Earth and the of the Terrestrial (Bennett et al. Ch. 9)

Major Ideas In This Chapter

● Terrestrial planets looked (largely) the same when they were formed. Differences due to geological processes.

● Geological activity is driven by internal heat

● Planetary size plays a large role in retaining heat

● Distance from the , rotation affects

● Crater density can indicate surface age

● has a unique geology

Terrestrial Planets

● Compared to Jovian planets: – Smaller size/mass – Large “core” to atmosphere ratio – Higher density – Closer to Sun and closer together – Warmer – Few or no – No rings

(NASA) Planetary Surfaces and Interiors

● Terrestrial planets + were similar when young – Subjected to heavy bombardment – Differences due to processes that occurred after formation ● Understanding the surface features:

● Processes in the interior drive activity at the surface

Your book uses “terrestrial worlds” to refer to the terrestrial planets + the Moon.

(from Bennett et al.)

(from Bennett et al.) How Do We Learn About Planetary Interiors?

● Average density determinations ● Local variations as measured with artificial satellites ● Magnetic fields: molten core/ ● flow: internal composition ● Earthquakes: internal structure

Earthquakes: Seismic Waves

● Earthquakes generate vibrations – Typical wavelength ~ several km – Reconstruct interior ● Two types of waves: – P-waves: compressional waves – S-waves: shear waves ● S-waves cannot pass through liquid (from Bennett et al.) – Earth's interior has liquid layer ● Monitoring also done on the Moon

(from Morrison and Owen) Interior Structure of Terrestrial Planets ● Density stratification – Core

● , ● Earth has liquid outer core – core ● Rocky layer (minerals with silicon, oxygen, ...) – Crust mantle ● granite, basalt

Interior Strength

crust ● Most of earth's interior: solid – Rock varies in strength – Can deform and flow ● Lithosphere

● Below lithosphere: higher T → core rock flows easier

● Lithosphere “floats” on the soft rock below mantle

● Thickness important

lithosphere How does lithosphere thickness affect volcanic eruptions/ formation? Why Layering?

● Differentiation – Gravitational separation of materials with different densities ● Interiors were hot initially → rock/metal molten

Why are planets round?

Phobos and Deimos (the moons of ) (NASA) Planetary Interiors

(from Bennett et al.)

● We expect smaller planets to have smaller cores – ? – Moon? ● Small planets = thicker What Drives Geological Activity?

● Heat – In general: bigger = more heat ● How do we heat? – Accretion – Differentiation – Radioactivity

Which of these processes is still taking place in terrestrial planets?

What about sunlight?

These processes result in the core/mantle/crust structure What Drives Geological Activity?

● How do we cool? – Convection – Conduction – Radiation ● Example: Earth: – Convection in interior (flowing solid rock) – Above lithosphere, too rigid to flow—conduction takes over – At surface: radiation

What Drives Geological Activity?

(from Bennett et al.) Planetary Size

● Larger planets remain hotter longer

● Mercury/Moon – Cooled quickly (~ 1 billion years) – Lithosphere thickens, mantle convection stops – Geologically dead ● – Similar in size to Earth, so probably still active ● Mars – Cooled more—unclear if the deep interior is still convecting

Cooling Terrestrial Planets Interiors

Total store of heat is proportion to the 's volume,

Energy is only lost through the surface—rate of energy loss is proportion to the surface area of the planet,

Cooling time is related to the total amount of heat/energy stored / rate of energy loss (volume to surface ratio)

Planetary Cores and Magnetic Fields

● Magnetic fields are generated in some planets

● What is needed to generate a ?

B-field why?

Mercury yes large metal core (despite slow rotation) Venus no rotation too slow Earth yes molten rock Moon no cooled off Mars no no metallic core or cooled Planetary Cores and Magnetic Fields

(from Bennett et al.)

