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Earth Science

Lecture 1 Scientific Method 1. Hypotheses 1. Recognizing the problem 2. Prediction 2. Collecting data 3. Test 3. Proposing hypotheses 4. Accept or reject hypotheses 4. Testing hypotheses - A sequence of steps for systemically analyzing scientific problems in a way that leads to verifiable results 1. The earth’s outer core is liquid 2. Seismic waves should transit differently though different layers 3. Wait for an earthquake to occur 4. Seismic waves are unable to transmit through liquid so accept the hypotheses Lecture 2 Formation of the Universe, Solar System, and Earth Six stages of PPD formation 1. HII (hydrogen 2 region) – hot, intense, advance shocks 2. When pushed, induce memento, and clouds start mixing itself 3. Ionization front passes cloud, induce a lot of motion which collapses the cloud 4. Core keeps getting blasted by UV radiation, and cloud is evaporated, and because of gravitational forces a star forms 5. Left with dense core, called a proplyd 6. YSO- young stellar object, can still dump isotates, the star in the centre heats the disc by radiation, 150 million kilometers  1 AU POTENTIAL QUESTION Different mineral sequence? 1 – calcium aluminum oxides Intermediate – calcium aluminum magnesium silicates Last – iron, nickel, metal, sodium, calcium, magnesium Birth of the first stars The graviatation pull of a more massive region of a nebula began to suck in surrounding gas, and it grew in mass, and therefore density. As this dense region attracted more gas the gas compacted into a smaller region, and the swirling movement of gas transformed into a rotation around an axis. As the gas continued to move inward in to a smaller volume the rotation rate became faster. Because of the increased rotation the nebula evolves into a disk shape and as more matter rains onto the disk, it continues to grow until gravity collapses the inner portion of the disk into a dense ball. As the gas crams into a smaller and smaller space, the temperature increases and the central ball of the disc becomes hot enough to glow (becomes protostar). It continues to grow by pulling in successively more mass, until its becomes extremely dense and ints temperature reaches 10 million degrees. Solar System PPD - source of planets, contained all 92 elements, the disc from which our SS formed Terrestrial Planets (inner planets) - like earth, they consist of a shell of rock surrounding a ball of metallic iron alloy - Mercury, Venus, Earth, and Mars Gas-giant Planets/Jovian Planets (outer planets) - most of their mass consists of gas and ice - Jupiter, Saturn, Uranus, Neptune Crust - consists of variety of rocks, 0.5% of the Earths radius, depth is 10-70 km Mantle - largest part of the Earth, consists of an ultramafic rock called peridotite, 67% of the Earths radius, 2880km thick layer surrounding the core Outer Core - consists of liquid iron alloy, temperature is very high, irons flow generates Earth’s magnetic field, 30.8% of the Earths radius, 2260km Inner Core - solid iron-nickel alloy that may reach a temperature of over 4,700 degrees, hotter than outer core, solid because deeper and is subjected to greater pressure, rotates faster than the rest of the Earth, 1.7% of the Earths radius, 1220km Going from PPD to Planetesimals - disk of gas and dust spinning around young Sun, dust grains clump into Planetesimals, Planetesimals collide and collect into planets Types of Meteorites - Stony; chondrites, achondrites (largest group, formed part of the outer crust of a planet, some contain chondrules and can pre-date the formation of our planet and the SS, oldest known matter to use for study) - Stony-Irons; pallasites, mesosiderites (compromised of nickel-iron and stone, formed at the core/mantle boundary of their parent bodies) - Irons; magmatic, non-magmatic (once part of the core of a vanished planet, densest materials among earth) Pluto Situation - Until 2005 Pluto was considered to be a planet, but it did not fit the modern definition of a planet so it had been dropped... 