Planet Earth post midterm
Planet Earth post midterm Geol 105
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This 12 page Class Notes was uploaded by Abi Sommers on Friday October 7, 2016. The Class Notes belongs to Geol 105 at 1 MDSS-SGSLM-Langley AFB Advanced Education in General Dentistry 12 Months taught by John Platt in Fall 2016. Since its upload, it has received 57 views.
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Date Created: 10/07/16
9/30 Rock Deformation : - Rock Fractures - tensile fractures open out - shear fractures slip along the fracture surface - natural faults are a type of shear fracture Structures in zones of continental rifting Normal fault: the top side slips down relative to the bottom side - A normal fault occurs when the crust is extended Hanging wall has moved down relative to the footwall - ▯ - Graben structure: - A valley which is defined by two normal faults (horsts), inclined in opposite directions. ▯ Structures in zones of plate convergence : - Tibet, area of shortening and thickening of continental crust - 3 Reverse fault: the top side slips up, relative to the bottom side ▯ A thrust is a low-angle reverse fault - Glarus Thrust, Central Alps Transform zones - Strike-slip faults, slip horizontally parallel to fault surface - San Andreas fault - Right-slip fault, when crossing the fault, have to go down to your right to find the fault ---------------------------------------------------------------------------------------------------------------------------- Week 7 : 10/3 Rock Deformation II cont’d Retaining and releasing bends - A bend to the right on a right-slip fault is a releasing bend, this may produce a basin - A bend to the left on a right-slip fault is a restraining bend, this may produce uplift and mountains ( example : Salton sea pull-apart basin along San Andreas Fault) - San Andreas fault unique because of its “Big Bend” - Restraining bends cause overlap of the crust, creating mountains Tectonic associations of faults: Summary: - Normal faults are most common in right zones - Thrust faults are common in zones of plate convergence - Strike-slip faults are dominant in transform zones Fault Rocks: - Faults contain zones a few mm to a km wide of fault rock - Fault rocks are produced by mechanical and chemical breakdown of the rocks on either side of the fault - Fault breccia: produced by mechanical fragmentation dominant ▯ - Fault gouge: chemical alteration to clay▯ - Mylonite : Ductile deformation ▯ Folds: - Bedded strata may be tilted and folded by forces associated with plate motion • Attitude of bedding – strike and dip Strike and dip - The strike is the orientation of the horizontal line in the plane of bedding - The dip is the inclination of the bedding from the horizontal - The direction of dip is perpendicular to the strike and must be specific ▯ - An anticline is afold that closes upwards - The oldest rocks are in the core of the fold▯ - A syncline is a fold that closes downwards - The youngest rocks are in the core of the fold ▯ Structures and maps : - A geological map is a direct representation of the geology seen on the Earth’s surface ▯ 10/5 Origin of the Earth and the Solar System: Stages in the formation of the solar system: 1. Formation of solar nebula and protostar 2. Accretion of planetesimals 3. Formation of planets - Processes started 4560 million years ago, and took a few tens of millions of years to complete. Eagle Nebula : - Cloud of gas and dust like these are the birthplace of stars ▯ - very big and dilute - Would not be able to distinguish space from a vacuum - Visible through telescope - “Black yama” - Suppression of gas and dust creates Eagle Nebula, starts to contract under its own gravity and start a new star or several - gravitational collapse is first step of creating a star . 1 Collapsing cloud - a diffuse, roughly spherical, slowly rotating nebula begins to contract - As contact, start to spin, “concentration of angular momentum” (like a figure skater) ▯ - gas clouds contracting hundreds to thousands of times - centrifugal force, shorthand way of expressing when something rotates, in order to keep it together have to pull in ( flying away from the force) 2. Formation of solar nebula - Stars and planetary systems form by collapse of interstellar clouds under gravity - Clouds collapse into a disk - central part of disk collapses to form a protostar - hot, fairly high density ball of gas in the middle ▯ . 3 Accretion of planetesimals - planetesimals- little, proto planets - grands of rock dust, minerals and ices accreted to form km-sized bodies - gas getting more concentrated as result of collapse of the cloud - first, form dirty snow. Bits of dust and ice stick to each other - dirty snow flakes turn into dirty snowballs, they grow bigger until becoming big enough to regard as celestial object - Planetesimal. . 