Shaping Surfaces

● Impact Cratering – More small than large craters – All terrestrial planets had impacts – Impact at 40,000 to 250,000 km/h

● Craters are circular ● D ~ 10x impactor size ● Depth ~ 10-20% diameter ● Sometimes: central peak

Tycho crater on the Moon ( NASA) (from Bennett et al.) Impact Craters

Shaping Surfaces

● – The eruption of molten lava onto surface – Magma rises: lower density / trapped gases / squeezed – Result depends on how easily lava flows

(from Bennett et al.) Shaping Surfaces

● Volcanism (cont.) – Volcanic and shield volcanoes made of basalt (high density, but runny)

● all terrestrial planets and some Jovian moons show volcanic plains or shield volcanoes—basalt common – Stratovolcanoes made of lower-density rock—rare outside of Earth. – Volcanoes outgas atmospheres

● Atmospheres of Venus, Earth, and Mars, and Earth's oceans came from outgassing

Solar System

The Culann Patera on 's moon Io ( Project, JPL, NASA)

Olympus Mons on Mars—the largest volcano in the (Mars Global Surveyor Project, MSSS, JPL, NASA) Shaping Surfaces

● Tectonics – Surface changes due to forces acting on lithosphere – Most tectonic features arise from mantle convection

● Compression features ● Cracks and valleys – Fractured lithosphere →

(from Bennett et al.) Shaping Surfaces

● Erosion – Breakdown/transport of rock

● Glaciers ● Rivers ● Wind ● ... – Erosion can build (sand dunes, river deltas, ...) – Erosion makes sedimentary rock

Effect of Planetary Properties

● Volcanism/Tectonics – Requires internal heat → planetary size matters

● Which planets had volcanism/tectonics initially? – Moon/Mercury already cooled – Earth large → still active – Venus similar to Earth → still active? – Mars should be cooler inside, much less activity than past

Effect of Planetary Properties

● Erosion – Requires weather (wind, rain, ...) – How does planetary size affect an atmosphere? – Distance from Sun (how does this affect things?) – Rotation (why?) – Moon/Mercury: no atmosphere → no erosion – Mars: thin atmosphere → little erosion – Venus/Earth: thick atmospheres

● Earth cooler: oceans form. Still lots of erosion. ● Venus slow rotator: little erosion

(from Bennett et al.)

(from Bennett et al.) Impact Craters and Age

maria highlands ● All planets impacted during heavy bombardment – Old surface = high crater density

● Lunar highlands – Age ~ 4.4 billion years

● Maria – Age ~ 3.0 – 3.9 billion years

● Heavy bombardment ended ~4 billion years ago

● Impact history on moon applies to other planets Apollo 16 image of the moon (mostly far ● Crater counts → geological age side) (NASA) and Mercury

MESSENGER image of Mercury Apollo 16 image of the moon http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?page=1 &gallery_id=2&image_id=143 (mostly far side) (NASA) Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington ● Many craters ● Cooled long ago—little recent tectonic/volcanic activity ● No atmospheres—no erosion

● Ancient volcanic features—active when young Terrestrial Planets

(from Bennett et al.)

Mass Radius Density Mercury 0.055 M 0.382 R 5.43 g cm-3   Venus 0.815 M 0.949 R 5.25 g cm-3   Earth 1.0 M 1.0 R 5.52 g cm-3   Moon 0.012 M 0.272 R 3.34 g cm-3   Mars 0.107 M 0.533 R 3.93 g cm-3   Overview of the Moon

● Smallest of the terrestrial worlds ● Heavily cratered highlands ● Smooth maria: lava plains ● Some tectonic features ● No erosion ● Geologically dead today. Crater counts, calibrated on the Moon, allow us to determine geological age

Apollo 15 image of Mare Imbrium (NASA; http://sse.jpl.nasa.gov/multimedia/display.cfm?IM_ID=863)

Geology of Moon

● Highlands: bright, heavily cratered

● Maria: smooth, dark regions

● Craters should be roughly uniform—what happened in Maria?

● Lava runny—lack of water/trapped gases

(NASA/Apollo 17) (Luc Viatour/Wikipedia) Geology of Moon

(from Bennett et al.)

Geology of Moon

● Tectonic features found in maria – Contraction during cooling ()

Apollo 15 image of Mare Imbrium (NASA; http://sse.jpl.nasa.gov/multimedia/display.cfm?IM_ID=863)

High iron content in the Maria

S

o

u

r

c

e

:

C

l

e

m

e

n

t

i

n

e

P

r

o

j

e

c

t

d

a

t

a

b

a

s

e

Maria are composed of basalt. Lunar basalt has a higher iron content than on earth.

