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146 Cards in this Set
- Front
- Back
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What do you do with a seismograph?
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It records a plot of bedrock motions (plot of the oscillations of the suspended weight = seismogram).
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What can the scientists determine with seismograms? (3)
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1. location of earthquakes and similar disturbances
2. intensity of earthquake 3. basic properties of the underlying material that makes up the solid Earth |
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Name the zones of Earth's interior. (3)
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1. crust
2. mantle 3. core (has inner (solid) and outer (liquid) core) |
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How do scientists determine that there is a liquid-outer and solid-inner core from seismographs? (2)
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1. seismologists deduced that the outer part of the core must be molten bc certain types of seismic waves that do not travel through liquid are observed to not propagate through the core
2. Earth has magnetic field |
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Explain the observation of density and seismic wave changes.
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As the density of the medium increases, the refraction of the seismic waves changes.
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Explain the property of s-waves and p-waves.
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s-waves cannot propagate through the liquid outer core, and therefore there is a large shadow zone where they do not arrive. p-waves propagate through liquid outer core, and therefore there the compressional waves are bent extremely at the core-mantle boundary, creating a partial shadow zone for p-waves in the southern hemisphere.
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How is density of Earth found?
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By observing how seismic wave velocities vary as a function of depth.
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How is composition of the mantle found?
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By observing the composition of the volcanic material.
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How is composition of the core (Fe, Ni) found?
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By observing the need to rationalize the Earth's density.
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Why does Earth need iron core?
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Because Earth is denser than the crust which is composed of silicate minerals. So it needs denser material found in meteorites which is iron and the only place to put Fe is in the core for icon/molten core is consistent with presence of magnetic field.
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Are there regions where liquid/solid interfaces exist? When?
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Yes. As depth increases, it goes from below melting point (mantle: 0-2700 km) to above melting point (molten outer core: 2700 km-5200km) to below melting point (solid inner core: 5200km - 6500km) again.
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What are the two accretion theories of Earth formation?
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1. layered accretion model (heterogeneous accretion model): earth accreted/formed as layers (first Fe, the silicates, etc.). Not believed to be viable/workable.
2. homogeneous accretion model: earth was formed from bombardment and accretion of chondritic meteorites. |
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How did the Earth come to have its present interior structure? Explain.
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Through differentiation, process of gravitational separation according to density. And it leads to the development of differences in internal composition. So the Earth was melted by heat arising from gravitational energy left from the formation of the planet, meteor bombardment and decay of radioactive material trapped in the body of the Earth. While the Earth was molten, gravity concentrated denser material near the center and less dense material nearer the surface. When the Earth solidified again (except for the liquid outer core) it was left with a layered structure with more dense material like Fe and Ni near the center and less dense rocks nearer the surface. As the outer layers cooled and solidified, large cracks developed bc of thermal stress, leaving the lithosphere broken up into large blocks or (tectonic) plates.
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Explain the chemical separation during differentiation.
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The separation of Fe from silicates by means of differentiation left behind O as a volatile element available to form H2O (oceans), CO2 (photosynthesis) and O2 (respiration). It had a major impact on Earth's habitability.
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When did differentiation occur?
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Soon after formation/birth of the solar system.
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Define minerals and rocks.
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A mineral is naturally occurring inorganic element or compound, with a definite internal arrangement of ions (as in a solid) and a chemical composition that is fixed or varied within narrow limits. Mineral is composed of single substance.
Rocks are mineral aggregates made up of several different minerals (compounds or elements). |
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Which element is most prevalent by mass in Earth's crust? What is unique about it?
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Oxygen. It is extremely volatile by itself hence it only appears in combination with other elements as oxides (for ex. silicates).
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What are the 2 categories of rocks in terms of their mineral content?
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ferromagnesian and non-ferromagnesian silicates
(ferro=latin word for iron) |
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What are the 3 broad categories based on how rocks were formed? (explain them all thoroughly and give examples for each)
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1. igneous rock - formed from crystallization of magma
(a)extrusive/volcanic igneous rock - rapid cooling; usually derived from upper mantle and so relatively rich in Fe and Mg (which is mafic = balsatic (olivine, pyroxene, plagioclase)) (b)intrusive/plutonic igneous rock - slowly cooling; usually derived from crust and so relatively rich in silicates and Al (which is sialic = granitic (fieldspar, quartz, mica)) 2. sedimentary rock - formed by sedimentation and compaction of material (lithification); tends to form in layers -Detrital (shale, sandstone - both from mud) -Biological (limestone - from shells and coral, chert - from diatoms) -Evaporites (gypsum) - CaSO(small4)2(H(small2)O), anhydrite - CaSO(small4), halite - NaCl, calcite - CaCO(small3) 3. metamorphic rock - chemically altered while in the solid state from exposure to high temperatures and pressures (re-crystallization) -slate (derived from shale - clay, chlorite, mica, quartz) -marble (derived from limestone - calcite) -gneiss (derived from slate or granite - mica, quartz, amphibole, feldspar) |
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Define magma and lava.