4 Formation of planets - start of nuclear fusion in proto-star generates solar wind- strips gas from inner solar system - planetesimals accrete to form terrestrial planets in the inner solar system - gas giants grow around larger planetesimals in outer solar system - * know about inner planets- Venus, Earth, Mercury, Mars * outer planets - Jupiter, Saturn, Uranus, Neptune, Pluto - asteroid belt between jupiter and inner planets - Jupiter’s gravity stops asteroid belt substances from becoming planets - collisions of planetesimals form creations of planets - larger objects pull in more and more material, gas, and planetesimals -while planets were developing, sun developed from a proto-star. - nuclear fusion produces massive amounts of energy - gas in outer part of the solar system was able to form the gas giants ^one big problem with this theory of creation of planets - most gas giant planets found around other stars are very close to their parent stars Terrestrial (rocky) planets - Mercury, Venus, Earth- Moon System - Venus - Earth-Moon system - Mars - Several of the moons of Jupiter and Saturn and some of the asteroids are comparable in size composition and structure to the terrestrial planets Venus : - Sister planet , remarkably similar in size and composition to Earth - Very weak magnetic field - No plate tectonics - Curious why different from Earth in this way - Extensive volcanic activity ( but no plate tectonic so mostly mantle plume, more vigorous convection in the mantle) - Cryptic tectonic structures - “arachnoid” because looks like spider webb ▯ - Very thick, hot atmosphere - No oceans ( completely dry) Landforms on Venus - Tesserae▯ - Corona ▯ - Do not know how these things were formed Mars : - About half the diameter of Earth - No magnetic field- solid core? - No plate tectonics - Active volcanic and tectonic activity during first billion years - Mantle plumes probably most common volcanic process on the planets - Very thin, cold atmosphere - No surface water, but there may have been in the past - Some features look like once frozen glaciers - Alluvial channels on Mars look like once stream channels - Valle Marineris : 5 km deep , largest feature on mars, many times deeper than the Grand Canyon - ▯ Saturn : - Titan is Saturn’s biggest moon - Saturn’s rings massive compared to its rings, but Titan could be responsible for movement of the rings - Titan - Larger than the planet Mercury - Rocky core, water mantle, thick ice crust - Nitrogen atmosphere - Lakes of methane, rains methane, snows methane 10/7 The Early Earth: Origin of the Earth-Moon system - Earth’s moon unique in that it is a significant fraction of the size of the Earth - Composition of the Moon is very similar to the Earth’s mantle - Theories for the origin of the Moon - Capture - Moon was formed as separate, mini planet and captured by the orbit of the Earth - Fission - Moon formed out of part of the Earth and thrust into space - Formation together w/ the Earth in the same orbit - Formed together as separate objects in the same orbit from the start - Interplanetary collision - Formed out of interplanetary catastrophe ^ most of these not possible or improbable. - Capture : not possible unless two objects touch each other - Fissure: no way Earth could spin so rapidly to throw the moon off. - Formation W/ Earth: possible, but then why is the moon so much larger comparison to the Earth compared to other planets and their moons. - Interplanetary Collision: Most likely - Mars sized body impacted Earth - giant impact propelled shower of debris into space - Earth reformed as largely as molten body and moon aggregated from debris - impact sped up Earth’s rotation and tilted Earth’s orbital plane 23 degrees. - Moon pushed further and further away by time and forces - Moon/ Earth 1:81 Titan/Jupiter 1:20,000 (<-- Size) - Composition of the moon very similar of composition of Earth’s mantle - Moon does not have core, ball of rock, close relationship to the Earth - Moon always presents the same face to the Earth, always seen the same side of the moon ( before Apollo, had never seen backside of the moon) The First Crust: - After formation of the moon, the Earth’s mantle may have been largely molten - An early crust may have formed on magma ocean, made of anorthosite: not now preserved (composed almost entirely of plagioclase) - Early anorthosite crust on the moon still there: 4.5 billion years old - Earth’s early crust was continuously destroyed and recycled by mantle convection and asteroid impacts - Earth’s moon a clue to the nature of the early Earth: - The lunar highlands are made of anorthosite - Lunar mare are floored by basalt - Lunar surface is dominated by impacts - Euler crater: probably formed as result of relatively small object. When impacting body hits surface of a planet, hits and evaporates, instantly creating crater - Central Peak, after hugs mass of hot material is ejected leaves central peak. ▯ - Mare Orientalis: a multi-ring impact basin ( on other side of the moon) - Result of bringing sizable object in and hits the moon, produces 700 km crater. Rings are effects of progressive collapse into lunar hole ( a few hundred kilometers deep) - Mare are themselves impact basins ▯ - Lunar “seas” were formed as giant impact structures before 3.9 Ga (gigayears), later filled by flood basalt. Similar impacts must have occurred on Earth. - Because Earth so close to moon during all this violent collision, impact events. - Many early impactors may have been comets, which supplied Earth with water and organic compound; may be formed Earth’s oceans and atmosphere ▯ The Early Earth: - Heavy Bombardment by asteroids and comets during first few hundred million years - Rapid convective overturn of mantle continuously recycled the primitive crust - Early was 20% less bright than at present ( meaning ice age) - Early atmosphere rich in N2, C02, Possibly CH4 - Early oceans hot, acidic - No life, and hence no oxygen - Oxygen almost 100% due to photosynthesis ▯ - Remember Eons and Sequence by which they occur Hadean Eon: - 4560-3900 Ma: Origin of Earth to first preserved crustal rocks - Heavy bombardment by asteroids and comets during first few hundred million years - Rapid convective overturn of mantle - Early sun 20% less bright - Atmosphere rich in N2, C02, CH4 - Early oceans hot, acidic - No Oxygen
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