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Home , Planetary geology, Terrestrial planet

Chapter 9 9.1 Connecting Planetary Interiors and Planetary : Surfaces and the Other Terrestrial Worlds • Our goals for learning • What are terrestrial like on the inside? • What causes geological activity? • Why do some planetary interiors create magnetic fields?

What are terrestrial planets like Seismic Waves on the inside? • Vibrations that travel through Earth’s interior tell us what Earth is like on the inside

Earth’s Interior Terrestrial Interiors • Core: Highest density; nickel and • : Moderate density; silicon, oxygen, etc. • : Lowest density; granite, • Applying what we have learned about Earth’s , etc. interior to other planets tells us what their interiors are probably like

1 Differentiation Lithosphere • Gravity pulls • A planet’s outer high-density layer of cool, rigid material to center is called the • Lower-density lithosphere material rises to • It “floats” on the surface warmer, softer • Material ends up rock that lies separated by beneath density

Strength of Rock Special Topic: How do we know what’s inside a planet? • Rock stretches when pulled slowly but • P waves push breaks when pulled matter back rapidly and forth • The gravity of a large world pulls slowly on its rocky content, shaping the world into a • S waves sphere shake matter side to side

Special Topic: What causes geological activity? How do we know what’s inside a planet?

• P waves go through Earth’s core but S waves do not

• We conclude that Earth’s core must have a liquid outer layer

2 Heating of Interior Cooling of Interior • and • Convection differentiation transports heat as when planets hot material rises and cool material were young falls • Conduction • Radioactive transfers heat decay is most from hot material important heat to cool material source today • Radiation sends energy into space

Role of Size 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

4πr2 3 surface area to volume ratio = = 4 πr3 r 3 • Smaller worlds cool off faster and harden earlier • and are now geologically “dead” • Larger objects have smaller ratio and cool more slowly

Why do some planetary interiors Sources of Magnetic Fields create magnetic fields?

• Motions of charged particles are what create magnetic fields

3 What have we learned? Sources of Magnetic Fields • What are terrestrial planets like on the inside? • A world can have – Core, mantle, crust structure a magnetic field if – Denser material is found deeper inside charged particles • What causes geological activity? are moving inside – Interior heat drives geological activity • 3 requirements: – Radioactive decay is currently main heat source – Molten interior • Why do some planetary interiors create magnetic – Convection fields? – Moderately rapid – Requires motion of charged particles inside planet rotation

What processes shape planetary 9.2 Shaping Planetary Surfaces surfaces?

• Our goals for learning • What processes shape planetary surfaces? • Why do the terrestrial planets have different geological histories? • How does a planet’s surface reveal its geological age?

Processes that Shape Surfaces Impact Cratering • Impact cratering • Most cratering – Impacts by or happened soon after • formed – Eruption of molten rock onto surface • Craters are about 10 • Tectonics times wider than object that made them – Disruption of a planet’s surface by internal stresses • Small craters greatly • outnumber large ones – Surface changes made by wind, , or ice

4 Impact Craters Impact Craters on

Meteor Crater () Tycho (Moon) “standard” crater impact into icy ground eroded crater

Volcanism and Volcanoes • Volcanism happens when molten rock () finds a path through lithosphere to the surface • Molten rock is called lava after it reaches the Runny lava makes flat Slightly thicker lava Thickest lava makes surface lava plains makes broad shield steep stratovolcanoes volcanoes

Outgassing Tectonics

• Convection of the mantle creates stresses in the crust called tectonic forces • Volcanism also releases gases from Earth’s interior • Compression forces make ranges into atmosphere • Valley can form where crust is pulled apart

5 on Earth Erosion • Earth’s continents • Erosion is a blanket term for weather-driven slide around on processes that break down or transport rock separate plates of • Processes that cause erosion include crust – Glaciers –Rivers –Wind

Erosion by Water Erosion by Ice

• Colorado River • Glaciers carved continues to the Yosemite carve Grand Valley

Erosion by Wind Erosional Debris

• Wind wears • Erosion can away rock and create new builds up sand features by dunes depositing debris

6 Why do the terrestrial planets have Role of Planetary Size different geological histories?

• Smaller worlds cool off faster and harden earlier • Larger worlds remain warm inside, promoting volcanism and tectonics • Larger worlds also have more erosion because their gravity retains an atmosphere

Role of Distance from Role of Rotation

• Planets close to Sun are too hot for rain, snow, ice and so have less erosion • Planets with slower rotation have less weather and • More difficult for hot planet to retain atmosphere less erosion and a weak magnetic field • Planets far from Sun are too cold for rain, limiting • Planets with faster rotation have more weather and erosion more erosion and a stronger magnetic field • Planets with liquid water have most erosion

How does a planet’s surface reveal History of Cratering its geological age? • Most cratering happened in first billion years

• A surface with many craters has not changed much in 3 billion years

7 Cratering of Moon Cratering of Moon • Some areas of Moon are more heavily cratered than others

• Younger regions were flooded by lava after most cratering

Cratering map of Moon’s entire surface

What have we learned? 9.3 and Mercury • What processes shape planetary surfaces? – Cratering, volcanism, tectonics, erosion • Our goals for learning • Why do the terrestrial planets have different geological histories? • What geological processes shaped our – Differences arise because of planetary size, Moon? distance from Sun, and rotation rate • What geological processes shaped • How does a planet’s surface reveal its Mercury? geological age? – Amount of cratering tells us how long ago a surface formed