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Magma is molten or partially molden rock beneath the Earth's surface.
Lava is when magma erupts onto the surface. |
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Which rock is the best to learn about the process that lead to the generation of crust? Why?
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Igneous rock since crustal material is generated from the mantle.
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Explain 3 igneous rock properties.
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1.grain size (fine/aphanitic vs. coarse/phaneritic)
2.where formed (extrusive/volcanic vs. intrusive/plutonic) Volcanic is formed when magma in earth's interior rises to the surface through pipes or fractures in the crust. most readily recognized representation of igneous rocks. Plutonic is formed when magma cools within the earth. They form plutons/intrusions which remain hidden from sight until erosion removes the overlying rocks. 3.composition (mafic vs. felsic) mafic =less silicon=more iron=denser (dark in color, have relatively high specific gravities >3.0, flow relatively easy) felsic=more silicon=less iron (light in color, have specific gravities < 3.0, viscous/thick fluid, do not flow as readily as magic magma |
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Explain properties and characteristics of oceanic crust (crust depth, age, density, rock type)
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crust depth: shallow, 5-12 km
age: young rocks, less than 200 mil years old density: 3.0 x 10^3 kg m^-3 rock type: mainly basalt |
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Explain properties and characteristics of continental crust (crust depth, age, density, rock type)
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crust depth: deeper, average 40km, 75km beneath young mountain range
age: older, generally over 1500 mil years density: 2.6 x 10^3 kg m^-3 rock type: range of granites with thin covering of sedimentary rocks |
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What are the 2 major rock-players in crust? What are they enriched with?
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Basalt (ocean) which is enriched with Al and Ca and granite (continent) which is enriched with Na and K.
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What does the increase in ion size do?
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It lowers the melting temperature and makes the ions more readily be "kicked-out" of mineral/rock via partial melting.
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Explain Wegener's Continental Drift Theory.
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Theorized by Alfred Wegener in 1902, he pieced together evidence from a broad range of the earth sciences to hypothesize that all of the present-day continents were once part of Pangaea (single supercontinent). He hypothesized that 200-300 mil years ago Pangaea split and its pieces have been moving away from each other ever since.
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Name 5 evidences upon which Wegener built his hypothesis.
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1. close fit between the coastlines of Africa and South America when using continental shelf edges (that is shoreline has been deformed by erosion)
2. glacial features from essentially the same time period appear in South America, Africa, India and Australia. 3. fossils of identical plants and animals found on all continents. Suggested that land bridges, now sunken, had once connected the continents. 4. large-scale geological features on different continents matched with the continents were brought together. (Appalachian mtns in NA and Scottish Highlands; distinctive rock strata of Karroo system in South Africa and those of Santa Catarina in Brazil.) 5. fossils found in some places do not match the current climates. (glossopteri, Australian dinosaur fossils in Dinosaur Cove; fossils of tropical plants (ferns and cycads) found on the Arctic island of Spitsbergen.) |
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How did Wegener construct Pangea?
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By using the location of specific rock types to determine the distribution of climate zones in the geologic past. (glacials from tills and striations=polar; sand dunes=deserts; coral reefs=tropics)
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What are the 2 explanations of resulting distribution of Pangea?
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1. poles have wandered
2. continents have drifted |
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What were the problems with Wegener's Continental Drift Theory? (3)
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-lack of viable physical mechanisms for the "drifting continents" (Wegener proposed that Earth's spin and tidal forces caused the continents to move but not possible).
-hypothesis is footloose -continents would be deformed by motion through ocean crust if this was real |
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Explain 1928 study of plate tectonics.
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Arthur Holmes proposed that convection currents (which bring hot magma/rock up from the deep mantle and cooler rock downward) could drive continental motion.
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Explain 1940's study of plate tectonics.
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Mapping of seafloor during the WWII revealed complicated chain of subsea volcanic mountains along the center of ocean basins forming a system of mid-ocean ridges.
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Explain 1950's study of plate tectonics.
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Seismologists showed that the mid-ocean ridges were also an active seismic belt/zone of earthquakes. It was proposed that the seismic belt corresponded to a trough/rift system running down the center of the ridges.
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Explain 1968 Deep Sea Drilling Project.
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It revealed that ocean floor is geologically young (180 mil years old) and ocean floor age has a specific pattern with youngest rocks near central ridges and increasing ages away from ridge axis.
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Explain 1962 H.H. Hess (and Dietz) independently developed theory of sea-floor spreading.
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Given age variation of seafloor and the fact that ocean floor is basaltic and differs from granitic continental rocks, it was proposed that:
-magma comes to ocean floor at ridges -magma erupts as sub-sea volcanoes and produces new basaltic crust which slowly spreads causing the ocean floor to move away from the central ridges; when the ocean floor reaches the continent it plunges down below the continent because granitic material is not as dense as basaltic material. And new mountains form along boundaries. |
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Where did the support for sea-floor spreading theory come from?