(NASA/LPI) Lunar far side is at higher elevation than Earth-facing side. Why? Today's Moon

● No geological activity ● Major impacts infrequent ● No wind/weather ● Micrometeorite impacts break up surface rock into powder

Apollo 11 footprint. (NASA; Apollo 11, AS11-40-5878)

Overview of Mercury

● Lots of craters (lower density than Moon)

● Volcanic resurfacing – Small lava plains

● Cliffs and shrinking of planet

● Geologically dead

MESSENGER image of Mercury http://messenger.jhuapl.edu/gallery/sciencePhotos/image .php?page=1&gallery_id=2&image_id=143 Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Scarp radial to Caloris Basin (NASA/ 10) Mercury

● Innermost planet

● No activity

● No atmosphere

● Hot on day side, cold on night side (100 K)

● Rotates 3 times for every two

● Unusually high density Distance from Sun: 0.39 AU radius: 0.38 R ⊕ mass 0.055 M Mercury as imaged by the MESSENGER ⊕ -3 average density: 5.43 g cm http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=7543 composition: rocks, metal Credit: NASA/Johns Hopkins University Applied Physics moons: 0 Laboratory/Carnegie Institution of Washington Mercury from Earth

http://www.nasa.gov/mission_pages/solar-b/solar_015.html

Geology of Mercury

● Lots of impact craters = old surface

● Lower crater density than some lunar regions – Resurfacing by lava flows? – Small lava plains – Volcanically active when young

MESSENGER image of Mercury http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?page=1 &gallery_id=2&image_id=143 Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Mare Orientale (Moon) as imaged by NASA's Lunar Orbiter 4 (NASA/Lunar Orbiter 4) • Caloris Basin - largest on Mercury (1300 km) – Few craters inside—occured near end of heavy bombardment • Similar feature seen on the western edge of the Moon—Mare Orientale. Caloris Basin (Mercury) imaged by (NASA) “This enhanced-color image of Mercury, ... shows the great Caloris impact basin, visible in this image as a large, circular, orange feature in the center of the picture. The contrast between the colors of the Caloris basin floor and those of the surrounding plains indicate that the composition of Mercury’s surface is variable. Many additional geological features with intriguing color signatures can be identified in this image. For example, the bright orange spots just inside the rim of Caloris basin are thought to mark the location of volcanic features....”

Credit: Image produced by NASA/Johns Hopkins University Applied Physics Laboratory/Arizona State University/Carnegie Institution of Washington. Image reproduced courtesy of Science/AAAS.

http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?page=1&gallery_id=2&image_id=193 Mercury’s Surface

Jumbled Opposite Scarp radial to Caloris Basin Caloris Basin on Mercury (NASA/Mariner 10) (NASA/Mariner 10) Disturbance from Caloris Basin impact propagated throughout Mercury.

Mercury’s Surface

● Mercury's surface shows many scarps or cliffs. – Unique to Mercury—not seen on Moon – Some are 3 km in height – Associated with shrinking of the crust of Mercury

● how? A 300 km long scarp or cliff on Mercury's surface (NASA/Mariner 10)

Mercury’s Surface

(from Bennett et al.) Mercury’s Volcanism

● Impact cratered spurred volcanism—spreading basalt

● Smooth plains evidence of later volcanism

● Young craters stand out because of prominent rays

– “This NAC image ... acquired during MESSENGER's third flyby of Mercury ... show large areas of Mercury's surface that appear to have been flooded by lava. In this view, craters are visible that have been nearly filled with lava, leaving only traces of their circular rims. MESSENGER images have revealed that the smooth plains in this region of Mercury's surface are quite extensive.... After the Mariner 10 mission, there was some controversy concerning the extent to which volcanism had modified Mercury's surface. Now Credit: NASA/Johns Hopkins University Applied Physics MESSENGER results, including color composite images Laboratory/Carnegie Institution of Washington , evidence for pyroclastic eruptions, and images of vast lava plains (such as shown here) have demonstrated http://messenger.jhuapl.edu/gallery/sciencePhotos/image. that Mercury was indeed volcanically active in the past.” php?page=1&gallery_id=2&image_id=372 Mercury Today

● Geologically active longer than Moon

● Volcanic/tectonic activity ended ~ 1 billion years after formation

● Dead today

Overview of Venus

● Thick clouds ● Major volcanic and tectonic activity ● Relative lack of craters ● Erosion not important ● Remains geologically activity

( Spacecraft, Arecibo Radio , NASA) Venus

● Earth's twin

● Rotates opposite direction from

● Very slow

● Thick atmosphere—surface hidden

● Extreme greenhouse effect (average temperature 740 K)

● Surface shows evidence of activity.