What geological processes shaped Lunar Maria our Moon? • Smooth, dark lunar maria are less heavily cratered than lunar highlands

• Maria were made by flood of runny lava

8 Formation of Lunar Maria Tectonic Features • Wrinkles arise from cooling and contraction of lava flood Early surface Large impact Heat build- Cooled lava covered with crater up allows is smoother craters weakens lava to well and darker crust up to surface than surroundings

What geological processes shaped Geologically Dead Mercury? • Moon is considered geologically “dead” because geological processes have virtually stopped

Cratering of Mercury Cratering of Mercury

Caloris basin is Region opposite • A mixture of heavily cratered and smooth regions largest Caloris Basin is like the Moon on Mercury jumbled from • Smooth regions are likely ancient lava flows seismic energy of impact

9 What have we learned? Tectonics on Mercury • What geological processes shaped our Moon? – Early cratering still present – Maria resulted from volcanism • What geological processes shaped Mercury? – Cratering and volcanism similar to Moon • Long cliffs indicate that Mercury shrank early in its – Tectonic features indicate early shrinkage history

How did Martians invade popular 9.4 culture?

• Our goals for learning • How did Martians invade popular culture? • What are the major geological features of Mars? • What geological evidence tells us that water once flowed on Mars?

What are the major geological “Canals” on Mars features of Mars?

• Percival Lowell misinterpreted surface features seen in telescopic images of Mars

10 Cratering on Mars Volcanism on Mars • Mars has many large shield volcanoes

• Olympus Mons is largest in solar system

• Amount of cratering differs greatly across surface • Many early craters have been erased

What geological evidence tells us Tectonics on Mars that water once flowed on Mars?

• System of valleys known as thought to originate from tectonics

Dry Riverbeds? Erosion of Craters • Close-up • Details of some photos of Mars craters suggest show what they were once appear to be filled with dried-up water riverbeds

11 Martian Rocks Martian Rocks

• Mars rovers have found rocks that appear to have • Exploration of impact craters has revealed that formed in water Mars’ deeper layers were affected by water

Hydrogen Content Crater Walls • Gullies on crater walls suggest occasional liquid water flows have happened less than a million years ago

• Map of content (blue) shows that low- lying areas contain more water ice

What have we learned? What have we learned?

• How did Martians invade popular culture? • What geological evidence tells us that – Surface features of Mars in early telescopic water once flowed on Mars? photos were misinterpreted as “canals” – Features that look like dry riverbeds • What are the major geological features of – Some craters appear to be eroded Mars? – Rovers have found rocks that appear to have formed in water – Differences in cratering across surface – Gullies in crater walls may indicate recent – Giant shield volcanoes water flows – Evidence of tectonic activity

12 What are the major geological 9.5 Geology of features of Venus?

• Our goals for learning • What are the major geological features of Venus? • Does Venus have plate tectonics?

Radar Mapping Cratering on Venus

• Impact craters, but fewer than Moon, Mercury, Mars

• Thick atmosphere forces us to explore Venus’ surface through radar mapping

Volcanoes on Venus Tectonics on Venus

• Many volcanoes, • Fractured and including both shield contorted surface volcanoes and indicates tectonic stratovolcanoes stresses

13 Erosion on Venus Does Venus have plate tectonics?

• Photos of rocks • Most of Earth’s major geological features taken by can be attributed to plate tectonics, which show little gradually remakes Earth’s surface erosion • Venus does not appear to have plate tectonics, but entire surface seems to have been “repaved” 750 million years ago

What have we learned? 9.6 The Unique Geology of Earth • Our goals for learning • What are the major geological features of • Our goals for learning Venus? • How do we know Earth’s surface is in – Venus has cratering, volcanism, and tectonics motion? but not much erosion • How is Earth’s surface shaped by plate • Does Venus have plate tectonics? tectonics? – The lack of plate tectonics on Venus is a mystery • Was Earth’s geology destined from birth?

How do we know Earth’s surface Continental Motion is in motion?

• Motion of continents can be measured with GPS

14 Continental Motion Seafloor Crust • Idea of • Thin seafloor continental drift crust differs from was inspired by thick continental puzzle-like fit of crust continents • Dating of seafloor • Mantle material shows it is erupts where usually quite seafloor spreads young

How is Earth’s surface shaped by Seafloor Recycling plate tectonics?

• Seafloor is recycled through a process known as subduction

Surface Features Surface Features • Major geological • Himalayas are features of North forming from a America record collision history of plate between plates tectonics

15 Surface Features Rifts, Faults, Earthquakes • Red Sea is • San Andreas forming where fault in plates are pulling California is a apart plate boundary

• Motion of plates causes earthquakes

Plate Motions Hot Spots • Measurements of plate motions tell us past and future layout of continents

• Hawaiian islands have formed where plate is moving over volcanic hot spot

Was Earth’s geology destined Earth’s Destiny from birth? • Many of Earth’s features determined by size, rotation, and distance from Sun

• Reason for plate tectonics not yet clear

16 What have we learned? What have we learned?

• How do we know that Earth’s surface is in • Was Earth’s geology destined from birth? motion? – Many of Earth’s features determined by size, distance from Sun, and rotation rate – Measurements of plate motion confirm idea of continental drift – Reason for plate tectonics still a mystery • How is Earth’s surface shaped by plate tectonics? – Plate tectonics responsible for subduction, seafloor spreading, , rifts, and earthquakes

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