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Transcript
See Q. “Sampler” on packet, pages 12-15 1st Lecture Exam on Tuesday, October 2nd (Multiple Choice) EVOLUTION OF THE UNIVERSE: GALAXIES - Milky Way o Democritus (450-370 BC) gave the first notion of the milky way o Galileo (1610 BC) ! First to really develop the telescope ! First to really look at space and the milky way o Georges Lemaitre (1927) ! Came up with the idea of the big bang o 20-15 BYA: Big Bang o EP Hubble (1924) ! Looked at the milky way and discovered that there were billions of galaxies beyond the MW o G. Gamow (1940s) ! Looked into the evolution of protogalaxies o Expansion: atomic fusion & cooling o Gravitational attraction = galaxies formed - Solar System o Nebular Theory [Pierre Simon Marquis de LaPlace (1815)] ! Matter became clustered in stars with the outer eddies condensed in chunks ! A hypothesis concerning the origin of the solar system according to which a rotating nebula cooled and contracted, throwing off rings of matter that contracted into the planets and their moons, while the great mass of the condensing nebula became the sun. - Earth o Earth is about 4.6 billion years old o All planets circle sun in same direction and their orbits lie on the ecliptic plane o Earth’s formation: ! Planetesimal (chunks of matter) accretion by coalescence ! Internal melting due to • Gravitational compression • Impact heating • Radioactive decay ! Differentiation into layers • Light material rises to the top (surface) • Heavy material sinks to the center (core) ! 4.2 to 3.7 billion years ago, crustal cooling & thickening start and continued until 1,000 million years ago, when crustal plates break up & begin migrating, initial mechanisms of plate tectonics • Sea-floor spreading • Subduction • SIMA: magnesium silicates o Crust under mountains are thicker than any other areas (called mountain roots, allows crust of the continents to extend deeper through the mantle) Rocks Formation, Classification, and Relationships • Pockets of magma approach surface and cool -> Igneous o Weathering: process of breaking down rocks o Transportation: moves downhill usually and clumps up • Sediments stack up and the bottom layers become compacted from high pressure (lithification) -> Sedimentary • Heat and pressure create Metamorphic o Deformed rocks from some previous cycle (magma) o Melting allow the process to start over Rock Formation • +/- 100 elements -> 2000+ minerals -> combine to form rocks o Physical properties o Chemical properties o Origin, processes formation Rock Genesis • 3 basic groups and 6 sub groups • Igneous (Intrusive aka plutonic or extrusive aka volcanic) • Sedimentary (Detrital aka clastic or chemical) • Metamorphic (foliated or non foliated) Definitions • Intrusive (igneous): form inside the crust of the earth = plutonic • Extrusive (igneous): form on surface of earth = volcanic • Detrital: chunks of rock from weathering and breaking down that clump up eventually • Chemical: non chunks • Foliated: cleavage, parallel lines Igneous Rocks • Crystalline structure (even during cooling and solidification) • Location (internal/external) • Temperature (cooling rate) • Speed of formation • Size of crystals -> strength • Igneous intrusive rock (plutons, a lot of plutons = batholith) • Dike: vertical structure • Sill: horizontal structure - Burial causes compaction - Pressure solution along grain contacts - Deposition of dissolved materials in percolating water and grain residues Two possible components: 1) Rock Particles (grains) 2) Intergranular cement (also called matrix) *Their strength and other properties may be different from one another and may affect further weathering, infiltration, water storage, etc. Two Sedimentary Rock Types: 1) Detrital (aka Clastic): with rock fragments/grains and cement 2) Chemical: with soluble materials - These may be precipitated by inorganic or organic (biological) processes - Organic example: Coral limestone, coal Detrital Inorganic Chemical Organic Sedimentary METAMORPHIC ROCKS - Metamorphic rocks have been subjected to processes of metamorphism (e.g. heat, pressure, chemical fluids) • Contact metamorphism: in close proximity to magma masses, lots of heat • Regional metamorphism: occurs over extensive areas, especially along subduction zones • Hydrothermal metamorphism (least common): contact with thermal waters *For diagrams of the forms of metamorphism, see textbook - Metamorphic rocks are also divided by INTENSITY of metamorphism processes • Low grade metamorphism (minimal alternation) • High grade metamorphism (significant change) Metamorphic Rocks 1. Metamorphic rocks are classified by Presence of Foliation • Foliation - Cleavage Plains • Foliated - Mineral crystals are visibly aligned, rock displays a banded aspect (2+ minerals must be present.) 1. Mainly produced by Compressive Stress • Non-foliated - Rocks have one single mineral, and/or have minimal deformation (lowgrade), and minerals have equidemensional crystals (i.e.+- equal dimensions. 2. Metamorphism Results in Specific Types of Rock (know this) - Water is attracted to mineral particles; these have negatively charged particles - Water molecules also attach to other water molecules - Many water layers attach on mineral particles - Water layers act like wedges, pushing apart mineral particles. Minerals in rocks are altered and weathered o Expansion when wet, contraction when dry • Hydrolysis - Water molecule splits into 2 ions - H2O = HO + H - These ions then combine with minerals - Occurs more frequently at high temperatures • Oxidation and Reduction - Minerals react in the presence or absence of oxygen - Oxidation: occurs in aerobic (O-rich) environments o Produces red/yellow/orange colors - Reduction: occurs in anaerobic (O-deficient) zones o Produces gray/dark brown/black colors • Weathering is needed for the development of different sediments and soils • Main elements in Earth’s crust o Oxygen (O) o Silicon (Si) o Aluminum (Al) o Calcium (Ca) o Magnesium (Mg) o Sodium (Na) o Potassium (K) o Iron (Fe) (SiAlOCaFeKNaMg) - Order of relief: difference of elevation o First-Order landforms ! Oceans and landscapes o Second-Order landforms ! Features: Major oceans or continent subdivisions ! Examples: mountain ranges, large river valleys, deltas, ocean basins, marine fans ! Second order includes third order o Third-Order landforms ! Examples: mountains, glaciers, domes, streams o Fourth-Order landforms ! Miniature relief: an area with Tafoni, a rock Pedestal, a group of exfoliated blocks *Orders of relief includes one another (fourth falls in third, which falls in second…) * 1st and 2nd order landforms (continents, oceans) are caused by global dymanics (plate tectonics) over long time periods * 3rd and 4th order landforms caused by erosion and deposition of materials over shorter time periods