EAR101-M001 class notes
EAR101-M001 class notes EAR 105 - M001
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This 11 page Class Notes was uploaded by Cara-Liesel Ransom on Sunday September 18, 2016. The Class Notes belongs to EAR 105 - M001 at Syracuse University taught by C. Junium in Fall 2016. Since its upload, it has received 119 views.
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Date Created: 09/18/16
Cosmology and the Birth of Earth The Universe contains two basic elements: 1. Matter 2. Energy (the two are related by theory of special relativity) The scientific method provides a foundation to explore the cosmos. 1. The Sun, Earth, and other celestial objects. People didn’t really get what was going on, so they tried to take measurements. Over time they got better at it. Early astronomers: looked and guessed, some make measurements. 1. The stars are fixed relative to each other. a. All the stars rotate about a fixed point. 2. The planets move against the background of stars. (OBSERVATIONS) Not obvious that Earth is a planet. Not obvious that the Sun is a star. The earliest observers had no idea what was going on, but they tried. The planets follow a different pattern: asteres planeti. The Babylonians. The Earth was the center of the universe. Two competing views of the Universe. 1. The Universe is geocentric. a. Heavenly bodies circle around a motionless central Earth. b. The idea held as a religious dogma for 1,400 years. 2. The Universe is heliocentric. a. Sun-centered universe b. Idea was unpopular until the renaissance The Copernican Revolution: modern science Renaissance: a new age of discovery in 1400’s Europe. It spawned a new age of scientific exploration. 1. Birth of empirical study 2. They TESTED, rather than working to PROVE an idea. 3. It got them in trouble. a. Copernicus b. Kepler c. Brahe d. Galileo e. Newton Observations led to advancements Telescopes allow astronomers to better see the Universe. 1. Star: immense sphere of incandescent gas 2. Galaxy: groups of stars a. 100 billion galaxies constitute the visible universe. 3. Milky Way Galaxy: the galaxy that contains Earth. a. There are over 300 bullion other stars in the Milky Way. b. The Solar System is on the outer edge of the Milky Way. Our Solar System Objects in the Solar System 1. The Sun: contains 99.8% of all the mass in Solar System 2. Small objects 3. Planets (we are the dregs of the aftermath of the creation of the Sun) a. Orbit a Star (the Sun) b. Roughly spherical shape. The Nature of Our Solar System Two groups of planets: 1. Terrestrial planets a. Small, dense, rocky planets b. Mercury, Venus, Earth and Mars 2. Gas-giant planets a. Large, low-density planets b. Jupiter, Saturn, Uranus, and Neptune Planets are ubiquitous in the Universe Exoplanets 1. Planets found outside our Solar System a. Kepler Space Telescope b. 2,000 exoplanet candidates found c. Milky Way may contain 14 billion Earth-sized exoplanets Exoplanets confirm the “Nebular Theory” Detailed measurements yield good data and ~correct answers. Eratosthenes calculated the circumference of Earth in ~200 B.C. He measured shadows in deep wells 800 km apart. 1. Measurements were taken at noon on the same day. 2. Syene- shadow absent (directly overhead) 3. Alexandria – shadow at 7.2^0 He calculated the Earth’s circumference as 39,300 km. He was correct! The Earth is 40,008 km right now. Earth’s position in the galaxy. Earth spins on an axis of rotation. 1. Axis tilt of 23.4 degrees. 2. Rotational velocity is 1,674 km/hr at the equator. Earth orbits the Sun 1. 159 million km elliptical path 2. Orbital velocity is 108,00 km/hr. Solar System revolves around the center of the Milky Way. 1. One revolution per 250 million years. 2. Solar system velocity is 720,000 km/hr. ~The Big Bang and Nebular Theory~ The Big Bang. Explodes. In the next 10^-32 seconds. IN 1 microsecond proton formed .001 seconds 3 minutes fusion ends, it requires dense collection of mass under great pressure that ends. 380,000 years. The cosmic Microwave Background. When this happens, protons join with electrons: essentially the beginning of light. Over time, destruction and creation of stars The Cosmic Microwave Background: it confirmed the Big Bang. Birth of the First Stars After continued expanision, atoms and molecules accumulated into patchy clouds. 1. Called nebulae Gravity caused the collapse of gaseous nebulae. Collapse resulted in increases in: 1. Temp. 2. Density. 3. Rate of rotation Stars take one of two paths after formation. It can burn up all of it’s fuel and kind of shrink up. It won’t glow very bright. OR. It can expand and grow as the star matures, the fusion shuts off or explodes. It becomes a super nova. “We are all made of stars. But so is everything else.” Nucleosynthesis forms elements. Big Bang nucleosynthesis formed the lightest elements. 1. H, He, Li, Be, and B 2. All have atomic numbers less than five. Heavier elements are from stellar nucleosynthesis and supernovae. (Ne, C, Su, K, Mg, Cu) Nucleosynthesis control the abundance of elemnts in our solar system (note log scale) ~Formations~ The Supernova collapses into a new star and proto-planetary disk. Earth accretes from protoplanetary disk ~4.6 billion years ago. Formation of the Earth is dated at 4.55 billion years. Oldest materials on Earth are 4.4 billion years. Higher mass matter stays close to the star (like Earth) Nebular Theory for Forming the Solar System The ball at the center grows dense and hot. Fusion reactions begin; the Sun is born. Dust in the rings condenses into particles. Particles coalesce to from planetesimals. EAR101 Monday 9/12: Earth’s Layers: a summary Earth has a layered interior. o Crust Continental Oceanic o Mantle Upper Transitional Lower o Core Outer- liquid Inner – solid These layers are subdivided on the basis of seismic waves. It gets hot and the pressure increases Change with depth o Pressure (P) of overlying rock o Temperature (T) increases from heat generated deep within Earth’s interior Geothermal gradient o The rate of T changes with depth o The geothermal gradient varies How do we know about the Earth’s