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The habitability of Earth Tuesday, September 24, 2013 Outline of today’s class To learn about the history of life on Earth, we need to learn the history of the Earth. What makes the Earth suitable for life? Water + organics + stability. Volcanism, magnetic fields, plate tectonics: geological activity. Atmosphere The question becomes ‘should we be looking for geologically active worlds in the Solar System?’ Tuesday, September 24, 2013 Worlds in the inner Solar System Tuesday, September 24, 2013 What Makes the Earth Habitable? Distance of Earth from Sun (not too close, not too far) Liquid water Surface gravity Atmosphere Magnetic field Solid surface Building blocks of life Climate suitable for life Plate tectonics Tuesday, September 24, 2013 The Rock Cycle Tuesday, September 24, 2013 Strata in Sedimentary Rocks Tuesday, September 24, 2013 Strata on Mars Tuesday, September 24, 2013 Endurance Crater on Mars: photo by Opportunity Rover Grand Canyon Strata Tuesday, September 24, 2013 Example on Mars: you can get relative ages easily (e.g., mountains, plain, meteor impact) Tuesday, September 24, 2013 Atomic Numbers, Isotopes, etc. Tuesday, September 24, 2013 Radioactive Decay Tuesday, September 24, 2013 Half-life Tuesday, September 24, 2013 Fossils in Rocks (aged) allow us to study development of life through geologic ages Tuesday, September 24, 2013 The Geological time scale Tuesday, September 24, 2013 Review Questions Chapter 4 (p147) : Discuss if these statements make sense. Q23. The most common type of rock in the Grand Canyon is sedimentary. Q25. If you had a time machine that dropped you off on Earth during the Hadeon eon, you’d most likely be killed by a large meteor impact. Q21. Palentologists will find the fossil remains of almost every human being who ever lived. Tuesday, September 24, 2013 How Old is the Earth? It must be older than the oldest minerals found on Earth (4.4 Gyr old) zircon found in Australia It must be older than the oldest Moon rocks (4.4 Gyr old) the Moon formed after the Earth in the solar nebula hypothesis (next) It must be younger than the oldest meteorites (4.57 Gyr old) Scientists estimate that the Earth is about 4.54 Gyr old Tuesday, September 24, 2013 Formation of the Moon The Moon is thought to have formed very soon after the Earth formed within 50-150 Myr It is thought to have formed from the collision of a Mars-sized object very early on same composition & density as Earth’s crust thus formed after differentiation of Earth’s core (at 50-150 Myr) Tuesday, September 24, 2013 Heavy bombardment on the Moon The surface of the Moon preserves a record of ancient impact craters The lunar maria exhibit relatively few craters this evidence has been erased on the Earth these surfaces are younger, about 3.0-3.9 Gyr old Most impacts on Earth must therefore have occurred during the Hadean era Tuesday, September 24, 2013 Life during the Hadean era Radiometric dating of zircons indicates that Earth’s crust had already formed 4.5 Gyr ago This implies that the Hadean Earth may have been habitable at that time Although frequent impacts may have sterilized the Hadean Earth sufficiently large impacts could have vaporized all of Earth’s oceans! Tuesday, September 24, 2013 Earth’s Interior Once the surface forms, then the interior of Earth has several important effects on the surface Volcanoes have built up much of the atmosphere Plate tectonics have shaped the continents Earth’s magnetic field shields life from the solar wind Tuesday, September 24, 2013 Plate Tectonics Earth’s surface is broken up into plates which float on the mantle and move around slowly Movement of these plates is responsible for mountain building sea floor spreading earthquakes volcanic hot spots subduction rift valleys continental drift Tuesday, September 24, 2013 Plate Tectonics at Work Tuesday, September 24, 2013 Building Earth’s Atmosphere and Oceans Earth’s atmosphere and oceans were produced by several mechanisms Outgassing (e.g. by volcanoes) of gases trapped within the Earth ** Material deposited during impacts (including ice and minerals from comets) Life! Tuesday, September 24, 2013 The Greenhouse Effect Greenhouse gases in the Earth’s atmosphere make the Earth considerably warmer than it would otherwise be This is a good thing for life, since it allows liquid water to survive on Earth’s surface However, by adding manmade greenhouse gases, we are now starting to warm the atmosphere further Tuesday, September 24, 2013 The Snowball Effect Greenhouse warming has not been perfect e.g., ice ages (longest and deepest were ~2.3 Gyr and 700 Myr ago) occur when Earth’s rotation axis tilt varies (22 to 25 deg) and depend on continental motions, making seasons more or less extreme Tuesday, September 24, 2013 Earth’s Carbon Dioxide Thermostat Tuesday, September 24, 2013 How to Lose an Atmosphere Several mechanisms can lead to the loss of part or all of a planetary atmosphere thermal escape (gas molecules move too fast compared to gravitational attraction) impact-triggered escape solar wind stripping Tuesday, September 24, 2013 Movies of Aurorae & Solar Storms!! Hi all - here are the links that I would have liked to show you in class. this is amongst the best footage of aurora that I have seen: http://www.youtube.com/watch?v=WL_-Zz7JDoA this is amazing footage of solar flares and storms http://www.youtube.com/watch?v=wFb7OZx2NYo http://www.youtube.com/watch?v=t3A5C91M17A Hubble Space Telescope images of aurora on Jupiter http://www.youtube.com/watch?v=oFsoXjFoKf4 Hubble images of aurora on Saturn http://www.spacetelescope.org/videos/heic1003d/ And here is a fairly recent article on aurora outside the solar system! http://www.zmescience.com/space/astrophysics-space/ aurora-outside-solar-system-22012013/ Tuesday, September 24, 2013 What Makes the Earth Habitable? The size/mass of Earth Earth’s distance from the Sun Geologic Activity (Volcanoes, Plate tectonics) Impacts: not too many, not too few Earth’s magnetic field The stabilizing effect of the Moon Earth’s atmosphere and greenhouse effect Tuesday, September 24, 2013 Next week Try Chapter 4 review questions Qs #1, 5, 6, 8, 9, 10, 15, 16, 20, and 21-30. example Q15: What are the 3 requirements for a planetary magnetic fileld and how does the EArth meet these? How does the magnetic field protect our atmosphere? Skim Chapter 5 Assignment #2 is available on the website. Friday class is cancelled. Tuesday, September 24, 2013