Exam Review ERS103

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Earth Science
John Johnston

EXAM REVIEW ERS103 Chapter 12 – Energy and Mineral Resources Energy: simply the capacity to do work, to cause something to happen, or to cause change in a system. Resource: We refer to any material that can be of use, either to make something or to provide energy as a resource. Energy Resource: Something that can be used to produce work; in a geological context, a material (such as oil, coal, wind, flowing water) that can be used to produce energy. Mineral Resource: The minerals extracted from the Earth’s upper crust for practical purposes. * Humans obtain energy from a variety of sources. Some are physical (such as solar radiation and gravity), whereas others are biological (involving plant growth): - Energy directly from the Sun (solar panels and water heating) - Energy directly from gravity (movement of water powers turbines) - Energy involving both solar energy and gravity (wind powers sails and windmills. Water cycle powers waterwheels and turbines.) - Energy via photosynthesis (burning plant mass to create energy, like plant material to create ethanol. - Energy from chemical reactions (Dynamite, hydrogen fuel cells) - Energy from fossil fuels (oil, gas, coal) - Energy from nuclear fission (Nuclear energy plants) - Energy from Earth’s internal heat (heats underground water and when water turns to steam creates geothermal energy) Hydrocarbons: chain-like or ring-like molecules made of carbon and hydrogen atoms. Chemists consider hydrocarbons to be a type of organic chemical. Source Rock: A rock (organic-rich shale) containing the raw materials from which hydrocarbons eventually form. Kerogen: The waxy molecules into which the organic material in the shale transforms on reaching about 100C. At higher temperatures, kerogen transforms into oil. Oil Shale: Shale containing kerogen. Oil Window: The narrow range of temperatures under which oil can form in a source rock. * Oil and gas are hydrocarbons whose atoms come from algae and plankton. When the organisms die, their bodies mix with clay to produce organic ooze on the floor of quiet lakes and seas. Burial transforms the ooze into black shale, a source rock. At temperatures of between 90 and 160C the organic material in black shale turns into oil. Reservoir Rock: Is a rock that contains or could contain an abundance of easily extractable oil and gar. The rock must have a high porosity and permeability (how well the pore space connects with each other). Porosity refers to the amount of open space (pore space) in a rock. Trap: In the context of hydrocarbon, a trap is a geological configuration that accumulates and holds oil underground. * Oil and gas reserves develop only where there is an appropriate source rock (black shale), a migration pathway, a reservoir rock (such a porous and permeable sandstone), and a trap that keeps oil and gas underground. Hydrocarbons rise because they are buoyant. * Searching for oil is a complex and expensive process. Geologists use seismic- reflection profiles to locate possible traps. Drilling taps reserves and pumping brings crude oil to the surface, where it is processed at refineries that crack hydrocarbon molecules. Tar Sand: Sandstone reservoir rock in which less viscous oil and gas molecules have either escaped or been eaten by microbes, so that only tar remains. Gas Hydrate: is a chemical compound consisting of a methane (CH4) molecule surrounded by a cage-like arrangement of water molecules. An ice like solid consisting of water and methane. Coal Rank: A measurement of carbon content of coal; higher-ran coal forms at higher temperatures. Coal Gasification: The process of producing clean-burning gases from solid coal by transforming coal into gases as well as solid byproducts before burning. * Coal forms from the remains of plant material. When buried deeply, this organic material undergoes reactions that concentrate carbon; high-rank coal contains more carbon. Coal occurs in sedimentary successions and must be mined underground or in open pits. * Controlled fission in reactors produces nuclear power. The fuel consists of uranium or other elements obtained by mining. Reactors run the risk of meltdown, though this has not yet happened. Reactors also produce radioactive waste that is difficult to store. Ore: Rock containing native metals or a concentrated accumulation of ore minerals. Ore minerals have metal in high concentrations and in a form that can be easily extracted. * Ores can be processed economically to produce metals. Ores form by: settling from melt, precipitating from hot water, deposition from currents, interaction with groundwater, and extreme weathering. The distribution of ores can be explained by plate tectonics. Aggregates: A non‐renewable resource that consists of any combination of sand, gravel, or crushed stone (bedrock). This resource is literally the “foundation” of our modern society that we use and benefit from every day. Chapter