Earth Science Final Notes.docx

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Department
Earth Sciences
Course
Earth Sciences 1086F/G
Professor
Wendy Pearson
Semester
Fall

Description
Chapter 10: Venus • Introduction o Morning star/evening star  Normally only see it for about 3 hours after sunset and 3 hours before sunrise and it is brighter than any object besides the moon o Named after the Roman goddess of love and beauty o Thick atmosphere o Venus Express  Caused us to readjust many of the theories we knew from previous data about Venus  Determined that large volumes of the atmosphere are escaping into space o 23 spacecrafts have flown past or orbited Venus and over a dozen have landed on the surface  The surface is drier than any desert on Earth and two times hotter than a hot kitchen oven • Basic planetary facts o Close to earth’s size, mass, gravity o Second closest planet to the sun and our nearest planetary neighbor o Orbit about sun 225 days, and distance form the sun being almost three-quarters of Earth’s distance o Elliptical orbit—most circular of any planet  Orbital path lies almost in the same plane as Earth’s o Commonly called Earth’s twin o Rotation appears retrograde (clockwise), but only because it was knocked over by large impact o Very slow rotation (243 Earth days)  Slowest spinning object in the known universe o No satellites o Small magnetic field produced by atmosphere interaction with solar wind o Winds at the surface are relatively gentle and faster winds are higher up o Surface  Relatively few impact craters and very few small impact craters; they are all medium to huge (result of the dense atmosphere, small objects just burn up in it)  Craters that can be seen appear young, rarely filled with lava, indicating there were formed after a ‘recent’major volcanic activity  Suggests surface is young, about 500 million years old but the planet itself is about the same age as Earth (4.5 billion years old)  Very small volcanoes and immense volcanoes • Atmosphere/greenhouse/hydrosphere o Completely covered with a thick black blanket of clouds (consisting primarily of droplets of liquid/solid sulfur and droplets of sulfuric acid) o Below the sulfuric acid layer, the thick atmosphere is composed mainly of 96% carbon dioxide; this is the secondary atmosphere produced by intense volcanism  3.5% nitrogen  0.1-0.4% water vapour o Atmospheric pressure on Venus is 90 times greater than of Earth’s surface o No water on surface now, but before intense greenhouse probably had abundant liquid water (evidence deuterium/hydrogen) o Atmosphere so thick, pressure at surface crushingly high o Venus Express shows cyclonic storms o Greenhouse effect 1  Carbon dioxide is pretty transparent to in-coming light energy but fairly opaque to out-going infrared light energy  Any greenhouse effect begins with incoming short wavelength light energy from Sun warming a planet’s surface, but ends up with a surface or near-surface growth of heat because of the inability of the long wavelength infrared energy to escape a CO2 rich atmosphere and get back out to space. It so happens that the wavelengths of radiated energy that CO2 does allow to escape back into space from a planet surface are blocked by water and sulfur dioxide  Although there is not a huge amount of either in the Venus atmosphere, it’s quite enough to strengthen the greenhouse effect very, very substantially. The end result is that Venus has a fairly uniform surface temp of about 462 degrees Celsius o No ozone layer to protect the atmosphere from UV radiation, which caused the atmospheric water to break up and lost most of the hydrogen to space  Now it is a deadly dry world with only enough water to make an ocean 0.3 meters deep o **If all of the carbon dioxide in Earth’s rocks was put back into the atmosphere, our air would be as dense of that as Venus, and we would suffer from a severe greenhouse effect** • Geology o Few impact craters, thus surface has been resurfaced (by basalt lava flows) o Surface dominated by volcanic features  Coronae • Thought to be formed by mantle plumes that bring magma right up under the crust and then partially subside  Pancake volcanoes • Appear as flattened domes and are thought to be formed by viscous magma, flattened by the high atmospheric pressure • Common to find groups of hundreds of these in areas called shield fields  Immense volcanoes o Much tectonic activity, but no evidence of plates (probably mantle plumes) o Unexpectedly sharp geological features