Chapter 9 part 1

Planetary Processes Connecting planets’ interiors and surfaces • Terrestrial planets all formed at the same time from the same basic materials…but only can support life. • Even though they formed under similar conditions, they’re all very different. • How did these differences come to be? Connecting planets’ interiors and surfaces • Terrestrial planets all formed at the same time from the same basic materials…but only Earth can support life. • Even though they formed under similar conditions, they’re all very different. • How did these differences come to be? What are the terrestrial planets like on the inside? • Information about Earth’s interior comes from seismic waves produced by earthquakes. • Information about other planets comes from an understanding of Earth’s interior, combined with other clues. P and S waves

• P waves: result from compression and stretching • S waves vibrate up and down. • Liquid Earth layers bend P waves and stop S waves. Layering by density

• All terrestrial worlds have layered interiors. – Core: Highest-density material, consisting of metals such as Fe and Ni. – Mantle: Rocky material of moderate density—mostly minerals that contain Si, O, and other elements. – : Lowest-density , such as granite and basalt. Inside the terrestrial planets Layering by strength • Rock is not all the same. • Different kinds of rock have different properties. • These differences lead to layers within the crust and mantle that account for volcanoes, earthquakes, and other geologic processes. • Smaller bodies () don’t have enough to overcome the inherent strength of the rock, and remain oddly-shaped. • Larger bodies (planets) with larger gravity are able to deform the rock and become more spherical. • Like silly putty, rock is more easily deformed if shaped slowly over time. Rock breaks if suddenly impacted. What causes geological activity?

• Geological activity: how much change is going on at the planet’s surface. • Interior heat is the primary driving force. – Causes the volcanoes and earthquakes that change the appearance of planetary surfaces. Why planetary interiors are hot • Accretion deposits energy brought in by colliding planetesimals. • Differentiation converts gravitational into thermal energy. • Radioactive decay . When radioactive nuclei decay, subatomic particles are released and interact with surrounding atoms and heat them up. Cooling of planetary interiors

• Cooling a planetary interior requires transporting heat outward. • Convection: Heat is transported up and cooler material sinks. • Conduction: Hot material transfers heat to cool material through contact. • Radiation: Objects can lose heat by emitting thermal radiation, and are always losing heat to space. Why do some planetary interiors create a magnetic field? • Three basic requirements for a global magnetic field: – An interior region of electrically conducting fluid (liquid or gas) such as molten metal. – Convection in that layer of fluid. – At least moderately rapid rotation. Sources of magnetic fields Shaping planetary surfaces

• Impact cratering • • Tectonics • Impact cratering

• forms when an slams into an object with a solid surface. • Debris from the impact rains down over a large area • Craters are generally circular and are about 10 times as wide as the objects that created them, and 10 – 20% as deep as they are wide. Craters Three craters on Volcanism • Volcanism refers to any eruption of molten onto the surface. • Occurs when magma finds a path through the lithosphere to the surface. • Molten rock rises for three reasons: – Molten rock is less dense than surrounding rock. – Magma chambers may be squeezed by surrounding rock, forcing the magma upward – Magma often contains compressed gasses that expand as it rises. Volcanoes Tectonics

• Tectonics: surface reshaping resulting from stretching, compression, or other forces acting on the lithosphere. Erosion Chapter 9 part 2

Why do the terrestrial planets have different geological histories? Why do the terrestrial planets have different geological histories?

Small planets cool more quickly and do not end up with atmospheres, tectonics, or strong magnetic fields. Why do the terrestrial planets have different geological histories?

Planets closer to the are hotter, have no rain, snow, or , and no erosion, hotter temperatures means that atmospheric gasses escape more easily.

Moderate temps allow for ice, rain, oceans, lakes (and erosion). Gravity can hold at- mospheric gasses.

Low temps lead to ice and snow, but no rain (limited erosion) atmosphere is thick. Why do the terrestrial planets have different geological histories?

Slow rotation: less wind, less erosion, weak magnetic field.

Rapid rotation: more wind, more erosion, stronger magnetic field. Geology of and the

• Considerably smaller than Earth, Mars, and Venus. – Lost most of their internal heat • =no energy source to power geological activity – Lack significant atmospheres • gravity too low to hold atmospheres, • no volcanics = no “outgassing” to replenish lost atmosphere. Geology of Mercury and the Moon

• Most obvious surface features are impact craters. • Cratering is the most important geological process on both worlds. • There are a few tectonic features that indicate past geological activity. What geological processes shaped the moon? • Impact cratering – Lunar highlands (light areas) are heavily cratered • Volcanism and tectonics – Lunar maria (dark areas) were made by a flood of thin molten lava that flowed like rivers. – Features within maria are surface wrinkles caused by small scale tectonics. Formation of Lunar Maria Features within the Maria The Moon Today • Moon is longer geologically active (geologically dead for over 3 billion years.) • Surface is desolate and nearly unchanging. • Surface is being “sandblasted” by small impacts (micrometeorites). What geological processes shaped Mercury? • Impact craters: visible everywhere on Mercury (surface is ancient) • Mercury’s craters are less crowded than those on Moon (lava covered up some of Mercury’s craters in the past) • Mercury’s mantle was once partly molten. • Mercury probably had dsome volcanism at one time. What geological processes shaped Mercury? • Caloris Basin: – Largest single feature on Mercury’s surface – Covers more than ½ of mercury’s radius. • Most surprising feature: – Enormous cliffs caused by cooling of Mercury’s interior. Formation of Mercury’s Cliffs

