Earth Rocks Chapter Notes.docx

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Earth Sciences
Earth Sciences 1022A/B
Stephen R Hicock

Geology 9/17/2012 9:25:00 PM Geology – science that examines earth, its form and composition, and the changes that it has undergone and undergoing. Physical Geology – a major division of geology that examines the materials of earth and seeks to understand the processes and forces acting beneath and on earth’s surfaces. Historical geology – a major division of geology that deals with the origin of earth and its development through time. Usually involves the study of fossils and their sequence in rock beds. Outcrops – where bedrock is exposed at the surface Geologic hazards are natural processes, they become hazards when people decide to live there Resources – endowment of materials held in reserve that are useful to people and are ultimately available commercially. Types of resources  Water  Soil  Metallic and nonmetallic minerals  Energy Catastrophism – The concept that earth was shaped catastrophic events of a short-term nature. Uniformitarianism – the physical, chemical, and biologic laws that operate today have also operate today have also operated in the geologic past. The forces and processes that we observe presently shaping our planet have been at work for a very long time. This idea is summarized by, “The present is the key to the past” Relative Dating – The placing of rocks and structures in their proper sequence of order. Only the chronologic order events are determined. Law of superposition – In any undeformed sequence of sedimentary rocks, each bed is older than the one above and younger than the one below. Fossils – the remains or traces of prehistoric life Principle of fossil succession – fossil organisms succeed one another in a definite and determinable order, and therefore any time span can be recognized by its fossil content. Crust – The very thin outermost layer of Earth Nebular Hypothesis – A model for the origin of the solar system that supposes a rotating nebula of dust and gases that contracted to form the Sun and planets. Core – The innermost layer of Earth based on composition. It is thought to be largely an iron-nickel alloy with minor amounts of oxygen, silicon, and sulphur. Mantle – One of Earth’s compositional layers. The solid rocky shell that extends from the base of the crust to a depth of 2900 kilometres. Continental Drift – Alfred Wegener’s hypothesis that suggested all present continents once existed as a single supercontinent. Continents started drifting apart about 200 million years ago. Paradigm – A theory that is held with a very high degree of confidence and is comprehensive in scope. Plate Tectonics – The theory that proposes that Earth’s outer shell consists of individual plates that interact in various ways and thereby produce earthquakes, volcanoes, mountains, and the crust itself. Pangaea – The proposed supercontinent that 200 million years ago began to break apart and form the present landmasses. Continental Shelf – The gently sloping submerged portion of the continental margin, extending from the shoreline to the continental slope. Lithosphere – The rigid outer layer of Earth, including the crust and uppermost mantle. Divergent Plate Boundary – A boundary in which two plates move apart, resulting in upwelling of material from the mantle to create new seafloor. Mid-ocean Ridge – A continuous mountainous ridge on the floor of all the major ocean basins. Floor Spreading – hypothesis proposed by Harry Hess suggested that new oceanic crust is produced at mid-ocean ridges, which are the sites of divergence. Convergent Plate Boundary – Boundary in which two plates move together, resulting in the descent of oceanic lithosphere into the mantle. Or two continental margins collide to create a major mountain system. Subduction – Process by which oceanic lithosphere plunges into the mantle along a convergent zone. Subduction Zone – A long, narrow zone in which ne lithosphere plate descends beneath another. Transform Fault Boundaries – Boundary in which two plates slide past each other without creating or destroying the lithosphere. Mesophere – The part of the mantle that extends from the core-mantle boundary to a depth of 660 kilometres. It is also known as the lower mantle. Outer Core – A layer beneath the mantle about 2270 kilometres thick, which has the properties of a liquid. Inner Core – The solid innermost layer of Earth, about 1216 kilometres in radius. Hydrosphere – The water portion of our planet; one of the traditional subdivisions of Earth’s physical environment. Atmosphere – The gaseous portion of a planet; the planet’s envelope of air. One of the traditional subdivisions of Earth’s physical environment. Biosphere – The totality of life forms on Earth. Shields – A large, relatively flat expanse of ancient metamorphic and igneous rock within the stable continental interior. System – A group of interacting or interdependent parts that form a complex whole. Igneous Rock – Rock formed from the crystallation or solidification of magma or lava. Sediment – A material that settles out in particulate form from a fluid, either from gravitational factors of precipitation. Sedimentary Rock – The rock formed from the weathered products of preexisting rocks that have been transported, deposited, and lithified. Metamorphic Rock – Rock formed by the alteration of preexisting rock deep within Earth (but still in the solid state) by heat, pressure, and/or chemically active fluids. Minerals 9/17/2012 9:25:00 PM Mineralogy – The study of minerals Minerals – A naturally occurring inorganic crystalline solid material with a specific chemical composition structure. Rock – A consolidated mixture of minerals. Atom – The smallest