like knife sharp mountain ridges and cliffs that show absolutely no sign of erosion  Rocks must be much stronger than on earth because they have no water content  There is visual weathering/erosion evident—wind produced o Interior  Overall density suggests that the interior must be a mix of hot rock and metal much like Earth • Four stages of history 1. Differentiation (separation of material according to density) 2. Cratering (a period of violent impacts) 3. Flooding (not by water but lava flows) 4. Slow surface evolution • Main difference between Earth and Venus is the lack of water on Venus • Venus lacks tensional crust rifts, and its numerous volcanoes cannot carry much of the heat out of the interior o Seems to get rid of its heat through large currents of hot magma that rise beneath the crust Chapter 11: Mars • Planetary facts o Canali: artificial lines across so-called desert regions that turned out to be nothing more than tricks of the eye 2 o About half the size of Earth “smaller brother of Earth” o Much lower density than Earth, LOW escape velocity o Nearly the same obliquity, tilt and rotational period as Earth o Two satellites (both irregular and tidally locked to Mars)  Phobos: closest natural satellite to any planet in the solar system, small, rocky  Diemos: 3 times as far from Mars, small, rocky, no grooves  Demonstrate 3 principles: 1. Some satellites are probably captured asteroids 2. Small satellites tend to be irregular in shape and heavily cratered 3. Tidal forces can effect small moons and gradually change their orbits • Missions o On surface  Curiosity • Described by NASAto be better than any other rover on Mars; designed to travel over rougher terrains, dig deeper, travel further and faster • Primary objectives: see if Mars had microbial life, explore the presence of water, Martian climate and Martian geology  Opportunity • Still going along collecting info, but its robotic arms are partially seized  Pheonix Lander o In orbit  Mars Odyssey  Mars Express  Mars Reconnaissance  Orbiter o Spirit: Stuck in a sand trap, mission now over, was supposed to have a short lifetime but made very many accomplishments Weather andAtmosphere o Now 95% carbon dioxide; very low pressure (i.e., very little atmosphere) ii. 3% nitrogen iii. 1% argon iv. Miniscule traces of water vapour and oxygen o Air is thin, dense enough to be visible in oblique angle photos o Occasional weather patterns are visible o Previously had lots of atmosphere—enough for a greenhouse to support liquid water on surface o Cold, dry, but has some (rare) scattered clouds of ice crystals o Fairly strong winds; erosion by winds; fields of sand dunes o How much atmosphere a planet has depends on how rapidly it releases internal gas and how rapidly it loses gas from its atmosphere o The rate at which a planet loses gas depends on its mass and temperature o Gas atoms can escape from Mars MUCH more easily than they can escape from Earth o Does not currently have a magnetic field and the atmosphere is thin, the solar wind interacts directly with both the Martian atmosphere and the planet surface o Polar hood: CO2 clouds and haze/CO2 ice particles Water and ice o Permanent polar ice caps; permafrost; water chemically bound in mineral/rocks; very little in 3 atmosphere o Once had abundant liquid water that carved great gullies, made large and deep oceans, produced very large volumes of sedimentary rocks and minerals Geology o No evidence of plate tectonics o One-plate planet and includes some of the largest volcanoes in the solar system o Southern highlands are heavily cratered, which must mean that they are 2-3 billion years old o Northern lowlands are smooth and so remarkably free of craters that the lowlands must have been resurfaced roughly a billion years ago o Evidence suggests the lowlands were once filled by an ocean of liquid water o Largest volcano in the solar system (Olympus Mons); shield type—may be from mantle plume feed; volcanism rare for last few millions of years because planet so small it is cooling quickly o Possible some volcanoes are still active o The Martian volcanoes are shield volcanoes (shaped like an inverted warrior shield; formed by low viscosity lava flows) o Vast expanses of layered sedimentary rock indicate previous large oceans o Salt (evaporite) minerals are also proof of water; basalts contain roughly same amount of water in them as those on Earth o Red beds: Red colour of most surfaces: caused by the mineral hematite—which is a reddish iron oxide (indicates oxygen taken up by iron of rocks as they weather) o Blueberries: small spherules scattered over some areas of soil. Called blueberries because they are a blue- grey colour o Saltation: The movement of hard particles over an uneven surface in a turbulent flow of air or water o Dune fields, or large masses of wind-sculpted dunes, are common on both Earth and Mars o Asystem of enormous faults (4 times deeper than our Grand Canyon and 4000 km long) shows crust once very active) o Valles Marineris is a network of canyons that stretches 4000 km long and up to 600km wide o The silicon content of some of the rocks is much higher than that of the Martian meteorites (basalts) which were all igneous o The igneous rocks analyzed by Pathfinder are not basalts o Their silicon content classifies them as andesites o Of course, many of the rocks seen on the surface are not volcanic at all—just sedimentary o Duricrust: a hard crust formed at or near the surface of the ground as a result of the upward migration and evaporation of mineral-bearing ground water Interior o Core not quite solid, but very viscous and cooling o Crust has become thick over time o Mantle likely penetrated locally by plumes o The plains of the western hemisphere of Mars are dominated by the Tharsis dome (surmounted by the huge volcano Olympus Mons and other shield volcanoes rising above 20 km above the mean surface) History o Noachian Era: Earliest period of Martian history, believed to be characterized by a thicker early atmosphere, high rates of cratering, heat flow, volcanism, fluvial activity, and probable glacial activity. It lasted from planet formation 4.5 billion years ago until about 3.5 billion years ago. The latter date is fairly well constrained because it has to fall within the end of the early intense cratering; the uncertainty on the end date may be a few hundred million years. o Hesperian Era: Era of transition from Noachian conditions to modern Amazonian conditions. In many of the major outflow channels, the last water flows and erosion episodes probably dated from this period. It probably 4 lasted from about 3.5 billion years ago until roughly 3.3 billion years ago. o Amazonian Era: The modern, dry, dusty, mostly frozen era. Lasted from roughly 3.3 or 2.9 billion years ago until the present. Although geologic activity has declined on Mars, evidence has been found of active geology (lava flows, water release) in this era. Four-stage history: 1. In the first stage of planetary evolution, the planet seems to have differentiated into a core, mantle, and crust. There are no obvious traces of plate tectonics such as folded mountain ranges. Mars lacks a magnetic field, so its core cannot contain much molten iron. The Mars Global Surveyor spacecraft has detected traces of residual magnetic fields trapped in parts of the crust, and that suggests that Mars once had a magnetic field and presumably a molten iron core. 2. During the second stage of planetary evolution, cratering, the crust of Mars was battered during the heavy bombardment as the last of the debris in the young Solar System was swept up. The old southern hemisphere survives from this age about 4 billion years ago. The largest impacts blasted out great basins. 3. The third stage of planet formation, flooding, included flooding by great lava flows that smoothed some regions. The evidence that the flooding stage included not only volcanic magma but also water seems quite impressive. 4. The fourth stage of planet formation is unremarkable on Mars. The crust of Mars is now too thick to be active. The planet has lost much of its internal heat, and now it lacks much of a molten core, as evidenced by the lack of a planet-wide magnetic field.Although the crust was stressed by rising magma, it is too thick for plate tectonics. Unit 4 Introduction o Discovery of Ceres o Discovered in 1801 by Guiseppe Piazzi as the first object in space o Now classified as a dwarf planet o Definitions o Asteroid: a natural rocky object in space measuring 100 m to several hundred kilometres in diameter. o Meteoroid: a natural rocky object in space measuring from a few millimetres to 100m in diameter. o Meteor: the visual streak of light associated with passage of a small meteoroid through Earth’s atmosphere; the heat energy producing the light is a result of friction between the object and molecules of gas in the atmosphere. Remember – a meteor is not the object, only the light phenomenon. o Fireball: the light associated with a large meteoroid or