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Prof. Miller's Astronomy 1 lecture notes on Earth

Prof. Miller's Astronomy 1 lecture notes on Earth

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  • 1. Earth’s Geology LACC: §7.2, 3, 4 • Understand Earth’s interior: core (inner and outer), mantle, crust. • Understand Earth’s geological features • Understand Earth’s some of the Earth’s extinction events. An attempt to answer the “big question”: what is out there? Wednesday, March 3, 2010 1
  • 2. Earth’s Interior Wednesday, March 3, 2010 2
  • 3. Earth’s Interior Wednesday, March 3, 2010 3
  • 4. Earth’s Interior Seismic waves travel at about 10 km/ sec and, from mapping of the timing and type of wave around the globe, we are able to map the interior of the Earth. Changes in refraction of seismic waves are due to sharp changes in the density = discontinuities due to chemical composition. The result is that we know that the interior of the Earth has 4 components: • a thin crust of density 3.3 gm/cc composed of metals, silicates (a substance called basalt) • a semi-solid mantle of density 3.5 to 5.5 gm/cc composed of olivine Fe oxides • a liquid outer core of density 9 to 11 gm/cc composed of molten Fe • a solid inner core of density 17 gm/cc composed of Fe and Ni. Wednesday, March 3, 2010 4
  • 5. The Earth: Interior Heat A cross-section of the Earth reveals.... a thin, hard crust ranging from 10 to 100 kilometers thick.... a donut-shaped mantle 2,900 kilometers thick. Instead of dough, it consists of viscous molten rock that flows very slowly, on a geological time scale. "It moves about as fast as your fingernails grow," Marone explains.... a two-part core. "The inner part is about the size of our moon," Marone says, "and has a density of essentially steel." The outer core surrounding it is an ocean of liquid metal 2,300 kilometers thick. the vast majority of the heat in Earth's interior—up to 90 percent —is fueled by the decaying of radioactive isotopes like Potassium 40, Uranium 238, 235, and Thorium 232.... Wednesday, March 3, 2010 5
  • 6. The Earth: Tectonic Plates Earth is the largest terrestrial planet; therefore, it is taking the longest to cool. It’s crust (Si, O, Fe, Al, Mg; 3 g/cm3) is broken up into >12 sections called tectonic plates which are floating on a convecting mantle. The interior is hot due to (accretion, differentiation, and) radioactive decay. Significant erosion keeps Earth’s surface young-- a few hundred million years old. (The oldest rocks are 3.9 billion years old. All the planets formed 4.5 billion years ago.) Wednesday, March 3, 2010 6
  • 7. The Earth: Tectonic Plates 5:17 The Early Earth and Plate Tectonics Wednesday, March 3, 2010 7
  • 8. Hot Spots ...the Hawaiian Island and the seamounts that extend from Hawaii to the Aleutian trench show the movement of the Pacific plate as it moved over the hot spot. Radiometric dating shows that the volcanic activity decreases in age toward the island of Hawaii, which is now over the hot spot. Wednesday, March 3, 2010 8
  • 9. The Earth: Impact Craters Current total number of confirmed impact structures: 176 Wednesday, March 3, 2010 9
  • 10. The Earth: Arizona Impact Photograph by David Roddy, United States Geological Survey. Wednesday, March 3, 2010 10
  • 11. The Earth: Arizona Impact Meteor Crater in Arizona is one of the best known examples of an impact crater on Earth. The crater is 1.2 kilometers (0.74 miles) in diameter and 200 meters deep. It formed approximately 49,000 years ago when an iron meteorite that was roughly the size of a school bus struck the Arizona desert east of what is now Flagstaff. Wednesday, March 3, 2010 11
  • 12. The Earth: Arizona Impact In a blinding flash, a huge iron-nickel meteorite or dense cluster of meteorites, estimated to have been about 150 feet across and weighing several hundred thousand tons, struck the rocky plain with an explosive force greater than twenty million tons of TNT (or around 1000 Hiroshima bombs). Traveling at supersonic speed, this impact generated immensely powerful shock waves in the meteorite, the rock and the surrounding atmosphere. In the air, shock waves swept across the level plain devastating all in the meteor's path for a radius of several miles. Wednesday, March 3, 2010 12
  • 13. Tunguska Blast Trees near the Podkamennaya Tunguska River in Siberia still looked devastated nearly two decades after a large meteorite exploded above the ground in June 1908. The Tunguska event, which ranks as one of the most violent cosmic impacts of this century, leveled nearly 800 square miles of forested taiga. Smithsonian Institution Wednesday, March 3, 2010 13