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It came from a study of the magnetic polarity (which pole is north and which is south) of the basaltic material of the seafloor. Magnetic orientation of igneous rock tells us that polarity of earth's magnetic field at the time the rock was formed because as lava cools and form rocks, the material becomes magnetized in the direction of the earth's magnetic pole at that time and remains that way.
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What did Vine and Matthews explain about the pattern of magnetic anomalies?
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In 1963, they proposed that lava erupted at different times along the rift at the crest of the mid-ocean ridges and preserved the record of magnetic anomalies. Creation of the observed pattern requires sea-floor spreading. (if north magnetic pole is in the northern hemisphere, magma solidifies along the edge of the oceanic plate it preserves a magnetic record of the Earth's magnetic field at that time. new crust with normal magnetic pattern; if magnetic pole is in the southern hemisphere, the rocks record a reserve magnetic pattern.)
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Explain 1968 Theory of Plates by Dietz, McKenzie and Parker.
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They combined sea-floor spreading and continental drift. As they found out that Earth's outer shell - the lithosphere - consist of rigid plates, the plates slide on the softer asthenosphere as the plates move they carry continents and ocean floor and when continents and ocean floor converge, a deep valley is formed and ocean floor 'subducts' beneath continent.
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Explain oceanic vs. continental crust and isostacy.
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-oceanic crust is composted of basalt with density of 2.9 g/cm^3; relatively thin (5km)
-continental crust is composed of granite with density of 2.7 g/cm^3; relatively thick (25-50km) -granite is less dense than basalt so continental crust tends to "float" above oceanic crust. continental crust is thickest beneath high mtn ranges and thinnest beneath lowlands. -isostatic equilibrium allows lithosphere to be supported by asthenosphere -the amt of asthenosphere displaced is equal to mass of overlying lithosphere -thick continental crust must have deep "root" below to support its weight. some areas of continental lithosphere are not isostatic equilibrium bc the mass in that area has recently and abruptly changed. -as continents erode, base of granitic crust rises (like stone mtn's outcropping) to maintain isostatic equilibrium |
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Why is continental crust granite?
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When oceanic plate (that is wet basaltic material) is subducted/one plate move under another plate, it is heated to moderately high temperatures that lead to the formation of felsic magmas. These felsic magma crystallizes into granitic, and usually intrusive rock, thus forming the bedrock for continental crust.
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What is the conclusion of Plate Tectonic Theory and Wegener's Theory of Continental Drift?
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Continents do not plow through oceanic crust; instead continents and oceanic crust are considered to be part of plates that move on the plastic asthenosphere. A driving force, convection currents, moves the plates.
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What does the plate tectonics provide? (2)
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-engine that drives the rock cycle and maintains the habitable planet by recycling nutrients on ~100 million year time scale
-framework for understanding topographic feature of the planet, volcanic and seismic activity. |
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How many moons and planets are in our solar system?
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33 moons and 9 planets
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Which planets do the moons not orbit?
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Mercury and Venus
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Describe two types of moons.
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1. chondritic with densities of ~3
2. solar/outer planet like with densities of ~1.2 |
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Why are there rings in some cases and moons in others?
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Because of tidal forces and Roche limit.
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What is Roche Limit?
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It is the orbital distance at which a satellite with no tensile strength for example Liquid Satellite will begin to be tidally torn apart by the body it is orbiting. A real satellite can pass well within its Roche limit before being torn apart.
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When is Roche limit reached?
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It is reached when a loose chunk of material of mass μ is tidally attracted to M more than it is gravitationally attracted to m.
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What is interesting about the Earth's Moon?
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The period of rotation and the period of orbit around Earth is the same: 27.3 Earth days. The Moon follows a nearly circular path about the Earth. This orbit is located 30 Earth diameters away from Earth. The pull on the Moon's mass (1.2 % of Earth) causes the Earth to wobble in its orbit about the Sun. It is the center of mass of the Earth--Moon dumbbell that follows a smooth course about the Sun.
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Describe 4 theories for the formation of the moon.
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1.CAPTURE. Moon was a rock that was flying by and got in the orbit. Composition of moon and earth can be quite different.
2.FISSION. When Earth was still molten, some part left and became moon. This is physically possible but requires: Composition of moon and earth's mantle are similar; and the earth/moon protoplanet have a very rapid rate of rotation (that is 2 hours) 3.BINARY ACCRETION. Requires that composition of moon and earth be essentially the same. 4.COLLISION. Earth must have been spinning really fast. Requires composition of moon and earth's mantle be similar; but with moon depleted in volatiles since the collision would have raised ejected debris to high temperatures that would have probably led to loss of volatile elements. |
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Describe Moon's composition.
