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Geology 101


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How did the universe form? What evidence do we have for this model?
All matter was condensed into a single point, which was unstable and led to an explosion (big bang). Evidence: Doppler shift (approaching - high freq.) Also, Penzias and Wilson radio data - left over radiation.
How did the solar system form?
There was a cloud of dust formed in the big band, and other stars. Cloud collapses under own gravity. Rotation+collapse=flattening into protoplanetary disk. The gas is densest at the center of the dirk, and a star is formed. Particles in the disk collide
How did the moon form? Evidence?
A mars-sized protoplanet crashed into earth, debris formed a ring around earth which accreted to become the moon. Evidence: Earth and moon --> same elemental composition
how did earth aquire its stratified (layered) internal structure?
Heavy elements (iron, nickel, some sulfur) sink. Light elements (silicon, oxygen, aluminum)(less dense) rise. This is called differentiation.
What are the 2 categories of planets in the solar system? How and why are they different?
TERRESTRIAL PLANETS: close to sun, (gas) iron is blown away by solar winds.(Mercury, venus, earth, mars.) Earth like, because they constist of a shell of rock surrounding a core of iron alloy, like earth does. JOVIAN/GAS GIANTS:(Jupiter-like) Jupiter, Saturn, Uranus, and Neptune. Large mass. Gas balls. Far from sun - liquid/solid iron can\'t be blown away by solar winds.
Mass distribution in solar system
98% = Sun, 1.5% = Jupiter, .05% = Everything else.
What is earth made of? How do we know this?
Crust (light silicate rocks), Mantle (dense silicate rocks), Core (Iron and some nickel). We know this because of the similar elements in meteorites, and how seismic waves travel thru the earth.
How is Earth divided by rheology? How do we know this?
Lithosphere: Solid, rigid layer. Asthenosphere: Plastic region. Mesosphere: Lower mantle, soild. Outer Core: Liquid. Inner core: soild. We know because of seismic waves.
Why does Earth have a magnetic field?
There is iron in the core that is solid inside and liquid outside. This, and the spinning electric current, generate a magnetic field.
On average, how often does the earth switch polarities?
Every 200,000 years.
How old is Earth?
4.5 Billion Years old.
What methods have been used to estimate age of the earth? Ussher, Kelvin, Henri
Ussher: Bible and generations. Included catastrophism. est. 6000 yo. Opposite view: uniformitarianism, which is the idea that processes we see today were the same back then. Lord Kelvin: Cooling rates. Est. 20-40 million yo. Henri discovered radioactivity, realized earth much older than that because kelvin\' model didn\'t include added heat.
What is an isotope? What causes radioactivity?
When the number of neutrons changes, it becomes and isotope. the nucleus of an unstable atom splits apart to form a new atom. An atom may undergo multiple decays before it is stable.
A half life is...
How long it takes for half of the isotopes to decay. Shorter half-life = more unstable.
so, after 1...2...3...4 half lives...
1: 50% p 50% d 2: 25% p 75% d 3: 12.5% p 87.5% d 4. 6.25% p 93.25% d
what determines whether or not a rock can be dated radiometrically?
Parent-daughter present, has the right isotopes, if its the right age (to young = not enough daughters, too old - not enough parents.)
How do you date a rock?
measure amt of parent and daughter isotopes. Find age by looking at ratio of parent to daughter.
How is the geologic time scale divided? Why do the divisions occur where they do?
Pre-cambrian (no life), Paleozoic (first life), Mesozoic (dinos), Cenozoic (mostly mammals)
how much of earth\'s history has included life?
13%, 550 million years?
Eras: Precambrian, Paleozoic, Mesozoic, Cenozoic, Holocene.
Precambrian: Formation of planet - first life. 87% earth\'s history. Paleozoic: 544-250ma. First life. Pangea. Mass extinction. Mesozoic: 250-65ma. Dinos. Reptile dominant, warm climate, mass extinction. Cenozoic: 65ma-present. Mammals dominant. Quaternary period. Holocene - last 10,000 years.
History in a year: When did dinos live? how long have humans been around? when did fossils become prevelant?
dinos: died dec 26. humans: last hour fossils: December
Continental drift theory -> evidence, problems
Alfred Wegener. Continents move in time over the surface of the earth, and were once grouped together in pangea. Explains fit of continents, rock assemblages, fossil dist., glaciated regions, mag. pole location = consistent. Problems: No model for how or why continents move, not reasonable for continents to plow thru ocean crust and mantle. Langauge barriers, WWI, outside area of expertise, revolutionary.
Plate tectonics -> evidence, problems
Harry Hess - sea floor spreading. Evidence: Low sediment thickness on (young) mid-ocean ridges. Magma rises in fracture and forms new rock -->high hear flow (active volcanism). Old oceanic crust goes into trenches. Age of seafloor confirms.
what are the differences between CD and PT?
CD: Only continents move Continents plow thru solid earth No viable driving mechanism. PT: Plates of oceanic and continental crust (entire surface) moves. Plates float on asthenosphere. Convincing driving mechanism.
Story behind plate tectonics revolution, when?
1912-Wegener proposes CD New seafloor data Hess comes up with seafloor spreading idea, timid. 1960s? In 1963, Vine and matthews observe magnetic lineations off the coast of PNW. This confirms sea floor spreading, age of rocks close and far from ridge.
What do hot spot volcanoes tell us about plate velocity?
Plates move very slowly, cm/yr.
What are the driving forces of plate tectonics?
Convection --> minor Ridge push -> moderate slab pull -> strong force

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