1. Orbits around the sun (orbit lies outside of Neptune’s) 2. Enough self-gravity to pull itself into a spherical shape 3. Has cleared the neighborhood of its orbit Forming the Planets and the Earth-Moon System 1. Nebula forms from hydrogen and helium left over from the big bang, as well from heavier elements that were produced by fusion reactions in stars or during explosions of stars 2. Gravity pulls gas and dust inward to form an accretion of disk, and a glowing ball, the proto sun forms at the center of the disk 3. Dust concentrates in the inner rings while ice concentrates in the outer. The dense ball of gas at the center of the disk becomes hot enough for fusion reactions to begin and when it ignites it becomes the sun 4. Dust and ice particles collide and stick together forming Planetesimals 5. Forming planets from Planetesimals: Planetesimals grow by continuous collisions, and an irregular shaped proto earth develops, interior heats up and becomes soft 6. Gravity reshapes the proto-Earth into a sphere, and the interior of the Earth differentiates into a core and mantle 7. Soon after Earth forms, a small planet collides with it, blasting debris that forms a ring around the Earth 8. The moon forms from the ring of debris 9. The atmosphere develops from volcanic gases, when the Earth becomes cool enough; moisture condenses and rains to create the oceans. Some gases may be added by passing comets Lecture 3 Geologic Time Relative Age - geological time that places events ordered by relativity Absolute Age - geological times that places events ordered by numbers age Cross Cutting Relationships - a geological feature cuts across another the feature that has been cut is older (igneous dike cuts across a sequence of sedimentary beds, so the beds must be older than the dikes Inclusions/Xenoliths - any piece of rock included in another rock must be older than the rock in which it is incorporated (if a layer of sediment deposited on an igneous layer includes pebbles of the igneous rock, then the sedimentary layer must be younger) Superposition - oldest layer is at the bottom and the youngest layer is at the top in a sequence (1 oldest, 2, 3, 4 youngest) Unconformities - an unconformity is a rock interface which represents a gap in the geological record like pages missing in a book, example would be the Grand Canyon since it separates rocks of Precambrian age from later flat-lying Paleozoic rocks Original horizontally - sedimentary layers and lava flows are usually deposited horizontally Baked Contacts - an igneous intrusion bakes surrounding rocks, the rock that has been baked must be older than the intrusion Fossil Succession - principle that the assemblage of fossil species in a given sequence of sedimentary strata differs from that found in older sequences or in younger sequences, species appears at a certain level then goes extinct at a higher level - can define relative ages with this principle ex. If we find a bed containing Fossil A, we can say that the bed is older than a bed containing Fossil F. Fossil species occur in a predictable order Age of the Earth - relative age of the earth is 4.52-4.56, Chondrules are the second oldest solar system solids, and Ca, Al- rich inclusions are the oldest and first solar system solids Acasta Gneiss - oldest dated rocks on Earth Major Boundaries 1. Precambrian: 4.6 Ga to 542 Ma 2. Paleozoic: 542 Ma to 251 Ma 3. Mesozoic: 251 Ma to 65 Ma 4. Cenozoic: 65 Ma to Present Lecture 4 Earth History Hadean Eon - time interval between the birth of Earth, and 3.80 Ga as the Hadean Eon because during this interval the Earth’s surface was at times an inferno Archean Eon - had started about 3.8 Ga (billion years ago) - volume of continental crust increased, rocks formed at both subduction zones and at hot-spot volcanoes, collisions sutured volcanic arcs and hot spot volcanoes together creating progressively larger blocks called protocontinents, and as time passed protocontinents became cooler and stronger and between 3.2 and 2.7 Ga the first cratons, of durable continental crust had developed. - First continents and first life appeared during the Archean Eon (chemical molecular fossils, isotopes signatures, fossil forms) Lecture 5 Tectonics I Continental Crust vs. Oceanic Crust - continental crust is 35km thick, and has a relatively low density - oceanic crust is 10 km thick, and has a higher density Lithosphere vs. Asthenosphere - lithosphere (crust, uppermost mantle) is about 100-250km thick, and is relatively rigid while the asthenosphere (upper mantle) is about 200km thick, and is relatively ductile meaning easily deformed Basic Tectonic Model - Lithosphere is thin, cool and hard, and the Asthenosphere is ductile and hot - Lithosphere is broken into large fragments called plates, and plates “float” on the asthe
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