asteroid as it interacts with the atmosphere. o Meteorite: a fragment (any size) of either a meteoroid or asteroid that lands on Earth’s surface. Please remember – it is not called a meteorite until it actually lands on surface. o The Titus-Bode Law/rule o Need to remember basic math** o Take the simple mathematical series 0, 3, 6, 12, 24, etc. (note that each successive number is double the previous) o Add 4 to each of the above, getting: 4, 7, 10, 16, 28, etc. o Now divide each of the numbers by 10 to get 0.4, 0.7, 1.0, 1.6, 2.8, etc. these are the predicted planet spacings inAstronomical units (AU) Chapter 12:Asteroids o Main Asteroid belt o Appears almost empty o Location  Gap between Mars and Jupiter o Influence of Jupiter 5  In the early solar system, the asteroids were distributed more or less uniformly within the solar system and now Jupiter’s large mass has a great gravitational force that caused the asteroids to motion the small bodies towards it  2 major gravitational forces acting on asteroids: • Jupiter • Sun  Collisions occur and fragments get kicked out of the belt and most meteorites originate with those fragments o Why the gaps o Classification: “Kirkwood gaps”  Noticed that the differences between gaps corresponded to simple fractions of the orbital period of Jupiter o 1. Classification based on meteorite samples of the asteroids  93% composed of silicates and most of the rest pure metal o 2. Base classification upon the characteristics of sunlight reflected off the surfaces of asteroids—looking loosely at albedo (proportion of light reflected from an object; the range is 0 (perfectly black) to 1 (perfectly reflecting)) of the object o 3. Astronomers and scientists have constructed pretty sophisticated instruments which break down the reflected light into a whole spectrum, thus collecting rough element analyses of surfaces as well as simple albedo numbers o 3 main groups o C-type asteroids: high carbon content (75% of know asteroids) roughly similar composition to the sun o S-type asteroids: high silicon (17%) o M-type asteroids: metallic (most of remaining) o How do we get the composition? o o Does the distribution of asteroid types match distribution of meteorite types collected on Earth? o o Note location of most C-rich o Middle to the out ridge of the belt o Families o Cratering studies show that the smaller projectile experiences far greater stresses than the larger target body o Hirayama surmised that the breakup of an asteroid into a collection of fragments, which he called a family, would result in similar orbital characteristics for these bodies o He was able to recognize clusters of asteroids which we now refer to as Hirayama families o He hypothesized that the members of any one family were collisional fragments of the same original planetesimal o 19 families have been defined o Non-belt asteroids o NEAs/NEOs  All follow highly elliptical orbits, and they are subdivided into categories according to the dimensions of their orbits  All NEAs have unstable orbits  Atens: most of these asteroids have orbits less than 1AU—which means they orbit within the 6 orbit of Earth  Apollos: most have an orbit that brings them through the orbit of Earth (cross its path)  Amors: commonly cross the orbit of Mars but don’t cross with Earth’s even if they get close  Dangerous because they interact with the gravitational influences of the planets  Earth is hit by an Apollo object once every 250,000 years on average  Many dozens of Apollo objects have known orbits, and none of those will hit Earth in the immediate future o Trojans: Trojan asteroids are a very large group of asteroids that share an orbit with Jupiter. Each of the Trojans liberates around one of two of the Lagrangian points L4 or L5 which are 60° ahead of and behind the planet. o PHAs: Potentially hazardous asteroids. Minimum of 150m in diameter and comes closer than 0.05AU to Earth o Impact risk and the Torino scale o Torino scale: Ascale used to rate the power and likelihood of an asteroid strike onto the planet Earth (0-10 scale) o 4179 Toutatis (the doomsday asteroid) every 4 years its orbit either comes close or crosses Earth’s orbit o Asteroid exploration o Eros: NEAR Shoemaker first spacecraft mission specifically designed to study an asteroid; first time a spacecraft ever landed softly on an asteroid o Itokawa: Japan undertook to send the spacecraft Hayabusa to this asteroid to take measurements, collect samples, and return them to Earth. Lost signal and then 3 months