• Mercury’s core and mantle shrank as it cooled • Surface cracked, forming the cliffs. • Contraction probably closed off all volcanic vents, ending Mercury’s volcanism. Major geologic features of Mars • Total surface area is ~¼ that of Earth, but both planets have the same land area • Impact cratering – Southern hemisphere: high elevation, scarred by large craters (Hellas Basin) – Northern : low elevation and fewer craters Major geologic features of Mars • Volcanism – Most important process for erasing craters on Mars – Several shield volcanoes • Olympus Mons is the largest in the . Major geologic features of Mars • Volcanism – Olympus Mons’ peak is 26 km above the surface (3 times as tall as Mount Everest.) – Tharsis Bulge: region of upwelling due to a large mantle plume. Major geologic features of Mars

Tectonics • Valles Marineris extends over 1/5 of the way along the planet’s equator. • As long as the US is wide and 4 times as deep as the grand canyon. Evidence for water once flowing on Mars • Features that look like dry riverbeds • Channels that appear to have been carved by running water – Must have been caused by water because: – water was the only substance that could have been liquid in Mars’s past – Also the water is the only substance that could have been abundant enough. Chapter 9 part 3

Geology of Venus and Earth Similarities between Venus and Earth • Even though the atmosphere of Venus is very dense, hot, and is under a lot of pressure, beneath the surface, Venus is quite similar to Earth. • Venus and Earth are nearly the same size (Venus’s radius is 5% smaller.) • Venus and Earth are close together in the solar system: formed from the same types of planetesimals. • Venus and Earth have similar densities, so probably have similar compositions. • Because they are about the same size and of about the same composition, they probably have about the same level of internal heat. • *we still see differences in their geology* Surface of Venus Surface features of Venus

• Scientists have used “radar mapping” to study the surface of Venus. • Biggest features on the surface are the 3 “Terra.” • Has few impact craters • Surface is about 750 million years old. • Volcanism is very important on Venus…surface shows many lava plains and volcanic . (still active) Surface features of Venus

• Tectonics are important on Venus: • Surface fractures, “coronae,” volcanoes. No erosion on Venus

• BIGGEST DIFFERENCE between Venus and Earth is the lack of EROSION on Venus. – Venus is too hot to have any rain or snow. – Rotation is too slow to have wind or weather. No on Venus

• Almost all of the features on Earth’s surface are due to plate tectonics, but the surface of Venus shows no evidence for this feature. • Venus has another type of surface process: “Repaving”. – Entire surface is about 750 million yrs old. • Earth’s surface has fractured into plates that move across the surface due to mantle convection. • Venus MAY have a thicker, stronger lithosphere that doesn’t fracture. Geology of Earth • Earth’s size explains why it retains internal heat and has tectonics and volcanics. • Earth’s rotation and distance from the sun explain why it has erosion by wind and water. • Earth’s size and distance from the sun explain why we have an atmosphere. (Volcanic outgassing and retention of atmospheric gasses.) Surface of Earth: Plate tectonics Plate tectonics Plate tectonics: Scientific theory that explains how Earth’s surface geology results from the slow motion of continental “plates”. – Lithosphere cracked due to stresses of mantle convection. – Lithospheric plates “float” on the mantle and gradually move over, under, around each other as the mantle convects. – Rate of motion is a few cm / year. – (we don’t notice the motion, but it can be tracked using GPS.) Continental Motion • Older theory is called “continental drift”. (continents were thought to float freely on solid rock beneath them.) • Evidence for continental motion: – Puzzle-like fit of continents. – Similar fossils on coastlines of distant continents. Seafloor spreading

• Seafloor spreading is the “mechanism” for plate tectonics. • Explains how the continents move apart over time. • Mid-ocean ridges are places where new crust is being formed and pushing apart the sea floor on either side. Plate tectonics and seafloor spreading Seafloor crust and Continental crust • Earth’s surface has two types of crust: – Seafloor: • Denser (basalt) • thinner (5-10 km thick), • younger (>200 million yrs old) – Continental • Composed of granite • 20-70 km thick • Up to 4 billion yrs old How surface is shaped by tectonics Continent building

• Continents are built by the pile-up of continental crust and shaped by volcanism, tectonics, and erosion. – Volcanic mountains – Sedimentary rocks – Islands accreted onto the coastlines – Mountains formed from collisions with other continents. building

• Himalayas are being formed by the collision of two continental plates Continental Rifting

• Red sea was formed by the spreading apart of two continental plates. Earthquakes caused by the sliding of two plates • San Andreas fault is a zone where two plates are sliding past each other. Result of an earthquake Formation of volcanic islands

• Hawaiian islands formed by the passing of continental crust over a “hot spot.” Plate tectonics over time

Earth’s surface has changed dramatically over time. Geological histories of the terrestrial worlds