Summary - Energy comes from a variety of sources: directly from the Sun; from tides, flowing water, or wind; from chemical reactions; from nuclear fission; and from Earth’s internal heat. Plants use photosynthesis to store energy. Buried organic matter becomes fossil fuel. - Oil and gas are hydrocarbons. The viscosity and volatility of a hydrocarbon depend on the length of its molecules. - Oil and gas form from the bodies of plankton and algae, which settle out in a quiet-water, oxygen-poor depositional environment and form black organic shale. Later, chemical reactions at elevated temperatures convert the organic matter into kerogen, then oil. - In order to create a usable oil reserve, oil must migrate from a source rock into a reservoir rock. Unless the reservoir rock is overlain by an impermeable seal rock, the oil will escape to the group surface. The subsurface configuration of strata that leads to the entrapment of oil is called and oil trap. - Substantial volumes of hydrocarbons exist in tar sand, oil, shale, and gas hydrate. - For coal to form, plant material must be deposited in an oxygen-poor environment so that it does not decompose. Compaction creates peat, which, when buried deeply and heated, transforms into coal. - Coal is classified into ranks, based on the amount of carbon it contains. Coal occurs in beds, interlayered with other sedimentary rocks, and can be mined by either strip mining or underground mining. - Coalbed methane and coal gasification provide additional sources of energy. - Nuclear power plants generate energy by using the heat released by the fission of uranium. The heat turns water into steam, and the steam drives turbines. Some economic uranium deposits occur as veins in igneous rock bodies, while others are found in sedimentary beds. - Nuclear reactors must be carefully controlled to avoid overheating or meltdown. The disposal of radioactive nuclear waste can create environmental problems. - Geothermal energy uses Earth’s internal heat to transform groundwater into steam that drives turbines; hydroelectric power plants use the potential energy of water; and solar cells convert sunlight to electricity. - We now live in the Oil Age, but oil supplies may only last for another century. - Use of energy resources has many negative environmental consequences. - Industrial societies use many types of minerals, all of which must be extracted from the upper crust. We distinguish two general categories: metallic resources and non-metallic resources. - Metals come from ore. An ore is a rock containing native metals or ore minerals (minerals with a high proportion or metal) in sufficient quantities to be worth mining. An ore deposit is an accumulation of ore. - Magmatic deposits form when sulfide ore minerals settle to the floor of a magma chamber. In hydrothermal deposits, ore minerals precipitate from hot-water solutions. Secondary enrichment deposits. MVT deposits precipitate from groundwater that has passed long distances through the crust. Sedimentary deposits precipitate out of the ocean. Residual mineral deposits in soil are the result of severe leaching in tropical climates. Placer deposits develop when heavy metal grains accumulate in sediment along a stream. - Many ore deposits are associated with igneous activity in subduction zones, along mid-ocean ridges, along continental rifts, or at hot spots. - Nonmetallic resources include dimension stone for decorative purposes, crushed store for cement and asphalt production, clay for brick making, sand for glass production, and many others. A large proportion of materials in your home have a geological ancestry. - Mineral resources are nonrenewable. Many are now or may soon be in short supply. Chapter 18 – Glaciers and Ice Ages * In order for a Glacier to form, three conditions must be met. - The local climate must be sufficiently cold that winter snow does not melt away entirely during the summer. - There must be or must have been sufficient snowfall for a large amount to accumulate. - The slope of the surface on which the snow accumulates must be gentle enough that the snow does not slide away in avalanches, and must be protected enough that the snow doesn’t blow away. * The transformation of fresh snow to glacier ice can take as little as tens of years in regions with abundant snowfall, or as long as thousands of years in regions with little snowfall. Mountain Glaciers: A glacier that exists in or adjacent to a mountainous region. Continental Glaciers: A vast sheet of ice that spreads over thousands of square kilometers of continental crust. Temperate Glaciers: occur in regions where atmospheric temperatures become high enough for the glacial ice to be at or near its melting temperature for part of the year. Polar Glacier: occur in regions where atmospheric temperatures stay so low that the glacial ice remains well below melting temperature through the year. Basal Sliding: The phenomenon in which meltwater accumulates at the base of a glacier, so that the mass of