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-relatively light compared to Earth
-density is chondritic -depleted in iron relative to Earth -believed to have a very small core |
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Explain how the theories eliminate.
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#3 eliminates because composition of the moon and earth are not the same. Moon has crust, upper mantle, moonquake zone and core only. It is simpler.
#1 eliminates because the Earth and moon are formed from the same material. #2 eliminates because the rotation rate is too slow. Has been 6 hours for 4 billions years ago (for both Earth and Moon) Earth's rotation was never too fast enough to spin off the moon. |
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Which theory is favored?
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#4 COLLISION. Because the moon shows a consistent tendency to be depleted in volatile elements. Most support for collision theory comes from an analysis of orbital properties of Earth moon system.
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Explain Oxygen Isotopes.
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-There are 3 stable isotopes that behave chemically as oxygen, but differ only in their masses (that is different number of neutrons)
-Their relative abundances vary slightly from sample to sample within the Earth (or any other confined pool of O) due to fractionation processes. -(small)16O is the most common, (small)17O has typical abundance of one atom in 2500 O atoms, and (small)18O has typically one atom is 500. These slight variations are used by geochemists to determine the source and origin of the samples. |
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What is mass fractionation?
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It is typically expressed relative to most abundant form of O (that is (small)16O.
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What is mass dependent fractionation?
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The larger the difference in mass between a pair of isotopes, the easier they are to separate.
-enrichment/depletion of (small)18O by a mass-dependent process-fractionation process is twice the enrichment (or depletion) in (small)17O, since mass difference between (small)18O and (small)16O is twice that between (small)17O and (small)16O. |
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What is an example of a process which produces mass dependent fractionation?
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Evaporation of water: the heavier isotopes (small)17O, and especially (small)18O, are harder to evaporate, so water vapor is depleted in the heavier isotopes, and the residual liquid is enriched in the heavy ones. For this reason rainwater is isotopically lighter than seawater.
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What are 2 peculiarities of orbital properties of Earth Moon system?
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1. Moon's orbital period and rotational period are the same.
2. Moon's orbital radius increases at a rate of 4 cm/yr because orbits the same side as the Earth. |
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Know the phases of the Moon.
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A. New
B. Waxing crescent C. First quarter D. Waxing gibbous E. Full F. Waning gibbous G. Third quarter H. Waning scresent |
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What is sidereal month?
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The moon appearing to move completely around the celestial sphere once in about 27.3 days as observed from the Earth and reflects the corresponding orbital period of 27.3 days.
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What is synodic month?
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The moon taking 29.5 days to return to the same point on the celestial sphere as referenced to the Sun because of the motion of the Earth around the Sun.
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Describe the movement of the Moon each day.
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With respect to the background constellations the Moon will be about 13.2 degrees further East each day. (must move Eastward among the constellations enough to go completely around the sky (360 degrees) in 27.3 days.)
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What causes Earth to bulge?
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Moon's gravitational attraction. So moon produces tides since the bulge is more pronounced over ocean.
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What does the bulge on the moon do?
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It slows the rate of rotation of the Earth and moon; and increase the energy of the orbit (that is higher orbital distance and longer period of orbit).
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What does the tidal coupling of Earth-Moon System do?
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-slows rotation because differential strength of forces
-increases angular momentum of moon's orbit because differential strength of forces -increases orbital period bc of Kepler's Law. Since you're increasing angular momentum and maintaining Kepler's Law, velocity needs to be decreased while radius needs to be increases which increases the period. |
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How does the tidal bulge slow the Earth's rotation and causes the Moon's orbital radius and orbital period to increase?
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Moon pulls on Earth's tidal bulge to slow Earth's rotation and Earth's tidal bulge pulls the moon ahead in its orbit, and Moon's orbital radius increases.
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What is the results of tidal drag (tidal coupling of the Earth-Moon)?
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Synchronization of Earth and Moon. Although not complete, the Earth is slowly decreasing its rotational period and eventually the Earth and Moon will have exactly the same rotational period, and these will also exactly equal the orbital period. At the same time, the separation between the Earth and Moon will slowly increase in just such a way as to conserve angular momentum for the entire system.
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What is the current rate of orbital retreat of moon?
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4cm/yr
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In about 10 billion years, what will the solar day and lunar month be?
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60 days
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What has the average rate of retreat over lunar lifetime have been?
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10cm/yr
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When were the moon and Earth essentially touching?
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4 bil years ago
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What is the Moon Formation Theory?
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At the time Earth formed 4.5 bil years ago, other smaller planetary bodies were also growing. One of these hit Earth late in Earth's growth process, blowing out rocky debris. A fraction of that debris went into orbit around the Earth and aggregated into moon.
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What are moon's two crustal components?
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1. Maria (basaltic, 3.1-3.9 bil years old, mostly on nearside of moon, relatively thin)
2. Highlands (granitic, 4 bil years old, relatively thin) |
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Describe the basic theory of moon geology.