Distance from Sun: 0.72 AU radius: 0.95 R ⊕ mass 0.82 M ⊕ average density: 5.24 g cm-3 Venus in UV as imaged by the Pioneer composition: rocks, metal Venus Orbiter (NASA) moons: 0

Missions to Venus

● Soviet “” probes explored Venus. – – 6 were descent probes

– : atmosphere CO2

● High atmospheric pressure, Failed before reaching surface – Venera 7: new design for higher P

● Confirmed 90 bar surface pressure and 740 K surface temperature

Surface of Venus as imaged by . The compressibility of the surface was supposed to be measured by a probe extending from the , but instead it measured the compressibility of the lens cap. (this copy from http://nssdc.gsfc.nasa.gov/photo_gallery/photogaller y-venus.html) Craters on the Venusian Surface

● Magellan: ~ 1000 impact craters

● Sizes: 2 – 280 km – No really large craters / impact basins – Venus surface only ~750 million yr old (heavy bombardment?) ● No really small craters (why?)

The triple crater Stein— likely produced by the incoming body breaking apart in the Venusian atmosphere (NASA/Magellan)

Magellan image of craters ,

Aglaonice, and Saskia (NASA) Craters on the Venusian Surface

Computer generated 3-dimensional perspective view of the "crater farm" on Venus, consisting of the 37.3 km diameter Saskia in the foreground (28.6S,337.1E), 47.6 km Danilova (26.35S,337.25E) to the left, and 62.7 km Aglaonice to the right (26.5S,340E). The image was created by superimposing Magellan images in topography data, and coloring is based on and 14 Lander images. (Magellan press release P-39146)

http://nssdc.gsfc.nasa.gov/imgcat/html/object_page/mgn_p39146.html Volcanic Features

● Volcanism important

● Lava plains and volcanic – Runny lava Shield volcanoes (thinner lava) ● Some steep volcanoes http://pds.jpl.nasa.gov/planets/captions/venus/sapasmon.h tm (NASA/Magelilan) – Thicker lava ● Probably still active – No eruptions observed – Cloud composition

Pancake domes —stratovolcanoes (thick lava) (NASA/Magellan) Volcanic Features

“The hot surface of Venus shows clear signs of ancient lava flows. Evidence of this was bolstered by the robot spacecraft Magellan, which orbited Venus in the early 1990s. Using imaging radar, Magellan was able to peer beneath the thick perpetual clouds that cover Earth's closest planetary neighbor. Picture above, lava apparently flowed down from the top of the image and pooled in the light colored areas visible across the image middle and bottom. The lava cut a channel across the darker ridge that runs horizontally across the image center. The picture covers about 500 kilometers across.” http://apod.nasa.gov/apod/ap040323.html

(Magellan Project, JPL, NASA) Volcanic Features

N

A

S

A

/

J

P

L

-

C

a

l

t

e

c

h

/

E

S

A

“... volcanoes on Venus appeared to erupt between a few hundred years to 2.5 million years ago. This suggests the planet may still be geologically active, making Venus one of the few worlds in our solar system that has been volcanically active within the last 3 million years.

The evidence comes from the 's mission, which has been in orbit around the planet since April 2006. The science results were laid over topographic data from NASA's Magellan spacecraft. Magellan radar-mapped 98 percent of the surface and collected high-resolution gravity data while orbiting Venus from 1990 to 1994.

Scientists see compositional differences compared to the surrounding landscape in three volcanic regions. Relatively young lava flows have been identified by the way they emit infrared radiation. These observations suggest Venus is still capable of volcanic eruptions.” http://www.jpl.nasa.gov/news/news.php?release=2010-121 The “Tick” Crater

(

M

a

g

e

l

l

a

n

/

N

A

S

A

)

A volcano on the surface of Venus with ridges along its perimeter that give it an insect appearance Tectonics

Animation of the surface of Venus based on NASA Magellan data (Calvin J. Hamilton)

Magellan probe radar image of Venus. Here we see through the clouds. Red: high elevations (mountains); blue: low elevations (valleys) (Magellan Spacecraft, Arecibo , NASA)

One hemisphere of Venus is dominated by long bands—these are compression features in the crust. Tectonic Features of Venus

● Created via tension or compression in the crust ● No well-defined tectonic plates.