the glacier slides on a layer of water or on a slurry of water and sediment. Plastic Deformation: The deformational process in which mineral grains behave like plastic and, when compressed or sheared, become flattened or elongate without cracking or breaking. * Glaciers form when deeply buried snow turns to ice and recrystallizes. Mountain glaciers form at high elevation and can flow down valleys; ice sheets form in polar latitudes and spread over continents. Depending on the balance of accumulation to ablation, glaciers can advance or retreat. * A glacier scrapes up and plucks rocks from it substrate, and carries debris that falls on its surface. Glacial erosion polishes and scratches rock and carves distinctive landforms, such as U-shaped valleys. Since ice is solid, moving ice does not sort sediment. * When ice melts, it drops unsorted sediment to form glacial till, Meltwater streams and wind can transport and sort the sediment to form outwash plains and loess deposits, respectively. Deposition by glaciers produces distinctive landforms, such as moraines. * The weight of a continental ice sheet can cause the ground surface to sink. When the glacier melts away, the surface slowly rises. Continental ice sheets store significant amounts of water. As a consequence, growth or melting of ice sheets affects sea level. * Regions that are cold most of the yea, but are not glaciated, may be underlain by permanently frozen ground (permafrost). Summer melting may turn the top few meters into mud. Freeze and thaw cycles produce patterned ground. * During the last Ice Age, which began about 3 Ma, continental ice sheets advanced and retreated several times. This period includes the Pleistocene (which formally began 1.8 Ma, and ended about 11 Ka). Other ice ages happened earlier in Earth history. * Ice ages happen when the distribution of continents, ocean currents, and the concentration of atmospheric CO2 are appropriate. Advances and retreats during an ice age are controlled by Milankocitch cycles (variations in Earth’s aobit shape and in the orientation of Earth’s rotation axis). Chapter Summary - Glaciers are streams or sheets of recrystallized ice that survive for the entire year and flow in response to gravity. Mountain glaciers exist in high regions and fill cirques and valleys. Continental glaciers (ice sheets) spread over substantial areas of the continents. - Glaciers form when snow accumulates over a long period of time. With progressive burial, the snow first turns to firn then to ice. - Glacial ice moves by basal sliding over water or wet sediment over water or wet sediment, and/or by internal flow. In general, glacial ice moves tens of meters per year. - Whether the toe of a glacier stays fixed in position, advances farther from the glaciers origin, or retreat back toward the origin depends on the balance between the rate at which snow builds up in the zone of accumulation and the rate at which glaciers melt or sublimate in the zone of ablation. - Glacial ice can flow over sediment or incorporate sediment. The clasts embedded in glacial ice act like a rasp that abrades the substrate. - Mountain glaciers carve numerous landforms, including cirques, arêtes, horns, U-shaped valleys, hanging valleys, and truncated spurs. Glacially carved valleys that fill with water when sea level rises after an ice age are fjords. - Moraines are piles or ridges of glacial till. Till is unsorted sediment, which accumulates because glaciers can transport sediment of all sizes. - Glacial depositional landforms include moraines, knod-and-kettle topography, drumlins, eskers, meltwater lakes, and outwash plains. - Continental crust subsides as a result of ice loading. When the glacier melts away, the crust rebounds. - When water is stored in continental glaciers, sea level drops. When glaciers melt, sea level rises. - During past ice ages, the climate in regions south of the continental glaciers was wetter, and pluvial lakes formed. Permafrost exists in periglacial environments. - During the Pleistocene ice age, large continental glaciers covered much of North America, Europe, and Asia. - The stratigraphy of glacial deposits indicates that glaciers advanced and retreated many times during the Pleistocene. Long-term causes of ice ages include plate tectonics and changes in the concentration of CO2 in the atmosphere. Short-term causes include the Milankovitch cycles (caused by periodic changes in Earth’s orbit and tilt). Chapter 19 – Global Change in the Earth System Global Change: The transformations or modifications of both physical and biological components in the Earth System through time. * Since it first formed, the Earth has undergone major changes that are unidirectional, in that they will never repeat. Examples include the formation of the core, mantle, and moon; the evolution of the atmosphere and oceans; and the evolution of life. Supercontinent Cycle: The process of change during which supercontinents form and later break apart. Geologists have found evidence