later it came back! o M-type asteroids: nicel0iron is an opaque material, returning only reflected light. These have flat spectrums and a moderate albedo of about 10% o E-type asteroids: These have the highest albedo (40%) and e stands for enstatite (a mineral) o S-type asteroids: about 16% are chondrites and the rest achondrites. These are confined to the inner belt. o Wonderful Vesta o Most thoroughly observed asteroid is the 4 Vesta, o One of the brightest in the sky and at times just visible to the unaided eye o Observations show a general covering of eucrite material (distinctive type of basalt flow) an irregular area of diogenite material (a non-volcanic igneous rock formed within the body) and a roughly circular area with a combination of diogenite material and an adjacent olivine-rich area o Was struck several times in history, large impact craters mark its equator o One crater covers 75% of it o Spacecraft Dawn was sent by NASAto learn more Chapter 13: Meteorites o Definitions o Falls: a meteorite whose entry through the atmosphere has been witnessed, and someone has recovered a piece (or all) or the object o Finds: a meteorite you more or less stumbled across and have no information of when it got there o Classification o Least sophisticated classification = irons, stones and stony-irons o Stones or aerolites: almost entirely a non-metallic silicate/oxide material; subdivided into chondrites and achondrites  Chondrites and chondrules: these have never been altered greatly since first compressed together. Chondrites have chondrules which refer to the small rounded inclusions in them; poorly blended aggregates of different materials. Chondrules are thought to condense from a hot 7 cloud of gas and dust, very early in the Solar System history, by a ‘flash-melting’of dust aggregates in the solar nebula  Achondrites: igneous rocks that have been at least partially melted and recrystallized. These are fragments of products of crystallization from a magma. If the fragment is a chunk of the residual product it is called a primitive achondrite • When molten rock crystallizes to a solid, we call it some type of igneous rock. The material left behind that didn’t melt is called a residual rock.  Carbonaceous matter: some meteorites contain carbonaceous material. The carbonaceous chondrites contain a few percent of carbon and some of them exhibit a large variety of organic compunds. External delivery of organic material is now widely accepted as an alternative or additional pathway to the internal production of such material on the early Earth and it may have contributed to the start of life (“building blocks”)  Accretion: the process of clumping together of the various products appearing in chondrites; very important process o Stony-irons or siderolites: a nearly mix of 50/50 iron + nickel metal alloys and non-metallic silicate/oxide material o Irons or soderites: almost entirely iron + nickel alloys o Chondrules o Learn how they likely formed and what they represent o Interaction with Earth’s atmosphere o Meteors o Dust to sand size o There must be a source of interplanetary dust particles to replace those that are continuously being lost. There are 2 possible sources:  1) asteroids—the asteroid belt between Mars and Jupiter has many collisions and when the asteroids break into smaller pieces, which in turn collide, they create even smaller bodies. This continual fragmentation of asteroids creates micron-sized and larger chunks  2) comets—they trail dusty tails as they rush toward Sun, and most comet orbits take these icy bodies far outside the plane of the Solar System o Meteor showers associated with comet tails o Showers of meteors come from very specific regions of the sky and travel together in space in the same direction along with a common orbit. They strike Earth’s atmosphere at nearly the same position along Earth’s orbit, and consequently we see their meteor trails each year against the same background of stars. o Temple-Tuttle did a pass that left so much dust behind it’s referred to as the “Great Leonids Shower” o Leonid Shower  Nov. 16-17  Hourly count: variable  Velocity: 42.4 miles/sec  Associated comet: Tempel-Tuttle o Fireballs o Produced by large chunks of rock and iron that were knocked off asteroid parent bodies by collisions o Particles in an average meteor shower never survive to reach Earth’s surface, but most meteoroids that produce fireballs are massive enough to survive atmospheric passage, often explosively disintegrating into