Lakshmi plains: cracks (spaced 1 – 2 km apart) created by stretching in one direction and compressing in the perpendicular direction. (NASA/Magellan) Coronae

● Concentric circular/oval features 100s – 1000s km across ● No counterpart on Earth ● Origin: Mantle plumes ● Volcanoes found near coronae.

Aine Corona (200 km diameter) (NASA/Magellan)

Geology of Venus

(from Bennett et al.) Erosion on Venus

● Thick atmosphere, but slow rotation: little erosion ● Water cannot be in or liquid form: little erosion ● Surface images show little evidence of erosion

Venera 13 Lander image of the surface of Venus, showing a composition similar to basalt on Earth (NASA) Plate Tectonics on Venus

● No evidence for plate tectonics on Venus – Surprising (why?) – Dominant reshaping force for Earth ● Venus: surface uniformly repaved ~ 750 million years ago – Tectonic/volcanic activity – Earth's surface: different ages in different locations – Perhaps plate tectonics was active before repaving? ● Why no plate tectonics? – thicker/stronger lithosphere?

– High surface T → water in crust/mantle backed out Overview of Mars

● All 4 geological processes present

● Largest volcanoes in SS

● Large tectonic canyons

● Impact craters

● Erosion features – Water still in polar ice caps and underground ice. – Perhaps liquid water underground? Mosaic of images of Mars http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=2050 (NASA) Mars

● Much smaller than Earth

● Two small moons

● Surface shows ancient volcanoes, large canyon

● Polar caps of CO2 ice and water ice

● Evidence that liquid water was once present

● Atmosphere is very thin

Distance from Sun: 1.52 AU radius: 0.53 R ⊕ Mosaic of Viking 1 images of Mars mass 0.11 M http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=2050 ⊕ (NASA) average density: 3.93 g cm-3 composition: rocks, metal moons: 2 (captured ) Terrestrial Planets

(from Bennett et al.)

Mass Radius Density Mercury 0.055 M 0.382 R 5.43 g cm-3   Venus 0.815 M 0.949 R 5.25 g cm-3   Earth 1.0 M 1.0 R 5.52 g cm-3   Moon 0.012 M 0.272 R 3.34 g cm-3   Mars 0.107 M 0.533 R 3.93 g cm-3   Map of

Topography from the orbiter Mars Global Surveyor. Spatial resolution is 15 km at the equator. (NASA/JPL)

Great differences between the Northern and Southern hemispheres remains a mystery

● North ● – Primarily low-lands – Primarily highlands – Relatively low crater count – Relatively high crater count

– Younger surface – Older surface Martian Craters

• 1000s of impact craters • Fluidized craters

Viking 1 image of a “flower” or . The ejecta features here were likely shaped by subsurface ice melted upon impact, giving it the fluidized appearance (NASA; http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=824) Viking of Arandas a 28-km “pancake” crater. (NASA) Impact Basins

● Largest—Hellas basin – 1800 km in diameter – 6 km deep – Interior covered by dust

(NASA)

Martian Volcanoes

● Volcanism important in shaping surface – Dominates in Northern highlands ● Several large shield volcanoes – largest

● Base is larger than Arizona ● 3x higher than Mt. Everest ● Rimmed by cliff (as high as 6 km)

Why can mountains grow so high on Mars? Olympus Mons: the tallest mountain in the solar system (Mars Global Surveyor Project, MSSS, JPL, NASA) Martian Volcanoes

● Bulge – Olympus Mons + several other shield volcanoes – ~ 4000 km across – How did it form? ● Still active? – Interior heat? – Impact crater density → inactive for 10s of millions of years

● Martian volcanoes may erupt again (Malin Space Science Systems, MGS, JPL, NASA) – Lithosphere thickening, dead within billions of years

Tectonics and

● Tectonic features (not plate tectonics)

● Largest: system Valles Marineris – ~ 1/5th of the planet's equator – 4x deeper than Grand Canyon ● Not caused by water or lava

– Likely connected to (Image Credit: NASA/MOLA Science Team/O. de Goursac-A. Lark) Tharsis Bulge

Water on Mars

● Erosion features present – Some features carved by water. – Rain? Underground source of water? ... ● Is there liquid water on the surface of Mars now?

