseof a declining magnetic field.

l i ll i


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Is Venus geologically active?


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Cratering on Venus

Impact craters, but fewer thanMoon, Mercury, Mars


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Volcanoes on Venus

Many volcanoes


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Tectonics on Venus

Fractured and contortedsurface indicatestectonic stresses


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Erosion on Venus

Photos of rockstaken by landershow little erosion


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Does Venus have plate tectonics?

Most of Earths major geological featurescan be attributed to plate tectonics, whichgradually remakes Earths surface.

Venus does not appear to have platetectonics, but its entire surface seems tohave been repaved 750 million years

ago.

Why is Venus so hot?


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The greenhouse effect on Venus keeps its surfacetemperature at 470C.

But why is the greenhouse effect on Venus so much

stronger than on Earth?

Greenhouse Effect on Venus


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Greenhouse Effect on Venus

Thick carbon dioxideatmosphere producesan extremely stronggreenhouse effect.

Earth escapes thisfate because most ofits carbon and waterare in rocks andoceans.



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Is Venus geologically active?

Its surface shows evidence of major volcanism and tectonics

during the last billion years.

There is no evidence for erosion or plate tectonics.


The runaway greenhouse effect made Venus too hot for liquidoceans.

All carbon dioxide remains in the atmosphere, leading to a

huge greenhouse effect.

What unique features of Earth are


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important for life?

1. Surface liquid water

2. Atmospheric oxygen3. Plate tectonics

4. Climate stability

Water is Necessary for Life


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Water is Necessary for Life

Water in abundance exists only on the Earth. None on Mercury (too hot) or the Moon (too small).

None on Venus (too hot).

Mars: water ice below surface.

Mars may once have had surface water:

Chemical composition of certain minerals.

Erosion features.



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important for life?


2. Atmospheric oxygen

3. Plate tectonics


Earths distance from the Sun and

moderate greenhouse effect make

liquid water possible.



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important for life?



3. Plate tectonics

4. Climate stabilityPHOTOSYNTHESIS (by plants and

certain bacterial life) is required to

make high concentrations of O2,

which produces the protective layer

of O3.



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important for life?



3. Plate tectonics


Plate tectonics is an

important step in the

carbon dioxide cycle.

Seafloor Recycling


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Seafloor Recycling

Seafloor is recycled through a process known assubduction.

Carbon Dioxide Cycle


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1. Atmospheric CO2dissolves in rainwater.

2. Rain erodes minerals

that flow into theocean.

3. Minerals combine withcarbon to make rocks

on ocean floor.



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4. Subduction carriescarbonate rocks downinto the mantle.

5. Rock melts in mantleand outgases CO2back into atmospherethrough volcanoes.



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important for life?



3. Plate tectonics

4. Climate stabilityThe CO2 cycle acts like a

thermostat for Earths

temperature.

Long-Term Climate Change


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Long Term Climate Change

Changes in Earths axis tilt might lead to ice ages.

Widespread ice tends to lower global temperatures byincreasing Earths reflectivity.

CO2 from outgassing will build up if oceans are frozen,ultimately raising global temperatures again.

How is human activity changing our


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How is human activity changing our

planet?

Gl b l W i


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Global Warming

Earths averagetemperature hasincreased by 0.5C inthe past 50 years.

The concentration ofCO2 is rising rapidly.

An unchecked rise ingreenhouse gases willeventually lead to global

warming.

CO2 Concentration


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CO2 Concentration

Most of the CO2 increase has happened in the last 50 years!

Modeling of Climate Change


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Modeling of Climate Change

Models of globalwarming that includehuman production ofgreenhouse gases are a

better match to theglobal temperaturerise.

What makes a planet habitable?


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p

Located at an optimal distance from the Sun for

liquid water to exist

What makes a planet habitable?


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p

Large enough for geological activity to release and

retain water and atmosphere

Planetary Destiny


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Earth is habitable

because it is large

enough to remain

geologically active,

and it is at the right

distance from theSun so oceans could

form.

Documents

Introduction to Solar System 3