EXAM 3 EARTH SCIENCE - Day 24: Geologic Cycle Geologic Time...

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Day 24: Geologic Cycle Geologic Time Scale * Major Divisions: 1. eons : based on evidence of life in the geologic record (Precambrian, Phanerozoic) 2. eras : based on major worldwide changes in life forms; major extinctions Paleozoic: "age of fishes" Mesozoic: "age of reptiles" Cenozoic: "age of mammals 3. periods : based on lesser changes in life forms Geologic Cycle * all endogenic and exogenic processes that cause changes in the Earth's lithosphere * consists of the following cycles: 1. hydrologic cycle 2. rock cycle 3. tectonic cycle Rock Cycle * formation and transformation of the materials that comprise the Earth's lithosphere * mineral : naturally-occurring, inorganic solid, possessing a specific chemistry and a specific atomic structure ---silicates : minerals containing silicon and oxygen; most abundant group of minerals at the Earth's surface ---polymorphs : minerals having the same chemistry, but different properties (ex. diamond and graphite) * rock : aggregate of minerals * The rock cycle describes how different classes of rocks form and change (igneous ---- sedimentary ---- metamorphic) Igneous Rocks * rocks formed via cooling and solidification of molten rock * molten rock originates deep within the Earth's interior due to radioactive decay and friction * 2 divisions: 1. intrusive ("plutonic"): igneous rocks formed below the surface = within the Earth's interior, molten rock is insulated by the surrounding rock, resulting in slow cooling = slow cooling allows for large mineral crystals to form in the solidifying rock mass = intrusive rocks have coarse-grained textures (ex. granite) 2. extrusive ("volcanic"): igneous rocks that form at the surface = extrusive rocks form from rapid cooling/solidification of molten rock = rapid cooling does not allow time for large mineral crystals to form = typical textures are glassy, vesicular and fine-grained (ex. Basalt)
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Day 25: Rock Cycle (continued) Igneous Rocks (continued) * magma : molten rock existing beneath the surface; contains abundance of dissolved gases; formation of intrusive igneous rocks * lava : molten rock existing on the surface; lower content of dissolved gases; formation of extrusive igneous rocks * classifications based on chemistry: 1. felsic : rich in silicon and oxygen; light-colored; low-density 2. mafic : rich in iron and magnesium; dark-colored; high-density Sedimentary Rocks * rocks that form via lithification of sediments and/or organic materials * lithification : compaction, cementation, and hardening of sediments to form solid rock * processes of weathering and erosion wear down the rocks and organics at the surface to form sediments * most abundant rocks at the surface * sedimentary rocks are the least resistant to weathering and erosion * fossils and fossil fuels are generally found in sedimentary rock structures. (exception:
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EXAM 3 EARTH SCIENCE - Day 24: Geologic Cycle Geologic Time...

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