particle that exists as an element. Proton – A positively charged subatomic particle found in the nucleus of an atom. Neutron – A subatomic particle found in the nucleus of an atom. The neutron is electrically neutral, with a mass approximately equal to that of a proton. Electron – A negatively charged subatomic particle that has a negligible mass and is found outside an atom’s nucleus. Atomic Number – The number of protons in the nucleus of an atom. Atomic Weight – The average of the atomic masses of the isotopes for a given element. Valence Electrons – The electrons involved in the bonding process; the electrons occupying the highest principal energy level of an atom. Compound – A substance formed by the chemical combination of two or more elements in definite proportions and usually having properties different from those of its constituent elements. Ionic Bond – A chemical bond between two oppositely charged ions formed by the transfer of valence electrons from one atom to another. Polymorphs – Two or more minerals that have the same chemical composition but different crystalline structures. They are exemplified by the diamond and graphite forms of carbon. Crystal Habit – The external expression of a mineral that reflects the orderly internal arrangement of atoms. Lustre – The appearance or quality of light reflected from the surface of a mineral crystal. Colour- A phenomenon of light by which otherwise identical objects can be differentiated. Streak – The colour of a mineral in its powdered form and is obtained by rubbing the mineral across a piece of unglazed porcelain. Hardness – Measure of a mineral’s resistance to abrasion or scratching. Mohs scale – A series of 10 minerals used as a standard in determining hardness. Cleavage – The tendency of a mineral to break along planes of weak bonding. Fracture – Any break or rupture in rock along which no appreciable movement has taken place. Specific Gravity – A number representing the ratio of the weight of a mineral to the weight of an equal volume of water. Silicon-oxygen tetrahedron – A pyramid-shaped structure composed of four oxygen atoms surrounding a silicon atom that constitutes the basic building blocks of silicate minerals. Dark Silicates (Ferromagnesian silicates) – Silicate minerals that contain ions of iron or magnesium (or both) in their structure. They are dark in colour and have a higher specific gravity than nonferromagnesian silicates. Light Silicates (nonferromagnesian silicates) – Silicate minerals that lack iron or magnesium. They are generally lighter in colour and have lower specific gravities than dark silicates. Igneous Rocks 9/17/2012 9:25:00 PM Igneous Rocks – Rock formed from crystallization or solidification of magma or lava. Partial Melting – The process by which most igneous rocks melt. Because individual minerals have different melting points, most igneous rocks melt over a temperature range of a few hundred degreed. If the liquid is squeezed out after some melting has occurred, a melt with a higher silica content results. Extrusive – The igneous activity that occurs at Earth’s surface. Volcanic – Pertaining to the activities, structures, or rock types of a volcano. Intrusive Rock – The igneous rock that formed below Earth’s surface. Plutonic Rock – The igneous rock that forms at depth. Named after Pluto, the god of the underworld in classical mythology. Pluton – A body of plutonic rock. Geothermal Gradient – The gradual increase in temperature with depth in the crust. The average is 25° C per kilometer in the upper crust. Volatiles – The gaseous components of magma dissolved in the melt. Volatiles readily vaporize (form a gas) at surface pressures. Decompression Melting – The melting that occurs because of a drop in confining pressure as rock ascends. Mafic Composition (basaltic composition) – A compositional group of igneous rocks characterized by a substantial proportion of dark, magnesium and iron-rich silicate minerals and calcium-rich plagioclase feldspar. Felsic Composition (granitic composition) – A compositional group of igneous rocks indicating the rock is composed almost entirely of light- coloured silicates. Magma – A body of molten material found at depth, including any dissolved gases and crystals. Melt – The liquid portion of magma excluding the solid crystals. Crystallization – The formation and growth of a crystalline solid from a liquid or gas. Crystal Settling – During the crystallization of magma, the earlier-formed minerals are denser than the liquid portion and settle to the bottom of the magma chamber. Magmatic Differentiation – The process of generating more than one rock type from a single magma. Bowen’s Reaction Series – A concept proposed by N.L. Bowen that illustrates the relationships between magma and the minerals crystallizing from it during the formation of igneous rocks. Assimilation – In igneous activity, the process of incorporating country rock into a magma body. Magma Mixing – The process of altering the composition of a magma through the mixing of material from another magma body. Intermediate Composition (andesitic composition) – A compositional group of igneous rocks, indicating that the rock contains at least 25 percent dark silicate minerals. The other dominant mineral is plagioclase feldspar. Ultramafic Composition – A compositional group of igneous rocks that contain mostly olivine and/or pyroxene. Texture – The size, shape, and distribution of the particles that collectively constitute a rock. Glass – the natural glass produced when molten lava cools too rapidly to permit crystallization. Volcanic glass is a solid composed of unordered atoms. Aphanitic Texture – A texture of igneous rocks in which the crystals are too small for individual minerals to be