110 Announcements: Chapter 7 • Reading for tomorrow: pp. 211 – 233 and the Terrestrial Worlds • Midterm next Monday

• Observing tomorrow at Kapiolani Park (8pm, mauka side)

Mercury craters volcanoes smooth , few craters cliffs

Radar view of a twin- peaked some craters volcanoes riverbeds? craters smooth plains

7.1 Earth as a Earth Our Goals for Learning • Why is Earth geologically active? volcanoes • What processes shape Earth’s craters surface? mountains • How does Earth’s affect riverbeds the planet? Why is Earth geologically active? Internal structure, by rock strength Short answer: the Earth is big enough to still have a hot interior. The “lithosphere” is the cool rigid rock that Internal Stucture, by : forms a planet’s outer layer: the and • Core – high density central region (mostly nickel and some of the . metals) • Mantle – medium density, rocky material in the The lithosphere floats on middle of the planet the lower layers. • Crust – thin outer layer, lowest density (granite and basalt)

Internal Structure of the Terrestrial Sources of Internal Heat 1) Gravitational of accreting 2) Differentiation 3) Radioactivity

The thickness of the lithosphere controls many geological processes. Differentiation What cools off faster?

• Layers ordered by density A. A grande-size cup of Starbucks coffee • Highest density on the bottom B. A teaspoon of capuccino in the same cup. • sorts materials by density. (Just like oil and separating—oil is less dense, so it floats on top of water)

• Differentiation converts gravitational potential energy to heat.

What cools off faster? What cools off faster?

A. A grande-size cup of Starbucks coffee A. A big . B. A teaspoon of capuccino in the same cup. B. A tiny terrestrial planet. What cools off faster? Heat Drives Geological Activity

A. A big terrestrial planet. Convection: hot rock B. A tiny terrestrial planet. rises, cool rock falls.

1 cycle takes 100 Why? million years on Earth.

Larger planets retain their heat longer than smaller ones because there is more material—more insulation.

A large planet… Comparing the Planets

• Is still warm inside • Has a convecting mantle • Has a thinner, weaker lithosphere • Has molten rock nearer the surface which makes it more geologically active Which planets have the most and least geological activity? Planetary magnetic fields Earth’s

Earth’s magnetic fields protects us from charged particles from the The charged particles can create the aurora (“Northern lights”) Moving charged particles create magnetic fields. So can a planet’s interior, if the core is electrically conducting (metal), convecting (liquid), and rotating

If the planet core is , do you If the planet core is cold, do you expect it to have magnetic fields? expect it to have magnetic fields?

A. Yes, refrigerator magnets are cold, and they A. Yes, refrigerator magnets are cold, and they have magnetic field. have magnetic field. B. No, planetary magnetic fields are generated B. No, planetary magnetic fields are by moving charges around, and if the core is generated by moving charges around, and cold, nothing is moving. if the core is cold, nothing is moving. How do we know what is inside How do we know what is inside the Earth? the Earth? A. We can drill deep inside the Earth. A. We can drill deep inside the Earth. B. We can use optical fibers to see deep inside B. We can use optical fibers to see deep inside the Earth. the Earth. C. X-ray machines allow us to view the inside C. X-ray machines allow us to view the inside of the Earth. of the Earth. D. Seismic waves generated by earthquakes D. Seismic waves generated by earthquakes probe the Earth’s interior. probe the Earth’s interior.

What processes shape Earth’s surface? 1. Impact Cratering 1) Impact cratering 2) Volcanism 3) Tectonics 4) Erosion 1. Impact Cratering 2. Volcanism • Moon must be hit as often as Earth. Molten rock rises when it is: • Where are Earth’s • Less dense than its craters? surroundings. • Squeezed by its surroundings. • Erased by volcanic • Pushed by expanding activity and erosion. trapped gas (, CO2, N2, H2S, SO2) The more craters, the older the surface

Why doesn’t Mars have as much 2. Volcanism volcanic activity as Earth? • Erases other geological features A. It’s too far from the Sun, so it cooled off • Provided gas for our faster. atmosphere (esp. N2) B. It’s smaller than the Earth, so it cooled off • Provided water for our faster. oceans C. It might, we just haven’t seen them erupt yet. Why doesn’t Mars have as much 3. Tectonics and Plate Tectonics volcanic activity as Earth? Tectonics: any surface reshaping from / A. It’s too far from the Sun, so it cooled off stresses on the lithosphere faster. B. It’s smaller than the Earth, so it cooled off Internal Heat Required! faster. Plate tectonics: pieces of lithosphere moving C. It might, we just haven’t seen them erupt yet. around

Only Earth has plate tectonics.

