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Transcript
A Dynamic System View from Apollo What can you make out? It’s our Biome! Nature’s splendor How old is old? The oldest meteorites and moon rocks found on earth are 4.6 billion years old. The oldest earth rocks found are zircon grains from a sandstone in western Australia, dated 4.1 - 4.2 billion years old. What happened on Earth during this long period of time? Many natural events: Meteorite impacts Volcanic eruptions & lava flows Mountain building Earthquakes Erosion Slow movement of continents Formation and destruction of ocean basins Glaciations Climatic changes All of these natural events are still going on today Some events that occurred in the past, and left a record in the rocks, ARE NOT OCCURRING TODAY, or haven’t occurred in the span of human existence: Huge meteorite impacts Large glacial ice sheets Other events occur so slowly that they are difficult to measure: Plate tectonics: sea floor spreading; continental drift Erosion of mountain ranges Still other events are short lived but very catastrophic: Volcanic eruptions Earthquakes Floods Landslides, mudflows, avalanches, etc. Layers of the Earth The Earth is divided into 3 basic layers Crust (composed of…) O and Si Mantle (composed of…) Fe and Mg Core (composed of…) Fe and Ni very hot The Crust Continental crust About 35 km thick; 60 km thick in mountain ranges Granitic composition (granite rock, basic) Oceanic crust About 5 – 12 km thick Thin layer of unconsolidated sediment covers layered igneous rock Layered structure Pillow basalts (basaltic rock that erupted below water) “sheeted dikes” (interconnected basaltic ridges) Gabbro (course grained equivalent of basalt, which cooled slowly) The Mantle Lithosphere = the outer mantle + the crust Asthenosphere = the inner mantle Roughly the outermost 100 km of Earth Divided into tectonic or lithospheric plates that cover the surface of the Earth Depth of 100 – 250 km Seismic wave velocity decreases (less dense) Rocks at or near melting point Plastic behavior; solids that flow (magmas) Convection in this layer moves the tectonic plates The lithospheric plates “ride” on the convection currents of the asthenosphere The Core Outer core Molten iron, Fe, (85%) with some nickel, Ni Inner core Solid iron (85%) with some nickel Also contains lighter elements such as silicon (Si), sulfur (S), carbon (C), &/or oxygen (O) Rocks vs. Minerals What are rocks? Aggregates of one or more minerals What are minerals? Naturally occurring Inorganic Solids Definite chemical composition Characteristic internal crystal structure How Do Rocks Form? By cooling, hardening, and crystallizing from hot, molten lava By the alteration of pre-existing igneous or sedimentary rocks by heat and pressure = Sedimentary rocks (terrigenous, clastic, or detrital) By forming from the precipitation of dissolved chemicals in water = Metamorphic rocks By forming from the compaction and cementation of sediments = Igneous rocks Sedimentary rocks (chemical and biochemical) By forming from accumulated organic matter Sedimentary rocks (organic; e.g. coal) THE ROCK CYCLE Rocks are constantly “on the move” and cycling throughout the Earth Just like T-rex walked on but they have broken down and reformed time and time again Ripples in beach sand, such as those in the upper photograph (A) may someday become a rock like the sandstone in the lower photograph (B). This sandstone was part of a beach over 200 million years ago in the Triassic period. Breccia & Sandstone with fossil (remains & imprints) Igneous Rocks – sometimes referred to as “fire rocks” Granite, Pumice, & Obsidian Rocks - which are these samples? intrusive or extrusive? foliated vs. non-foliated metamorphic rocks - gneiss, marble, & slate illustrated Fundamental Principles of Geology Most sedimentary rocks occur in the form of layers called beds or strata. Each layer is the result of the deposition of sediment during some natural event. Principle of Superposition Principle of Original Horizontality Oldest rocks are on the bottom Younger rocks are on the top Sediments are deposited in flat layers Principle of Original Lateral Continuity Sediments are deposited over a large area in a continuous sheet Other types of Unconformity 1) Angular unconformities Implies tectonic deformation and erosion of underlying strata. Grand Canyon, Arizona Other types of Unconformity Nonconformity Sedimentary strata overlying igneous or metamorphic rocks (in an erosional - not intrusive- contact) Grand Canyon, Arizona Other types of Unconformity Disconformity An irregular surface of erosion betwen two units of parallel strata. Death Valley, California Other types of Unconformity Paraconformity A planar surface between two parallel units of sedimentary rock, representing a period of nondeposition, but no erosion. Grand Canyon, Arizona