Lecture 9 - Earth - Interior and Surface Activity

Lecture 9 - Earth - Interior and Surface Activity - Earth...

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Unformatted text preview: Earth: Interior and Surface Activity ASTRONOMY 3 Lesson 9 1 The relief globe in the Field Museum in Chicago represents Earth's topography - see http:// en.wikipedia.org/wiki/Geology NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Review of Lesson 8 Gravitational forces by the Sun and the Moon are responsible for the tides observed on Earth. Earth has two tidal bulges, one on the side facing the Moon and one on the opposite side. Tidal forces from the Earth on the Moon have forced the Moon into tidal locking. The Moon is always facing the same side to Earth. The Moon's rotation period is the same as its orbital period around Earth. The Moon most likely formed in a collision of a Mars-sized proto-planet with the proto-Earth. This explains the low density of the Moon compared to the average density of the terrestrial planets. 2 NATURE of the Universe Questions from Lesson 8 Astronomy - Earth: Interior and Surface Activity Think about (questions from Lesson 8): Where does the heat in Earth's core come from? How do we know about the structure of Earth's interior? 3 NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Today's Topics Earth's Interior (Ch. 5.4) Plate Tectonics (Ch 5.5) Earthquakes (Ch 5.5) Summary & Homework Extra Credits & Review of Homework 2 4 NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Thickness of Earth's crust in km Earth's Interior Deepest drillings: 10 to 12 km (0.2% of Earth's radius), i.e. they barely scratch Earth's crust. Crust Mantle Core How can we look deeper into Earth's interior? 5 NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Earth's Interior Earthquakes produce seismic waves, which travel through Earth and enable us to probe the interior. There are two kinds of seismic waves: P-waves travel faster than S-waves, and hence arrive earlier at the measurement station. 6 NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Earth's Interior Two kinds of waves: P-waves ("primary" or "pressure"), which are like sounds waves. S-waves ("secondary" or "shear") waves. Shear waves cannot travel through liquids. Seismic waves travel faster in denser material, i.e. we can use them to estimate the density of material in Earth's interior. 7 NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Earth's Interior The Hawaiian 6.7 mag earthquake observed by various seismic stations across the USA. (Washington) (New Hamphire) 8 NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Earth's Interior The Hawaiian 6.7 mag earthquake observed by various seismic stations across the USA. (Washington) xx quake 1 P-waves S-waves (New Hamphire) 9 NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Earth's Interior Comparison of arrival times of P- and S-waves at different seismic stations enables us to pin-point the center of the Earthquake. By measuring the seismic waves from one Earthquake event on different places on Earth, we can also construct a model of Earth interior. 10 NATURE of the Universe Astronomy - Earth: Interior and Surface Activity In 1936, the Danish seismologist Inge Lehmann concluded that Earth has an inner, solid core, which deflects P-waves, and which is surrounded by an outer, liquid core. Earth's Interior Travel time and shadow zone for the Hawaii earthquake. 11 NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Earth's Interior density Iron Nickel 7,874 kg/m3 8,908 kg/m3 Earth Crust 3,000 kg/m3 Cores is rich in Iron and Nickel, and is compressed to densities of 12,000 kg/m3 by pressure from Earth's upper layers. 12 NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Earth's Interior The mantle has a much lower density than the core. Its composition can be analyzed from volcanic lava samples. Earth's mantle is rocky and consists of basalt, similar to the low-lands on the Moon. 13 NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Where do Earthquakes come from? Plate Tectonics Earth's crust is a patchwork of plates Most earthquakes (and volcanoes) are at the plate boundaries. 14 The map can be found at http://denali.gsfc.nasa.gov/dtam/seismic/ NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Why is Earth's interior hot? Plate Tectonics Heat left over from the formation of Earth, supplemented by radioactive decay of 40K. 40K is a naturally occurring isotope of potassium with a half-life time of 1.25 billion years. The heat from Earth's interior is transported to the surface by convection: hot material is rising, giving off its heat, and colder material is sinking down. 15 NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Plate Tectonics This is the "engine",which also drives the movement of Earth's plates. The heat from Earth's interior is transported to the surface by convection: hot material is rising, giving off its heat, and colder material is sinking down. 16 NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Directions of the movement of tectonic plates Plate Tectonics Plates move with respect to each other. Friction at the plate's boundaries causes these movements to be episodic rather than continuous and smooth. Sudden plate movements result in earthquakes. 