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Moon was molten when or soon after it formed. It differentiated into small core and mantle and outer crust that is currently the moon's highlands. Meteoritic bombardment created craters and cracks through which volcanic eruptions gave rise to mare which is mostly on nearside because bulging from Earth made lunar crust thinner on that side and more amenable/willing to eruptions and lava flows. But volcanic activity ended about 3.1 billion years ago as moon became geologically dead (it's smaller than Earth so much less radioactive and it's tectonically dead)
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Is there water on the moon?
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Yes, in 1994 by the Clementine spacecraft, they revealed that deposits of ice exist in permanently dark regions near the south pole of the Moon. Initial estimates suggest that the volume of a small lake exists: ~1 billion cubic meters.
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What is Near-Earth Objects (NEOs)?
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comets and asteroids that have been nudged by the gravitational attraction of nearby planets into orbits that allow them to enter the Earth's neighborhood.
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Describe comets.
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-composed of mostly water ice with embedded dust particles
-originally formed in the cold outer planetary system -the giant outer planets (Juniper, Saturn, Uranus, and Neptune) formed from an agglomeration of billions of comets and the left over bits and pieces from this formation process are the comets we see today |
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Describe asteroids.
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-rocky (chondritic)
-formed in the warmer inner solar system between the orbits of Mars and Jupiter -Asteroids are the bits and pieces left over from the initial agglomeration of the inner planets that include Mercury, Venus, Earth and Mars. |
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What are the evidence of impacts?
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-craters which are commonplace on Moon, Mercury and Mars but rare of Earth because the Earth crust is very dynamic with ocean, tectonic, volcanic and etc.
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How do you distinguish meteorite craters from volcanic craters?
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By geology and Iridium
-volcanic craters are lava rock, volcanic ash -meteorite craters are shocked quartz, tektites; it is dark-colored, rounded silicate glass particles several cm in size and often aerodynamically shaped |
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What are tektites?
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Glassy objects that are thought by most scientists today to be melt products of terrestrial rocks.
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What is Iridium?
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A sensitive tracer of extraterrestrial matter. It is strongly depleted in the Earth's crust (0.05 ng/g) compared to chondritic abundance (500 ng/g). Most of the Earth's Ir is probably stored along with Fe in the core.
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Know the impacts within 1km/2km/5km/10km of:
a-kinetic energy (millions of megatons of TNT) b-avg impact interval (years) c-crater diameter (rim to rim) d-blast radius for 4psi overpressure [500km/hr winds] e-dust and debris fallout f-earthquakes, hurricanes and tsunami (hrs ot months) g-dark skies and cooling from dust, soot and oxides of sulfur. h-global greenhouse heating from water and CO2 i-plant growth and extinctions |
a-0.1km/1km/10km/100km
b-200,000km/500,000km/10mil km/100mil km c-24km/46km/100km/200km d-130km/180km/470km/1800km e-300km/400km/1100km/4000km f-regional/regional/global/global g-regional freezing for weeks, moderate global effects for weeks/skies darker than darkest cloud cover, global drop of 8C for weeks then moderate global effects for months (no summer)/severe global effects, day becomes night for months/very severe global effects. day becomes night for months, freezing conditions away from coastlines.) h-negligible/minor for years/moderate for decades/major for centuries i-disrupted for month. some global crop failures/disrupted for years. some regional extinctions. global crop failures/photosynthesis stops for months. decades for plants to recovers. major regional extinctions/hundreds of years. global mass extinction. |
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What are the duration of effects for:
a-darkness b-acid rain c-ozone depletion d-climate disruption |
a-6 months
b-1 year c-10 years d-1,000,000 years |
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Name 5 major extinction events. For how long?
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-Late Cambrian
-Late Ordovician -Late Devonian -End Permian -Late Triassic -End Cretaceous ~25 million year periodicity |
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Explain K-T Boundary Impact (Cretaceous-Tertiary).
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-by Alvarez and Alvarez in 1980
-found an outcrop of rock deposited in the deep ocean where the K-T boundary was well exposed and paleontologists were sure it was properly identified -boundary was clearly marked out by the disappearance of many kinds of Cretaceous microfossils, particularly most foraminiferans -at the boundary is a think layer of brown and black clay so Alvarez group sampled carefully through this rock section and analyzed for Ir -it was more than 150 km across, it produced mass extinctions (10km across min) -high Ir content of sediments led Alvarez group to conclude that a major impact occurred at the K/T boundary -found more supporting evidence by finding Ir enhancement globally at KT boundary |
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Explain Chixculub Impact Site.
