GEOL 101 Exam 1 Study Guide Lecture1 Geology the study of the Earth its history composition surface and structure The Geological record is the information that can be uncovered by looking at rocks The earth is made up of 4 major layers The Mantle A viscous solid layer of the earth that comprises about 67 of the earth s mass The Crust The low density outer portion of the earth Its low density allows it to float on the mantle The continental portions are about 40 km thick and the ocean portion Is about 7km thick Comprises less than 1 of Earths mass Liquid Outer core Dense liquid portion of the earth comprising about 30 of Earth s mass Comprised of mostly iron Solid inner core Solid Iron sphere at the center of the earth About 2 of Earths mass The reason that solid rock can be viscous is that rock is strong over the short term but Weak over the long term hence it flows to support the shifting weight of continent The earth s major systems all interact with each other to form the Earth system These are the climate system the plate tectonic system and the geodynamo system Lecture 2 Plate Tectonics The Unifying Theory Continental Drift Proposed by Alfred Wegner The idea that large Scale movements of the plates in the Lithosphere cause the topographical Features of the Earth discovered because of the Geographical fit of the continents continents used to exist as a Supercontinent named pangea 250 Ma Seafloor Spreading Convection currents in the Mantle cause magma to rise and form new crust to appear at the Mid Ocean ridge Plates comprise the top layer of the Mantle Called the Lithosphere The Lithosphere slides over the weaker upper region of the Mantle called the Athenosphere Types of Plate boundaries Divergent plates move away from each other create new lithosphere ex Mid Ocean ridge Convergent move towards each other Oceanic lithosphere is recycled back into the mantle via Subduction Continental lithosphere is deformed when it collides with other plates Transform Plates slide past each other ex San Andreas Fault Lecture 3 Magnetism and Age determination The moving molten center of the earth creates Earth s Magnetic field When Magma crystalizes the magnetic minerals in it orient themselves in a direction consistent with the earth s magnetic field Over the earth s history this magnetic field reverses itself causing the rocks to alternates themselves in different magnetic orientations during different time periods These periods of different orientations are called magnetic chroms These chroms allow geologists to determine the ages of rocks This was vital in proving the theory of Seafloor Spreading The bands of reversed and normal chroms where discovered on the seafloor These bands are the same on each side of the divergent ocean boundary This showed that the oldest rocks in the sea are very young 200 Ma These rocks are recycled at convergent boundaries where Ocean is subducted under the Continental Crust Mantle Convection The driving force for Plate Tectonics is Mantle Convection The commonly accepted method for this engine is Whole mantle convection in which Convection currents occur throughout the entire mantle Hot spots occur where rises rapidly in a concentrated area this leads to Volcanic activity in the center of a plate such as the Hawaiian Islands Lecture 4 Earth Materials Mineral naturally occurring solid inorganic crystalline substance with a certain chemical composition most mineral structures are bonded via ionic bonding some are covalently bonded others are metallically bonded Crystallization is the process in which ions and atoms come together to for structures crystals can range in size depending on how much time they are given and how much room they have to form Formation Magma liquid rock cools crystalizes into a solid precipitate ions can come together in an aqueous solution to form crystals that precipitate out of the solution Classes of Crystals Silicates composed of silicon and oxygen in an anion that can join with many other cations of elements Most abundant form of minerals on earth Carbonates composed of Carbon and Oxygen in the anion CO32 in Combination with calcium and Magnesium Oxides Oxygen anion O22 and metallic cations Sulfides Sulfide anion S2 and metallic cations Sulfates Sulfate anion SO42 and metallic cations Properties Hardness measure how easy it is to scratch the surface of a mineral mohs scale of hardness 1 10 talc is the softest diamonds is the hardest Cleavage tendency of a crystal to split along a plane depends on crystal structure and bond strength Colour some minerals show a variety of colours Fracture tendency to break in irregular patterns Luster the way the surface of a miner reflects light Density Crystal habit the shape the crystals grow in Rocks solid collective of minerals Some have non mineral material in them such as organic material The rock Cycle is the cycle in which rocks transform from one of the three types of rocks Igneous Metamorphic Sedimentary Lecture 5 Igneous rocks Solids from melts Classification Texture formation Intrusive Magma crystalized slowly beneath the earth surface forming large crystals and a course texture formed by intrusions of magma into country rock Extrusive Magma crystalizes quickly on top of the earth s surface as a lava or as pyroclastic material fragments ejected from a volcano into the air fine grained with small crystals if pyroclastic it can have bubbles course texture Composition depends on minerals that make up the rock Felsic high silica content low in Fe and Mg Ex Granite and Rhyolite have the same felsic composition but they are different because granite is intrusive and rhyolite is extrusive Intermediate moderate Silica and Fe Mg Ex Diorite Andesite Intrusive Extrusive respectively Mafic low silicate high Mg and Fe Ex Gabbro Basalt Intrusive Extrusive respectively Ultramafic very low silicate very high Fe and Mg Ex Periodite Magmatic differentiation Magma does not all melt or solidify at one temperature because it is composed of different minerals of different compositions parts of it melt at different times More Felsic More Mafic Low melting temp high melting temp Crystalize 1st crystalize last Low Density High Density Factors of melting temps High Melting temp mafic Low Melting temp felsic High Pressure Low Pressure Low water content High water content Bowens reaction series The more mafic minerals in a magma will crystalize first and settle the magma chamber floor This changes the composition