17 NATURE of the Universe Astronomy - Earth: Interior and Surface Activity How did the world look 200 million years ago? Alfred Wegener (1912): Fossil and geological evidence can be used to trace back the movement of the continents. Plate Tectonics 18 NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Plate Tectonics 19 See http://jan.ucc.nau.edu/~rcb7/global_history.html for more details and more maps. NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Plate Tectonics About 260 million years ago, all the landmasses on Earth formed one "supercontinent" called Pangaea. This supercontinent subsequently broke up into todays continents. 20 NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Where do we go from here? The formation of new rift valleys... Plate Tectonics Earth - 250 million years into the future. The formation of another supercontinent... 21 Simulation be Chris Scotese (UT) - see http://earth.rice.edu/mtpe/geo/geosphere/topics/ plate_tectonics/plate_future.html NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Earthquakes The San Andreas fault runs 1,300 km (800 miles) through California and marks the boundary between the Pacific plate (west) and the North American plate (east). 22 The handbook on Earthquake Safety "Putting Down Roots in Earthquake Country" can be viewed online or ordered (at no cost) from http://www.earthquakecountry.info/roots/ roots.html It is available in English and Spanish. NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Earthquakes The southern section of the San Andreas fault is building up "elastic strain" at a rate of 25 millimeter (1 inch) per year. Since the last major earthquake here happened more than 300 years ago, a corrective movement of 6 to 8 meters is expected. Yuri Fialko (UCSD) Simulations of ground-shaking (velocity) of a hypothesized future rupture of the southern San Andreas fault by Yuri Fialko (UCSD). 23 See http://sioviz.ucsd.edu/~fialko/ for more details on the research. NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Earthquakes What would the impact of a 6.7 mag earthquake be in L.A.? The Northridge earthquake in 1994 was 6.7 mag. 24 NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Freeways... Earthquakes Apartment building in San Fernando Valley Dorm in Sunset village 25 NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Get up to speed on earthquake safety! Earthquakes http://www.earthquakecountry.info 26 NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Summary Summary: Earth - Interior and Surface Activity Seismic waves enable us to probe Earth's interior structure. Earth consists of a high-density iron-nickel core, a mantle made of basaltic material, and the crust. Earthquakes originate at the plate boundaries and can be traced back to the relative movement of plates with respect to each other (plate tectonics). The driving force for plate tectonics is heat from Earth's interior, which gets transported to the surface by convection. 27 NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Homework Homework Reading assignment: Chapter 5.3 Homework 3 is online. Due date is Mo, Oct 23 at 12:00 pm (noon) Think about: How does a greenhouse work? Is the greenhouse effect good or bad? 28 NATURE of the Universe Astronomy - Earth: Interior and Surface Activity Extra Credits Extra Credits Tonight is again an opportunity of planetarium visit and telescope viewing (form on the class web page or in front of my office) Remember to turn in your completed forms! Essay: There will be some mild (fairness) grading In general I will try to award 1.5% extra credits for each essay submitted 0.5% to 1.0% might be subtracted if the essay falls significantly short of 1,500 words (1,200 or less) and/or if turns out to be simply copy&paste from another essay or online resources. content/your conclusions will not affect the grade 29 NATURE of the Universe Astronomy - The Solar System Homework Review Review of Homework 2: dose of statistics Distribution of scores 100 75 50 25 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Question Percentage of correct answers Median: 13 correct answers Mean: 12 correct answers Questions #6, #10, #13 and #14: less than 80% correct answers 30 Answer key to homework 2 is available at http://web.physics.ucla.edu/class/06F/ 3_BRANDNER/homework/index.html - select "Homework 2" and then "key". NATURE of the Universe Astronomy - The Solar System Homework Review Review of Homework 2 6. Mars, Jupiter, and Saturn show Retrograde Motion because Earth moves faster in its orbit compared to the outer planets 10. If the Sun would be twice as hot, but keep its current size, its energy output would ... increase by a factor of 16. According to Stefan's law, the energy output per area scales with the fourth power of the temperature. If the temperature increases by a factor of 2, the energy output increases by 24 = 2*2*2*2 = 16 31 NATURE of the Universe Astronomy - The Solar System Homework Review Review of Homework 2 13. In general, the spectral lines of molecules are more complex than those of atoms. Atomic Hydrogen Molecular Hydrogen (H2) 14. According to Bohr's model of the atom, electrons only make transitions between distinct orbits. This explains why atoms emit or absorb light only at very specific wavelengths! 32 ...
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This note was uploaded on 10/13/2008 for the course ASTR 3 taught by Professor Hauser during the Fall '07 term at UCLA.

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Lecture 9 - Earth - Interior and Surface Activity - Earth...

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