  • 14. The Earth: Chicxulub 2:25 Chicxulub impact visualization The Chicxulub Crater is believed to be the result of the collision with an asteroid measuring some 10 to 20 km across. The environmental effects that accompanied its formation were thought to have been responsible for the mass extinction at the end of the Cretaceous period, about 65 million years ago, in which the last of the dinosaurs, along with many other species, disappeared (see Cretaceous-Tertiary Boundary). Wednesday, March 3, 2010 14
  • 15. Ice Ages Milankovich cycles are cycles in the Earth's orbit that influence the amount of solar radiation striking different parts of the Earth at different times of year. They are named after a Serbian mathematician, Milutin Milankovitch, who explained how these orbital cycles cause the advance and retreat of the polar ice caps. Although they are named after Milankovitch, he was not the first to link orbital cycles to climate. Adhemar (1842) and Croll (1875) were two of the earliest. Wednesday, March 3, 2010 15
  • 16. Ice Ages Wednesday, March 3, 2010 16
  • 17. Earth: Life? Wednesday, March 3, 2010 17
  • 18. Earth’s Geology LACC: §7.2, 3, 4 • Understand Earth’s interior: core (iron; solid inner, liquid outer), mantle (rocky), crust; differentiation • Understand Earth’s geological features: a few hundred million years old; plate tectonics and erosion (and a few hundred impact craters) • Understand Earth’s some of the Earth’s extinction events: impacts (e.g. Chicxulub), Milankovich cycles An attempt to answer the “big question”: what is out there? Wednesday, March 3, 2010 18
  • 19. LACC HW: Franknoi, Morrison, and Wolff, Voyages Through the Universe, 3rd ed. • Ch. 7, pp. 171-172: #1. Due at the beginning of next class period. Be thinking about the Solar System Project. Wednesday, March 3, 2010 19
  • 20. Earth’s Atmosphere LACC §7.2, 3, 4 • Earth’s Atmosphere: composition, pressure, and temperature • The Evolution of Earth’s Atmosphere • Life on Earth An attempt to answer the “big question”: where did we come from? Wednesday, March 3, 2010 20
  • 21. The Earth: The Atmosphere • The greenhouse effect on Earth heats our planet by about 55°F. • The Earth’s atmosphere (and magnetosphere) protect us from dangerous radiation and meteors. • Earth’s surface temperature and pressure allow for liquid water on its surface! Wednesday, March 3, 2010 21
  • 22. The Earth: The Atmosphere Composition 1 bar surface pressure • N2 77% • O2 21% 59°F average • Ar 1% surface • H2O varies temperature • CO2 varies Wednesday, March 3, 2010 22
  • 23. Earth: Black Body Temperature ....Earth ... 255 K (-18 °C or -0.5 °F). ...this would be the temperature of the planet if it had no atmosphere. Wednesday, March 3, 2010 23
  • 24. Earth: The Greenhouse Effect Wednesday, March 3, 2010 24
  • 25. Earth: The Greenhouse Effect [The] graphic [on the previous slide] explains how solar energy is absorbed by the earth's surface, causing the earth to warm and to emit infrared radiation. The greenhouse gases then trap the infrared radiation, thus warming the atmosphere. Wednesday, March 3, 2010 25
  • 26. Earth: The Greenhouse Effect The main greenhouse gases Greenhouse gases Chemical Pre-industrial Concentration Atmospheric Anthropogenic Global warming formula concentration in 1994 lifetime (years)*** sources potential (GWP) * Fossil fuel combustion Carbon-dioxide CO2 280 ppmv 358 ppmv 50-200 Land use conversion 1 Cement production Fossil fuels Rice paddies Methane CH4 700 ppbv 1720 ppmv 12-17 Waste dumps 21 ** Livestock Fertilizer Nitrous oxide N 2O 275 ppbv 312 ppmv 120-150 industrial processes 310 combustion Liquid coolants. CFCs CFC12 0 503 pptv 102 Foams 125-152 HCFCs HCFC-22 0 105 pptv 13 Liquid coolants 125 Production Perfluorocarbon CF4 0 110 pptv 50 000 of aluminium 6 500 Production Sulphur hexa-fluoride SF6 0 72 pptv 1 000 of magnesium 23 900 Note : pptv= 1 part per trillion by volume; ppbv= 1 part per billion by volume, ppmv= 1 part per million by volume * GWP for 100 year time horizon. ** Includes indirect effects of tropospheric ozone production and stratospheric water vapour production. *** On page 15 of the IPCC SAR. No single lifetime for CO2 can be defined because of the different rates of uptake by different sink processes. GR I D Arendal UNEP water? Source: IPCC radiative forcing report ; Climate change 1995, The science of climate change, contribution of working groupe 1 to the second assessment report of the intergovernmental panel on climate change, UNEP and WMO, Cambridge press university, 1996. Wednesday, March 3, 2010 26
  • 27. Earth: Atmospheric Evolution Wednesday, March 3, 2010 27
  • 28. Earth: Atmospheric Evolution Materials for the atmosphere were brought to the earth by comets accreted during its formation, then released by volcanoes (From Don Dixon index.html). Additional late- arriving comets would have added additional material to the oceans and atmosphere. Wednesday, March 3, 2010 28