● Water features? – Mars was wet in the past – Warmer T, higher P – Crater count → 2-3 billion years old Martian riverbed imaged by Mars Global Surveyor http://apod.nasa.gov/apod/ap980205.html Credit: MGS Project, JPL, NASA Overview of Earth

● Plate tectonics ● Volcanism, tectonics, erosion all important ● Erosion more important than on any other planet

(Apollo 17/NASA) http://nssdc.gsfc.nasa.gov/imgcat/html/object_page/a17_h _148_22727.html

Earth

● Only planet known to host life

● Temperature allows for liquid water

● Moon is unusually large

Distance from Sun: 1.0 AU radius: 1.0 R ⊕ mass 1.0 M ⊕ -3 average density: 5.52 g cm Earth and Moon as imaged by the Galileo composition: rocks, metal spacecraft (3.9 million miles away) http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=1879 moons: 1 (NASA) from Astronomy Picture of the Day

The Moon transiting Earth as seen from 31 million miles away. This image was taken by the EPOXI mission (Deep Impact spacecraft). (Donald J. Lindler, Sigma Space Corporation, GSFC,Univ. Maryland, EPOCh/DIXI Science Teams) Terrestrial Planets

(from Bennett et al.)

Mass Radius Density Mercury 0.055 M 0.382 R 5.43 g cm-3   Venus 0.815 M 0.949 R 5.25 g cm-3   Earth 1.0 M 1.0 R 5.52 g cm-3   Moon 0.012 M 0.272 R 3.34 g cm-3   Mars 0.107 M 0.533 R 3.93 g cm-3   Geology of Earth

● Earth exhibits all the processes we've discussed – Largest —interior still warm – Atmosphere + rotation rate + surface temperature = erosion – Volcanic outgassing created atmosphere ● Surface is shaped primarily by plate tectonics – Next chapter: plate tectonics important for climate too. – Important for life!

Plate Tectonics

● Lithosphere fractured into plates – Plates float on mantle – Plates move over, under, around one another – ~ few centimeters / year movement

(USGS; http://pubs.usgs.gov/gip/dynamic/slabs.html)

How Do We Know Earth's Surface Moves?

● Today: GPS

● Other evidence: – Past continental motion

● seem to “fit together” ● Rocks and fossils similar where Africa and S. America join – floor spreading – Difference in sea and continental crust

(from Bennett et al.)

(USGS; http://geomaps.wr.usgs.gov/parks/pltec/pangea.html) Past Continental Motion

● Mid-ocean ridges indicate seafloor spreading ● Continents move due to underlying mantle convection

Mid-atlantic ridge (NOAA) Seafloor vs. Continental Crust

● Seafloor crust thinner, denser, younger than continental crust

● Seafloor crust – 5-10 km thick – Primarily basalt (high density, runny when molten) – < 200 million years old (crater counts/radiometric dating)

● New seafloor is constantly emerging

● Continental crust – 20-70 km thick – Lower density rock (granite) – Some parts of continental crust ~ 4 billion years old

(from Bennett et al.) Seafloor Recycling

● Subduction: seafloor pushed under less dense continental crust – Trenches form – Subducted seafloor heats up, melts, erupts upward – Low density material melts first—creates continental crust

● Stratovolcanoes form

(from Bennett et al.) Seafloor Recycling

● Mid-ocean ridges: new sea floor created by rising mantle – About 2 sq. km of new seafloor produced at ridges each year – Enough to replace seafloor every 200 million years.

(from Bennett et al.) Building

● Continental crust not recycled—built over billions of years – Reshaped by volcanism, plate tectonics, erosion

Read your book for more specific examples of plate tectonic features on Earth

(from Bennett et al.) Earthquakes

● What about plates sliding sideways?

● Sideways movement → – Stresses build, produce earthquakes – Movement can be dramatic

LA and SF together in 20 million years

(from Bennett et al.) Hot Spots

● Volcanic activity outside of plate boundary – rises at hot spot

(Wikipedia/Demis) The Future

● Plates move ~ 2 cm per year ● We can project to the future

(from Bennett et al.)

How Did We Get Here?

● Small planets = cool quickly

● Plate tectonics not only due to size—Venus?

● Size, rotation, distance from Sun seems to predict outcome

(from Bennett et al.) Summary

● Terrestrial planets all looked the same when young

● Geological differences arouse due to – Size – Rotation – Distance from Sun ● This understanding allows us to predict what new planets will look like, based on knowing a few physical properties