distinguished without magnification. Vesicular Texture – A term applied to aphanitic igneous rocks that contain many small cavities called vesicles. Phaneritic Texture – An igneous rock texture in which the crystals are roughly equal in size and large enough so the individual minerals can be identified without magnification. Porphyritic Texture – An igneous rock texture characterized by two distinctively different crystal sizes. The larger crystals are called phenocrysts, wheras the matrix of smaller crystals is termed the groundmass. Phenocrysts – Conspicuously large crystals embedded in a matrix of finergrained crystals. Groundmass – The matrix of smaller crystals within an igneous rock that has porphyritic texture. Porphyry – An igneous rock with a porphyritic texture. Glassy – A term used to describe the texture of certain igneous rocks, such as obsidian, that contain no crystals. Pyroclastic Texture – An igneous rock texture that results from the consolidation of individual rock fragments that are ejected during a violent volcanic eruption. Pegmatite – A very coarse-grained igneous rock (typically granite) commonly found as a dyke associated with a large mass of plutonic rock that has smaller crystals. Crystallization in a water-rich environment is believed to be responsible for the very large crystals. Pegmatitic Texture – A texture of igneous rocks in which most of the interlocking crystals are all larger than 1 centimetre in diameter. Tabular – The description of a feature, such as an igneous pluton, that has two dimensions that are much longer than the third. Massive – An igneous pluton that is not tabular in shape. Discordant – A term used to describe plutons that cut across existing rock structures, such as bedding planes. Concordant – A term used to describe intrusive igneous masses that form parallel to the bedding of the surrounding rock. Dyke – A tabular-shaped intrusive igneous feature that cuts through the surrounding rock. Sill – A tabular igneous body that was intruded parallel to the layering of preexisting rock. Columnar joints – A pattern of cracks that form during cooling of molten rock to generate columns. Batholith – A large mass of igneous rock formed by the emplacement and crystallization of magma at depth. Stock – A pluton similar to but smaller than a batholith. Xenolith – An inclusion of unmelted country rock in an igneous pluton. Volcanoes 9/17/2012 9:25:00 PM Viscosity – A measure of a fluid’s resistance to flow. Vent – The surface opening of a conduit or pipe in a volcano. Conduit – A pipe-like opening through which magma moves towards Earth’s surface. It terminates at a surface opening called a vent. Eruption Columns – Buoyant plumes of hot, ash-laden gases that can extend thousands of metres into the atmosphere. Pahoehoe Flow – A lava flow with a smooth to ropy surface. Aa flow – A type of lava flow that has a jagged, blocky surface. Pillow Lava – Basaltic lava that solidifies in an underwater environment and develops a structure that resembles a pile of pillows. Lava Tube – A tunnel in hardened lava that acts as a horizontal conduit for lava flowing from a volcanic vent. Lava tubes allow fluid lavas to advance great distances. Pyroclastic Material – The volcanic rock ejected during an eruption. Pyroclastics include ash, bombs, and blocks. Scoria – The vesicular ejecta that is the product of basaltic magma. Pumice – A light-coloured glassy vesicular rock commonly having a felsic composition. Pyroclastic flow – A highly heated mixture, largely of ash and pumice fragments, travelling down the flanks of a volcano or along the surface of the ground. Nuee ardente – Incandescent volcanic debris buoyed up by hot gases that moves downslope in an avalanche fashion. Lahar – The debris flows on the slopes of volcanoes that result when unstable layers of ash and debris become saturated and flow downslope, usually following stream channels. Pipe – A vertical conduit through which magmatic materials have passed. Volcano – A mountain formed from lava or pyroclastics. Crater – The depression at the summit of a volcano or one produced by a meteorite impact. Caldera – A large depression typically caused by collapse or ejection of the summit area of a volcano. Parasitic Cone – A volcanic cone that forms on the flank of a larger volcano. Fumarole – A vent in a volcanic area from which fumes or gases escape. Shield volcano – A broad, gently sloping volcano built from fluid basaltic lavas. Cinder cone – A rather small volcano built primarily of ejected lava fragments that consist mostly of pea to walnut size lapilli. Composite cone – A volcano composed of both lava flows and pyroclastic material. Fissure – A crack in rock along which there is a distinct separation. Fissure eruption – An eruption in which lava is extruded from narrow fractures or cracks in the crust. Flood Basalts – The flows of basaltic lava that issue from numerous cracks or fissures and commonly cover extensive areas to thicknesses of hundreds of metres. Lava Dome – A bulbous mass associated with an old-age volcano, produced when thick lava is slowly squeezed from the vent. Lava domes can act as plugs to deflect subsequent gaseous eruptions. Volcanic Neck – An isolated, steep sided, erosional remnant consisting of solidified magma that once occupied the vent of a volcano. Intraplate volcanism – The igneous activity that occurs within a lithospheric plate away from plate boundaries. Weathering and Soil 9/17/2012 9:25:00 PM Internal processes – Processes such as mountain building or volcanism, that derive its energy rom Earth’s interior and elevate Earth’s surface Weathering – The physical breakdown (disintegration) and chemical alteration (decomposition) of roc
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