that at least three or four times during the past 3 billion years of Earths history, supercontinents existed. The most recent on, Pangaea, formed at the end of the Paleozoic Era. * The crust of the Earth consists of three rock types: ingenous, sedimentary, and metamorphic. Biogeochemical cycle: The passage of a chemical among nonliving and living reservoirs in the Earth System, mostly on or near the surface. Nonliving reservoirs include the atmosphere, the crust, and the ocean; living reservoirs include plants, animals, and microbes. Greenhouse Gases: Atmospheric gases, such as carbon dioxide and methane, that regulate the Earth’s atmospheric temperature by absorbing infrared radiation. * In the Earth System, chemicals – such as carbon and water – cycle through living and non-living reservoirs. For example, carbon can be stored in the atmosphere and CO2, in seawater as bicarbonate ions, in rock as calcite, and in fossil fuels as oil, gas, and coal. Climate: The average range of weather conditions for a given region. * If the average atmospheric and sea surface temperature rises, we have global warming; if it falls, we have global cooling. Mass-extinction events: When large numbers of species abruptly vanish. * Earth’s past climate can be studied using fossils, isotopes, pollen assemblages, and growth rings in trees. The record shows that, over geological time, climate alternates between warm (greenhouse) conditions and cold (icehouse) conditions. Volcanic eruptions and meteorite impacts can cause catastrophic change. * Humans have become major agents of change in the Earth System. Human activities modify the landscape, disrupt ecosystems, and decrease forest cover. Evidence gathered in recent decades indicates that the release of greenhouse gases causes global warming. Sustainable growth: An ability to prosper within the constraints of the Earth System. * In the near term, Earth’s surface will be affected by decisions of human society. Over longer time scales, the map of the Earth will change due to plate interactions and sea-level change. The end of the Earth will happen when the Sun becomes a red giant. Chapter Summary - We refer to the global interconnecting web of physical and biological phenomena on Earth as the Earth System. Global change involves the transformations or modifications of physical and biological components of the Earth System through time. Unidirectional change results in transformations that never repeat; cyclic change involves repetition of the same steps over and over. - Examples of unidirectional change include the gradual evolution of the solid Earth from a homogenous collection of planetesimals to a layered planet, the formation of the oceans, the gradual change in the composition of the atmosphere, and the evolution of life. - Examples of physical cycles that take place on Earth include the supercontinent cycle, the sea-level cycle, and the rock cycle. - A biochemical cycle involves the passage of a chemical among nonliving and living reservoirs. Examples include the hydrologic cycle and the carbon cycle. Global change occurs when factors change the relative proportions of the chemical in different reservoirs. - Tools for documenting global climate change include the stratigraphic record, paleontology, oxygen-isotope ratios, and growth rings. - Studies of long-term climate change show that at times in the past the Earth experience greenhouse (warmer) periods. Factors leading to long- term climate change include the positions of continents, volcanic activity, the uplift of land, and the formation of materials that remove CO2, an important greenhouse gas. - Short-term climate change can be seen in the record of the last million years. In fact, during only the past 15,000 years, we see that the climate has warmed and cooled a few times. Causes of short-term climate change include fluctuations in solar radiation and cosmic rays, changes in Earth’s orbit and tilt, changes in reflectivity, and changes in ocean currents. - Mass extinction, a catastrophic change in biodiversity, may be caused by the impact of a comet or asteroid or by intense volcanic activity. - During the last two centuries, humans have changed landscapes, modified ecosystems, and added pollutants to the land, air, and water at rates faster than the Earth System can process. - The addition of CO2 and CH4 to the atmosphere may be causing global warming, which could shift climate belts and lead to a rise in sea level. - In the future, in addition to climate change, the Earth will witness a continued rearrangement of continents resulting from plate tectonics, and will likely suffer the impact of asteroids and comets. The end of the Earth may come when the Sun runs out of fuel in about 5 billion years and becomes a red giant. Chapter 8 – Earthquakes * Most earthquakes happen due to sudden rupture of rock accompanying the formation or reactivation of a fault. A hypocenter is the location in the Earth where a
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