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-Chixculub=multi-ringed structure
-impact basin is buried by several hundred meters of sediment, hiding it from view. -NASA believe that an asteroid 10-20km in diameter produced this impact basin -asteroid hit a geologically unique, sulfur-rich region of the Yucatan Peninsula and kicked up billions of tons of sulfur and other materials into the atmosphere -darkness prevailed for about half a year after the collision which caused global temperatures to plunge near freezing. half of the species on Earth became extinct, inc. dinosaurs. -one considerable cause of extinction at the end of the Permian |
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What would the effects of the asteroid impact that resulted in the Chixculub crater be?
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-catastrophic
-sent huge shock wave around the globe as it slammed into Earth = huge nuclear explosion -immense heat and winds would have set off widespread fires, perhaps of global proportions, burned for weeks -earthquakes and huge tidal waves buckled and buffeted the Earth's surface while a cloud of vaporized water and rock would have thrown up into the atmosphere -cloud of debris could have caused months-years of darkness, acid raid, and global cooling/warming -effect on life devastating, particularly for larger organisms, or those dependent on plant-life for food |
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Explain Shiva Impact.
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-by Sankar Chatterjee in 2009
-500km crater in India -identified underwater mountain called Bombay High, off the coast of Mumbai, that formed right at the time of the dinosaur extinction. measures 5km from sea bed to peak and surrounded by Shiva's crater rim -analysis shows that it formed from sudden upwelling of magma that destroyed Earth's crust in area and pushed mountain upwards in hurry. -argues that no force other than rebound from impact could have produced this kind of vertical uplift so quickly. The blow that caused it would surely have been powerful enough to smash ecosystems around the world. |
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Explain Tunguska Impact.
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-1908 hundreds of square miles of Siberian forest were flattened and burned by a mysterious fireball
-vast fireball raced through the dawn sky over Siberia, then exploded with the force of 1000 Hiroshima bombs -heat incinerated herds and reindeer and charred tens of thousands of evergreens across hundreds of square miles. -for days and for thousands of miles around, the sky remained bright with an eerie orange glow -effect was much like that of great volcanic eruption but no eruption -only objective indication of extraordinary event was quiver on seismographs in Siberian city of Irkutsk, indicating a moderate quake some 1000 miles north in Tunguska region |
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What is the Cambrian explosion?
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A period in which life on Earth took off with a dramatic burst in the number and diversity of species.
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What is pros of impacts?
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-additional stress of the impacts forced life to become more diverse and flexible. The stress caused by catastrophic impacts may have forced evolution into new directions.
-may have contributed to creation of life |
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What is a PHA?
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It is Potentially Hazardous Asteroids which are currently defined based on parameters that measure the asteroid's potential to make threatening close approaches to the Earth.
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What is MOID?
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It is Minimum Orbit Intersection Distance.
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What are considered PHAs?
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all asteroids with an Earth MOID of 0.05 AU or less and an absolute magnitude (H) of 22.0 or less = asteroids that can't get any closer to the Earth (that is MOID) than 0.05 AU or are smaller than 150m in diameter.
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What are not considered PHAs?
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H=22.0 with assumed albedo of 13%
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How many known PHAs are there?
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1244 and increasing all the time.
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What are the odds of dying from asteroid, comet and meteorite impact?
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1 in 20,000. Only smaller than car accident, murder, fire, firearms accident and electrocution.
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Where did the H in the Earth's water come from?
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-H is a volatile element and it is highly depleted on the Earth relative to the solar composition of carbonaceous chondrites
-This is consistent with the K/U ratio on Earth which suggests that volatiles are generally depleted on the Earth and with the notion that shortly after Earth formed that planet differentiated into core/mantle/crust/atmosphere and most of this early atmosphere was blown away by bombardment of asteroid and comets |
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What are the basic principles needed to know to review how atoms in the atmosphere escape to space?
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1.escape velocity
2.temperature - macroscopic measure of avg random kinetic energy of the material in question 3.molecular motion - molecules have a "distribution" of velocities centered about this avg velocity -as temp increases the probability of finding molecules at higher energy increases |
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Why is there so much H?
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Accumulation of water from continuous bombardment of cometary material after the formation of moon.
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How do atoms in the atmosphere escape to space?
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-atom/molecule must not collide with another atom/molecule before it exits that atmosphere
-frequency of collisions is proportional to the atmosphere's density--the less dense the atmosphere, the fewer collisions |
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What is exosphere?
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It is the part of the atmosphere where collisions are so infrequent that molecules follow ballistic trajectories. In the region, a molecule with a velocity greater than escape velocity will in fact escape to space.
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How does a molecule get a velocity greater than escape velocity?
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through a collision with another molecule. If that collision sends the molecule in an upward trajectory with a velocity > escape velocity, it will escape to space.
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How many H atoms have velocities above escape velocity?
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1 in 1000
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What saves the Earth's H?