interior? Density o A plumb bob is deflected by a nearby mountain mass. o Degree of deflection can be used to calculate Earth’s mass. o The density from this method (4.5 g/cm^3) is much higher than the density of the thin outer crust (2.5 g/cm^3). o This suggests that density must increase with depth. o Essentially, the density of the Earth must be significantly bigger than the density of the surface. Early Clues to Characterize the Interior The first key to understanding Earth’s interior density o IN 1896, Emil Wiechert made important contributions. He determined that metal must be present in Earth’s interior. He deduced that there is metal in Earth’s core. Earthquakes ultimately proved what we now know about the Earth’s interior Seismic wave velocities change with density. o We can determine the depth of seismic velocity changes. o Hence, we can tell where densities change in the Earth’s interior. What is the composition of the layers? Studied meteorites as analogs for core and mantle. Conducted lab experiments. o Rocks from the mantle are occasionally found at the Earth’s surface o Only certain minerals are stable under high Pressure and Temperature. The Crust: we can sample the crust easily Thin, outermost “skin” of Earth. o Thickness varies from 7-70 km Continental crust is thicker than the oceanic crust. Oceanic crust is more dense than the continental crust. The base of the crust is called the Moho. o Area where seismic velocity changes o Separates crust from upper mantle The Lithospehere: important for plate tectonics We can also regard layering based on rock strength. o Lithosphere – the crust and uppermost mantle Rigid/brittle (breaks rather than bends) Broken into tectonic plates o Asthenosphere – upper mantle below the lithosphere (super manageable) The Mantle Solid rock (NOT magma) Largest Earth Later o 2,885 km thick o 82% if Earth’s volume. It is essentially one, composition rock. o Upper mantle is primarily peridotite Two sublayers o Upper mantle (Moho to 660 km) o Lower mantle (660 – 2890 km) Undergoes slow convection o Hot rocks rise, cold rocks sink The Core An iron-rich sphere with a radius of 3,471 km Seismic waves segregate two radically different parts o The outer core is liquid; inner core solid o Outer core Liquid iron-nickel-sulfur 2,255 km thick Density is 10-12 g/cm^3 Crust: continental and oceanic Mantle: solid rock, warmer as you go deeper. Core: liquid inner core, solid outer core. We know these things based on seismic waves Continental Drift and an Introduction to Plate Tectonics Alfred Wegener o German meteorologist and polar explorer o Wrote “The Origins of Oceans and Continents” in 1915 He suggested land masses slowly ove (continental drift) He hypothesized a former supercontinent, Pangaea. 1. The Fit of the Continents. a. The continents seemed to fit together like a puzzle b. The fit couldn’t be coincidental c. Shorelines made a rough fit. d. Simply not enough 2. Evidence of past glaciation in warm areas a. Evidence of past glaciers found on four continents, not at the poles 3. Locations of Past Glaciations a. On a map of Pangea, glacial deposits converge. b. A former south pole, perhaps. 4. Climatic belts connect across continents a. Evidence for warm conditions connected up, deserts and such. 5. Mountain belts connect across the Atlantic. a. Appalachian Mountains have matching ranges in Africa and through Europe. However, though Wegener was correct he really couldn’t explain how the continents moved. So: 1. Proposed that the Earth’s spin caused the continents to plow through the ocean floor. 2. This hypothesis was highly criticized. 3. Without any evidence and tests, his idea faded until the ocean floor began to become more widely mapped. Wednesday 9/14 ~Interlude~ Marie Tharp: innovator in the study of the sea floor and plate tectonics. Tharp used depth data from scientific cruses to map the sea floor ( she was not allowed on the ships.) The “Tharp Map” documented the longest continuous feature on Earth (mid-ocean ridge) and formed the basis for initial theories on plate tectonics. It really started to take off when people noticed earth quakes started taking place over and over at these points, these plates. Mapping of the sea floor was done in concert with a wide array of sensors, one of which was a magnetometer. “Magnetic anomalies” were seen on the seafloor. ~The variability in Earth’s magnetic field is recorded in the lava rocks on the seafloor. ~The same magnetic signatures can be used to determine the latitude of landmasses in the past. It is called paleo magnetics and it proves paleo latitude. It allows us the trace the ‘apparent wander of continents in the past. ~recognizing this helps us know where plates were in the past as well as acknowledging continental drift. ~There still was not an appropriate mechanism that unified continental drift. ~The age of crust increases from the mid-ocean ridge at the middle to the edges of the ocean basin. ~The amount of heat correlates with the age of the sea floor. Younger = more heat ~The Theory of Plate Tectonics Sea-floor spreading. o Upwelling mantle erupts at the mid-ocean ridges o New crust moves away from ridges, gathering sediment o At traces, the sea-floor sub ducts back into the mantle Provides a mechanism for continental drift o Sea-floor spreading o Sea-floor subductions ~Two types of plates and three types of boundaries Lithosphere is fragmented into ~20 tectonic plates Plates move continuously at a rate of 1-15cm/yr. o Slow on a human time scale; extremely rapid geologically. Plates interact along their boundaries ~Plate Boundaries: Three Types Divergent boundary – tectonic plates move apart. o Lithosphere thicks away from the ridge axis o Also called: spreading boundary, mid-ocean ridge, ridge Convergent boundary – tectonic plates move together o The process of plate consumption is called subduction. o Also called: convergent margin, subduction zone, trench Transform boundary – tectonic plates slide sideways o Plate material is neither created nor destroyed. Also called, transform fault, transform
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