18. earth&moon

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Terrestrial Worlds 2

Earth - The most unique of all

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Earth basics

• 3rd planet from Sun (1 AU), 5th largest world• Orbit - 1 Earth year

• Sidereal rotation - 23.9 hours (solar day -24 hrs)

•Surface gravity- 9.8 m/s

2

.• 1 bar of pressure

• 78% N221% O

2 < 1% others 0.003 CO

2.

•Temperatures- ~100

o

F summer (max. 140

o

F, deserts) - ~0 oF winter (min. -130 oF, poles)

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Unique Features

• oceans,

• Plate tectonics

• oxygen atm.

• Life!

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EarthquakesDetected earthquakes form lines

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Earth’s Lithosphere broken into pieces~8 large and 10 small plates

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Crust follows Convection Currents• Rising current (hot)

• Plate dragged aside

• Breaks at weakest point(where it is hottest)

• New lava wells into gap. – DIVERGENT boundary

• Falling current drags plate

after it.• 1 plate hits another and

sinks.

– CONVERGENT boundary

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Why Does This Happen?

• The plates float

on a semi-liquid

layer called theasthenosphere

• The liquid allows

slabs to slideunder each

other.

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Earth -tectonics

• All a consequence of internal convection:

– Extension faults occur at upwelling of mid-ocean

ridges (divergent boundary)

– Compression faults occur at downwelling ofsubduction zones (convergent boundary)

– Strike-slip faults occur as plates jostle around,

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Earth -Volcanism

• All a consequence of internal convection:

– Low viscosity lavas occur at upwelling of mid-ocean

ridges -shield volcanoes

– High viscosity lavas occur at subduction zones as

crust is remelted - tall, explosive, stratovolcanoes

Result: Earth is the ONLY world to havestratovolcanoes, because it’s the only world tohave plate tectonics

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Lava erupted at the mid ocean ridge

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Stratovolcano on continent

side of subduction zone

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Earth - Erosion & Surface processes

• Mass wasting

• Wind -deserts

• Biological (unique)

• Water -main process! River Channels erode at head, deposit at mouth

! Materials move along beaches

! Glaciers grind material down

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Water in

Action

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Earth has about 200 craters at the surface.

Earth -Cratering

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Earth’s Volatiles

(atmosphere and hydrosphere)Earth is unique in that:

• the majority of it’s volatiles are liquid.

• Atmospheric composition is not all CO2

(78% N2, 21% O

2 ,<1% others, 0.003 CO

2 )

• Life affects the atmospheric balance.

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Why does Earth have so little atmosphere,unlike Venus?

Why does Earth’s atmosphere consistmostly of nitrogen and oxygen, not CO2?

Why does Earth have oceans?

Important Questions

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Why Does Earth have a

Nitrogen/Oxygen Atmosphere?

• Most of the CO2 is locked up. Nitrogen is

the main ingredient left.

• Plant life produces oxygen, as plantsincrease oxygen levels increase. Largeexcess over time.

• Some of excess oxygen gets broken andremade into ozone

– (3 O2 molecules become 2 O3)

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Earth Oceans and Temperature

Why does Earth have oceans

while Venus and Mars do not?

• Earth is the right temperature to have liquid

water due to distance from the Sun.• Temperatures are maintained by moderate

greenhouse warming

• CO2 balance maintained by oceans and life – (they act as a sink for all the CO

2 that would

otherwise be in the atm. making extra warming)

• Magnetic field prevents H2O breakup.

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© 2014 Pearson Education, Inc.

Why does Earth have the

youngest surface of all the

terrestrial planets today?

A. It is the largest terrestrial planet so its

interior has not cooled too much.B. It is not so close to the Sun that it has lost

its water and developed a thick lithosphere.

C. It rotates rapidly.

D. all of the above

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Terrestrial Worlds 4

Our Moon

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Moon basics

• Earth’s nearest neighbor , 14th largest world• Orbit -27.3 Earth days

• Sidereal day -27.3 Earth days

• Surface gravity -1.61 m/s2 (16% of Earth)

• No global magnetic field

• Only world visited by humans

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Near Side Far Side

Compare and contrast the 2 sides of the Moon

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Maria make up 16% of the Moon’s surface

and almost all of them are on the Near side

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Main lunar materials

• White highlands

– Anorthosite (a rock full of white feldspar)

• Dark maria

– Basalt (black from iron content)

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Volcanism – Maria Formation

• fluid basalts make flood plains that fill large craters• All occur early in lunar history, 3.8-3.2 billion yrs ago

Large impact

craterweakens

crust

Heat build-up

allows lava towell up to

surface

Cooled lava

is smootherand darker

than

surroundings

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Impact cratering

is dominant

process

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Surface Processes• Mass Wasting

• Radiation damage

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Moon vs. Mercury

What do you think is similar about them? What is different?

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•What processes shaped our Moon? – Early cratering still present

– Maria resulted from early volcanic floods

– no shrinkage scarps

• What processes shaped Mercury?

– Cratering similar to Moon,

– some volcanism, but no large floods

– Shrinkage scarps

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Moon Formation

• Early Theories: Capture, Co-formation(twin),broken off from Earth (fission).

• Chemistry of Moon rocks show Moon is both

like and unlike Earth• Result: Impactor Theory

– Moon formed by a giant asteroid striking a

glancing blow on the Earth

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Impactor Theory

Giant impact stripped matter from Earth’s crust

Stripped matter began to orbit

Then accreted into Moon

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Lunar Atmosphere

–Temperatures 225 oF in day

-243oF at night

MoonMoon

–10-14 bars of pressure (negligible)• Gas comes from impacts that eject surface atoms

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© 2014 Pearson Education Inc

Why are smaller terrestrial

bodies such as Mercury or theMoon "geologically dead"?

A. They don't have volcanoes.

B. They cooled off faster than Earth did.

C. They don't have erosion.D. They were hit by fewer meteorites than Earth.

18. earth&moon

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