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-how much H2O gets into the stratosphere
-Virtually all H in atmosphere is present as H2O bc of free O left in mantle so for H to escape, H2O must be broken down into H but that requires highly energetic photons from the sun to not penetrate below the stratosphere. -rate of H escape depends upon how much H2O gets into the stratosphere and how fast it is dissociated. |
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How much H2O gets into the stratosphere? (2)
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Not much bc:
-H2O has a very special property (it does not exist as a vapor as Temp decreases) -Atmosphere has a special property (temp minimum at tropopause |
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What is the time required to convert a stratospheric H2O molecule to H and transport it to the exosphere?
What does this imply? |
~1.6 x 10^4 years which is much longer than the time for H to escape from the exosphere and implies that the time for H to be depleted in the Earth is ultimately controlled by the rate of H supply from the stratosphere and not by the lifetime of H in the exosphere
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How long will it take for all the Earth's water to escape?
What does this imply? |
~8 trillion years (8x10^12 years)
-this is longer than the age of the Earth and thus H is not significantly depleted on the Earth and as a result the planet has a sufficient supply of water to be habitable. |
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What must happen for H to escape?
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it must be photolyzed from H2O which required transport to upper atmosphere where the hard UV radiation can photolyze H2O
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What does cold temperature at top of troposphere do to water?
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it traps it.
-as water vapor rises in the troposphere, cold temperatures cause condensation/deposition and precipitation |
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How much of H2O can reach the upper atmosphere where photolyzation can occur?
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very minute amounts
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After photolyzation, how can some H escape?
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some H can accelerate to escape velocity in exosphere to escape.
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For life to have evolved and survived on the Earth, liquid water is needed. This implies
0 C < Surface Temperature < 100 C. How, why? |
The Earth found itself in just the right place in the solar system. Goldilocks theory explains that Venus is too hot, Mars is too cold and Earth is just right.
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Explain "Blackbody Radiation."
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ideal black body absorbs all radiation incident on it and radiates the maximum radiation possible.
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Know the 4 basic concepts:
1. Electromagnetic Radiation 2. Electromagnetic Spectrum 3. Radiative Flux 4. Blackbody Radiation |
!
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What is Planck Function?
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blackbody radiation curve
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What is the key concept of effective temperature?
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-avg temp of a body at which it radiates energy
-for a planet it is also the temp the planet would have if it behaved as a Blackbody |
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How can you calculate a planet's effective temperature?
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By demanding a simple energy balance.
energy absorbed per unit time = energy emitted per unit time |
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What is albedo? Give the formula. Give the variation #.
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the reflectivity of a planet surface.
[reflected light]/[incident light] can vary from ~0.05-0.85 |
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what is planetary albedo?
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"area-weighted" average of the albedo's of each surface type on the planet.
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Why is Earth not an ideal blackbody?
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-the planet's surface is reflective and the reflectivity of a planet reduces the amount of energy absorbed by the planet.
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How can planet's have temperatures above effective temperature?
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if they have an atmosphere with the proper radiative properties which can give rise to greenhouse effect.
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Define Greenhouse Effect.
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It is responsible for raising Earth's surface temperature from about 255K (modified effective T) to ~288K. It makes Earth habitable.
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What are the Earth's Greenhouse Gases?
which one is the most important? |
-H2O, O3, CO2
-H2O |
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What is the habitable zone?
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-The radial zone of planetary orbits that are close enough to a star for the energy of that star to drive the chemistry of life (and cause water to be in liquid state) -- but not so close as to boil off water or break down the organic molecules on which life depends.
-habitable zone first encompassed the orbits of Venus to Mars, planets close enough to the sun for solar energy to drive the chemistry of life--but not so close as to boil off water or break down the organic molecules on which life depends. -but habitable zone may be larger than originally conceived. the strong gravitational pull caused by large planets may produce enough energy to sufficiently heat the cores of orbiting moons. |
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Where is the habitable zone?
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generally thought to be in the range from Venus to Mars in our solar system. from ~0.95-2AU.
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Why is the presence of a large outer planet such as Jupiter critical?
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it is theorized that the bombardment of comets may have been caused by gravitational influence of large outer planet. The need for a large outer planet (outside the habitable zone) greatly reduces the probability of there being other habitable planets. Juniper is critical bc it may now be acting as a gravitational shield hence the reason why Earth has not been impacted by comets since the impact of comets.
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Who is Neil Degrasse Tyson?
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He wrote the Goldilocks and the Three Planets.
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What is the Goldilocks problem?
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-Venus, Earth and Mars all started with about the same composition.
-all are, more or less, within the solar system's "habitable zone." The combination of solar heating and greenhouse effect should in principle be able to make all 3 planets habitable -BUT, only Earth's climate follow a habitable path while Venus became too hot and mars became too cold. |
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Compare Earth vs. Venus vs. Mars on radius, amt of volatiles, atmosphere, avg. mass, mass of atmosphere, temperature
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-radius: Earth and Venus about same size but Mars smaller
-amt of volatiles: Earth and Venus about same size but Mars smaller and started with less volatiles -atmosphere:Venus has denser atmosphere while Mars atm very thin -avg. mass: Mars and Venus similar -mass of atmosphere:Venusian atmosphere much heavier while Mars atm disproportionally smaller -temperature:Venusian atmosphere very hot while Mars atm very cold |
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compare Earth vs. Venus vs. Mars on atmospheric composition on N2, O2, CO2, H2O.