3. Tectonics on the Terrestrial Planets 4. Erosion Earth • Wearing down or building up of geological features by wind, water and (weather) • Important process on Earth – Strong winds (due to Earth’s rapid ) also had tectonics when it was much younger, – Lots of water (from but it resulted only in compression, not stretching. Hot volcanism) core cooled off and the whole planet shrunk in size.

Generally, tectonics go hand-in-hand with volcanism. How does Earth’s atmosphere How does Earth’s atmosphere affect the planet ? affect Earth?

1) Erosion (already mentioned) 2) Protection from radiation 3) Changes the surface : greenhouse effect 4) Makes the sky blue!

The Greenhouse Effect Radiation Protection

• All X-ray light absorbed very high in the atmosphere. • light

absorbed by ozone (O3)

How does the greenhouse effect alter surface temperature? Greenhouse A Greenhouse Gas effect:

Certain • Any gas that absorbs molecules let through but trap • Greenhouse gas: molecules with 2 different types of escaping elements (CO2, H2O, CH4) infrared photons • Not a greenhouse gas: molecules with single or 2 (H2O, CO2, CH4) atoms of the same element (O2, N2)

Greenhouse Effect: Bad? What have we learned? • Why is Earth geologically The Earth is much warmer because of the active? greenhouse effect than it would be without an • Internal heat drives atmosphere…but so is Venus. geological activity. – Larger the planet, more heat retained. !Earth’s surface temperature would be – mantle convection and thin below freezing without the greenhouse lithosphere = active surface effect. geology – Circulation of liquid outer core creates Earth’s magnetic field. 7.2 Mercury and the Moon: What have we learned? Geologically Dead • What processes shape Earth’s surface? – Impact cratering • Our Goals for Learning – Volcanism • Was there ever geological activity on the • Atmosphere and Oceans due to – Tectonics Moon or Mercury? – Erosion • How does Earth’s atmosphere affect the planet? – protects the surface from dangerous solar radiation – the greenhouse effect, without which the surface temperature would be below freezing.

Moon Mercury

• Some volcanic activity 3 billion years ago (heat due to ) must have flooded lunar craters, creating lunar maria. • Plenty of craters - including a huge ‘basin’ • The Moon is now geologically dead. • Smooth plains from volcanism

• Only current activity is “sandblasting” by . • Steep cliffs – evidence of past tectonics Did Mercury shrink? What have we learned?

• Was there ever geological activity on the Moon or Mercury? • Yes - both the Moon and Mercury had some volcanism and tectonics when they were young. • Small sizes, however, caused their interiors to Steep long cliffs formed when the core cool quickly cooled, shrinking the planet by ~20 km. • Now geologically dead. Mercury is now geologically dead.

7.3 Mars: A Victim of Planetary Mars vs. Earth Freeze-drying • 50% Earth’s radius, 10% Earth’s • Our Goals for Learning • Axis tilt about the same as Earth. • What geological features tell us that water • Similar . once flowed on Mars? • is more elliptical than Earth’s: seasons • Why did Mars change? more extreme in the south than the north.

• Thin CO2 atmosphere: little greenhouse What geological features tell us water once Martian Winds flowed on Mars?

• Cause the pale pink color of the sky Too cold for liquid water • Also causes dust devils now, and too low.

http://marsrovers.nasa.gov/home/index.html

Surface of Mars appears to have ancient river beds

Eroded crater

Condition of craters indicates surface history Volcanoes…as recent as 180 million years ago… Past tectonic activity…

Opportunity

Low-lying regions may once have had oceans Why did Mars change? Today, most water lies frozen underground (blue regions)…

Some scientists believe accumulated snowpack melts to carve gullies even today

Most water lost to space forever…