  • 29. Earth: Atmospheric Evolution Origin of the Earth's Atmosphere After losing most of its original H and He, the Primordial Atmosphere of the Earth was built up by outgassing of the crust by volcanos: • Mostly H2O and CO2 • Small amounts of N2 and sulfates • No oxygen (O2). This is very different than our present atmosphere. How did our atmosphere get the way it did? Wednesday, March 3, 2010 29
  • 30. Earth: Atmospheric Evolution Wednesday, March 3, 2010 30
  • 31. Earth: Atmospheric Evolution Wednesday, March 3, 2010 31
  • 32. Earth: Atmospheric Evolution Where did all the CO2 go? The primordial atmosphere had ~1000 times more CO2 than it does now. Where did it all go? • H2O condensed to form the oceans. • CO2 dissolved into the oceans and precipitated out as carbonates (e.g., limestone). Most of the present-day CO2 is locked up in crustal rocks and dissolved in the oceans. By contrast, N2 is chemically inactive • It stayed a gas in the atmosphere and become its dominant constituent. Wednesday, March 3, 2010 32
  • 33. Earth: Atmospheric Evolution Where did the O2 come from? The second major constituent of the present-day atmosphere is Oxygen (O2), but it was absent in the Primordial Atmosphere. Where did all the O2 come from? • Molecular Oxygen (O2) comes primarily from photosynthesis in plants and algae. • The O2 content of the atmosphere has increased from 1% to 21% during the past 600 Myr. Ozone (O3): • Forms in stratosphere from O2 interacting with solar UV photons. • Blocks UV photons from reaching the ground. This made land life possible as solar UV radiation is hazardous to life. The presence of O2 and O3 in our atmosphere is a sign of life (photosynthesis). Wednesday, March 3, 2010 33
  • 34. Earth: Life? • 3.9 billion years ago: chemical evidence of life • 3.5 billion years ago: Stromatolite colonies • 2 billion years ago: O2 accumulate is the atmosphere • 65 million years ago: Chicxulub impact results in extinction of dinosaurs • 200 thousand years ago: modern humans • 1 hundred years ago: radio broadcasts Wednesday, March 3, 2010 34
  • 35. Earth: Life? Colonies of trillions of these bacteria built up cabbage-like structures called stromatolites. The bulk of a stromatolite colony consists of layers of calcium carbonate interspersed with mattes deposited by the cyanobacteria (which are photosynthetic). Stromatolites still exist on Earth but are rare (mainly at two localities in Australia). Wednesday, March 3, 2010 35
  • 36. Earth: Climate Change Wednesday, March 3, 2010 36
  • 37. Earth: Climate Change The Medieval Warm Period was a time of warm climate in Europe, the height of which was from about 950 until 1100 A.D. The warm climate overlaps with a time of high solar activity called the Medieval Maximum. The Medieval Warm Period occurred before the Little Ice Age (1350-1850 A.D.), a time of particularly cool climate in Europe and other places around the world. The graph on the left, a reconstruction of average global temperatures over the past 1000 years, shows that during the Medieval Warm Period the temperatures were likely similar to the first part of the 20th century, climate cooled during the Little Ice Age, and has warmed dramatically in recent decades. Temperatures during the Medieval Warm Period were likely cooler than the temperature has been for the past few decades. Wednesday, March 3, 2010 37
  • 38. Earth: Climate Change All five global temperature estimates presently show stagnation, at least since 2002. There has been no increase in global air temperature since 1998, which was affected by the oceanographic El Niño event. This does not exclude the possibility that global temperatures will begin to increase again later. On the other hand, it also remain a possibility that Earth just now is passing a temperature peak, and that global temperatures will begin to decrease within the coming 5-10 years. Only time will show which of these possibilities is the correct. %20global%20temperature%20estimates Wednesday, March 3, 2010 38
  • 39. Earth’s Atmosphere LACC §7.2, 3, 4 • Earth’s Atmosphere: composition (N2, O2), pressure (1 bar), and temperature (59 °F), the greenhouse effect • The Evolution of Earth’s Atmosphere: volcanic outgassing, comet impacts, thermal escape. • Life on Earth: earliest fossils, O2 levels, climate change An attempt to answer the “big question”: where did we come from? Wednesday, March 3, 2010 39
  • 40. LACC HW: Franknoi, Morrison, and Wolff, Voyages Through the Universe, 3rd ed. • Ch. 7, pp. 171-172: #5. • Ch 8: Tutorial Quizzes accessible from: http:// fid=M20b&product_isbn_issn=9780495017899&discipline_number=19 Due at the beginning of the next class period. Be thinking about the Solar System Project. Wednesday, March 3, 2010 40