several smaller pieces en-route o The light is usually visible over a wide area, and the sound can commonly be heard over 50 km o Generated by two distinctly different mechanisms: the burning of the solid body itself and the incandescence of the atmosphere immediately around the burning mass 8 o When it reaches a temp more than 1650 degrees C, material begins to slough off as the rock surface literally liquefies and almost immediately, the ablated material vapourizes (ablation=erosion process by removing small masses) o Kinetic energy equation o KE= ½ MV 2 o The important thing to notice about the kinetic energy equation is that it varies with the square of its velocity but only with the first power of the mass o The higher its kinetic energy when it meets the upper atmosphere, the higher the atmospheric drag on the meteoroid and the more rapidly it heats up, as atmospheric resistance acts to convert this energy of motion to heat, light and sound o Kinetic energy: a moving mass has energy associated with its motion o Inertia: a body’s resistance to a change in its motion o Momentum: a product of the body’s mass, the amount of material it contains, and its speed or velocity. The force required to change its motion—the speed it up or slow it down or change its direction depends on this. o Regmaglypts: surfaces of some meteorites are marked with these depressions resembling thumbprints that form by ablation o Fusion crusts: Alayer of glass (commonly dark or black in colour) caused by melting. o Principal tools of investigation o Petrographic microscope: to look inside any rock or meteorite (must be a very thin slice of the rock on a glass side) o Electron microphobe: used to chemically analyze rocks which uses a tiny beam of electrons to impact micron-sized volumes of the sample and tell us what elements are present in that volume and in what proportions o Mass spectrometer: measures the amounts of very selective radioactive isotopes in the sample and from that we can tell how old the sample is Unit 5 Introduction o What defines a gas/ice giant? a large, massive, low-density planet composed primarily of hydrogen, helium, methane, and ammonia in either gaseous or liquid state o 4 in the solar system: Jupiter, Saturn, Uranus, Neptune o Some of their common features  Atmospheres of hydrogen and less helium  Very hot cores  Cores that are sometimes called rocky but are a mix of heavy elements in a solid state  Surrounded by systems of rings and natural satellites  Rotate rapidly, resulting in strong atmospheric winds o Origin in the solar system o Astronomers announced that they figured all gas giants – even the four in our solar system – were either formed within the first 10 million years of the development of a star-planet system or they didn’t ever develop. o The idea is that all those volatile and liquid elements that would be given off by an early star would gather quickly into frozen blobs in the cold outer reaches of the system; there, they would grow and their gravitational attraction would increase rapidly – and they’d start pulling greater and greater quantities of volatiles and liquids into themselves. o Inevitably, the larger masses would start interfering with the orbits of the slightly smaller masses, and the combined gravitational/rotational interactions would have the effect of flinging the smaller ones either out to the margins of the planetary system or in toward the central star. 9 o Collision of Shoemaker-Levy 9 with Jupiter o Because of its strong gravitational force, Jupiter probably gets hit by comets more often than most planets o In 1994 fragments from a disrupted comet smashed into Jupiter (Shoemaker-Levy 9) and was pulled into at least 21 pieces that looped out away from Jupiter in long elliptical orbits o Produced fireballs o We can use this event in two ways  Better understanding of the nature of Jupiter’s atmosphere: Astronomers used the impacts as probes of Jupiter’s atmosphere. They were able to fine-tune their models of Jupiter to better represent the atmosphere  Planets are hit by large objects such as asteroids and the heads of comets: we now recognize that pattern as the scar of a comet impact Chapter 14: Jupiter o General planetary properties o Distance from sun: 5.3 AU o Diameter a bit over 11 times Earth’s diameter o Normally the 4 brightest object in the sky o 3 times larger than Saturn (next planet) and 318 times Earth’s mass o Density: 1.326 g/cc o Fast rotation
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