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-N2: major constituent of Earth's atm; Mars and Venus similar
-O2: not found in Venus but small amt found on Mars -CO2: major constituent of Venus and Mars' atm -H2O: water in all three planet's atm's but Venus and Mars more similar to each other |
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Does Venus have more C than Earth?
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-No.
-Most C on Earth is locked in carbonate and organic sediments which is not the case for Venus which does not have ocean and life. -total abundance of C are same |
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Why is Venus so hot?
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Having this much CO2 in the Venus atmosphere could raise the surface temp from ~300 to ~700K.
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Is the amount of H2O and H on Venus and Earth the same?
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No. While H2O and H on the Earth is in oceans and lithosphere, most of H2O and H on Venus is in the atmosphere. Therefore, there isn't more H2O in hot Venus atmosphere.
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What happened to Venus' H?
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-lose most of H
-deuterium/hydrogen ratio (2H/1H) -implication that Venus lost most of its H to space via a mass fractionation process -high temp in Venus atmosphere eliminates cold trap and allows H2O to get into upper atmosphere in large quantities and when H2O gets into the upper atmosphere, it is quickly dissociated and the H quickly escapes to space. -temp on Venus remain above boiling point for much of the atmosphere |
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Describe Runaway Greenhouse Effect on Venus
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-what happened on Venus
-Venus starts out warmer than Earth -> more water vapor gets into the atmosphere which raises temp even more which puts water vapor in atmosphere -unlike Earth, this positive feedback never stops and all H2O on Venus evaporates -cannot form carbonate in ocean in either forms of carbonate rock or atmospheric CO2 -high temps bake the CO2 out of the carbonates so all C on Venus ends up in atmosphere -eventually H2O is depleted via H escape and loss of atmospheric H2O does not prevent hot atmosphere bc of all the CO2 is in the atm |
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Why is Mars so cold?
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-mass of Mars is ~1/10 that of Venus but mass of atm CO2 of Mars is smaller than mass of atm CO2 of Venus
-unlike Venus, most of the C on Mars is not in the atm as CO2, but instead is locked away in the solid part of the planet -even though the CO2% in Martian atmosphere is large, mass is much less than that of Venus and there is very little water, hence little or no Greenhouse effect -Like Earth, Mars at one time had a fairly strong Greenhouse Effect that made it possible for liquid water to have existed on the surface. |
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Describe Martian atmosphere and how it relates to Greenhouse Effect.
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-have very little H2O and moderate amt of CO2 = relatively small Greenhouse Effect
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How was Mars different before?
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Mars used to have a vast ocean in the north and valleys around the equator, suggesting that the planet once had a humid, rainy climate.
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How did Earth manage to use its Greenhouse Effect to maintain habitable temp but not Mars?
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Earth has developed a mechanism that:
1.allows CO2 to be constantly recycled back to the atmosphere 2.acts as a thermostat that stabilizes temp -Earth has plate tectonics but Mars does not. Mars is not tectonically dead. |
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How can plate tectonics on Earth keep Greenhouse on Earth active?
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-when liquid water exists at the surface, weathering, calcite prod, opal prod or metamorphosis in mantle can occur.
-1. CO2 removed from the atmosphere by rain/weathering -2. CO2 returned to atmosphere by sedimentation and metamorphosis -This cycle can stabilize climate: climate gets colder/warmer; less/more rain; slower/faster weathering; more/less CO2 in atm; climate gets warmer/colder |
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What is the short team carbon cycle?
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You get sources of CO2 through decay (decomposing animals/vegetation; combustion of Carbonaceous material) or respiration (exhaust from metabolic processes)
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Describe dissipating Greenhouse Effect on Mars.
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-Mars probably started with a much denser and warmer atmosphere
-there are channels that look like dried river beds on Earth. It is very likely that these were formed by liquid water which can only exist at atmospheric pressures much higher than the present value -when planet became tectonically dead, abundance of atmospheric CO2 began to fall as carbonate deposits increased -Greenhouse effect became weaker and atmosphere cooled -eventually temperatures became so low that atmospheric water and then CO2 itself began to freeze out of the atmosphere -Greenhouse effect became weaker still and temperatures fell even more |
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Why is Earth habitable and Mars and Venus are not?
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-Earth was far enough away from sun to avoid a runaway Greenhouse Effect
-Early in Earth history, solar output was less and atmosphere must had a stronger Greenhouse effect but as output increased Greenhouse effect must have gotten weaker -Earth was large enough to remain tectonically active to maintain and regulate CO2 abundance in atmosphere. |
