University:
California State University, Northridge
Course:
GEOL 101 | Geology of Planet Earth
Academic year:

2024
Views:

22

Pages:

19
Author:

Braelyn Reeves

Geologic Resources and Earth’s Systems • Geologic resources - valuable materials of geologic origin that can be extracted from the Earth – Many geologic resources originate in the hydrosphere • Petroleum and coal come from organisms that lived and died in water • Halite (salt) and other evaporite minerals come from dry lake beds – Weathering interactions between geosphere, atmosphere and hydrosphere produce metal oxide ores – Humans (biosphere) interact directly with the geosphere, hydrosphere, and atmosphere when extracting and utilizing geologic resources – Groundwater (hydrosphere) is a renewable geologic resource • If it can’t be grown, it must be mined Types of Geologic Resources • Geologic resources are grouped into three major categories: – Energy resources - petroleum (oil and natural gas), coal, uranium, geothermal resources – Metals - iron, copper, aluminum, lead, zinc, gold, silver, platinum – Non-metallic resources - sand and gravel, limestone, building stone, salt, sulfur, gems, gypsum, phosphates, groundwater, etc. Resources and Reserves • Resources - the total amount of a valuable geologic material in all deposits, discovered and undiscovered • Reserves - discovered deposits of geologic resources that can be extracted economically and legally under present conditions – The short-term supply of a geologic materials Energy Resources - Coal • Fossil fuels (oil, natural gas, and coal) account for nearly 90% of U.S. energy • Coal is a sedimentary rock that forms from the compaction of plant material that has not completely decayed – Forms from shallow burial and compaction of peat Energy Resources - Coal • Four varieties of coal – Lignite (brown coal) is soft and crumbly – Sub-bituminous and bituminous coal (soft coal) • black and dusty • burn with a smoky flame • commonly strip-mined – Anthracite (hard coal) • shiny and dust-free • burns with a smokeless flame • low-level metamorphic rock • Burning of high-sulfur coal can produce acid rain; strip mines can scar landscape • U.S. coal reserves could last for centuries Energy Resources -Petroleum • Petroleum - oil and natural gas - occurs in underground pools • Occurrence of oil pools requires: – A source rock (rich in organic matter) – A reservoir rock in which it can be stored and transmitted (e.g., sandstone) – An oil trap (set of conditions holding rock in reservoir rock and preventing migration) – Deep enough burial (and sufficient time) to “cook” the oil and gas out of the organic matter Structural Traps for Gas and Oil Energy Resources - Petroleum Eroded anticline forms trap in Landers oil field in Wyoming. Other Oil Traps in Geological Structures Petroleum Recovery • Oil fields are regions underlain by one or more oil pools – Largest in U.S. are in Texas and Alaska • Oil and natural gas are removed through wells drilled down into an oil trap within a reservoir rock • Negative environmental effects resulting from oil recovery and transport include oil spills, brine contamination of surface water, and ground subsidence Oil Peak, Oil Panic ? (Study by Amos Nur - Stanford) U.S., Canada, Japan, Germany, France, Italy, UK, are the biggest consumers of oil reserves worldwide. Oil Peaks – 1960's In the 1850's oil mainly used for kerosene lamps – remaining was burned or disgarded. Current oil production rates peaked in 1960's but U.S. consumption rates increase dramatically above this. Don't panic! -Try to conserve energy -Seek alternative energy sources Petroleum Reserves At current rate of use, worldwide oil reserves should last 30-40 years, and natural gas reserves somewhat longer (estimates from USGS) Oil future and war now... Countries with highest per capita income seeking oil from countries holding the oil wells/reservoirs (Saudi Arabia, Iraq, Venezuala). Petroleum Reserves • As petroleum prices rise, alternate petroleum sources, such as heavy crude, oil shale and oil sand, will be increasingly exploited – Heavy crude is dense, viscous petroleum – Oil shale is black or brown shale with high solid organic matter content from which oil can be extracted by distillation – Oil sands (or tar sands) are asphalt-cemented sand or sandstone deposits Other Energy Resources • The metal uranium is used to power nuclear power generators – Typically found in association with organic matter in sedimentary rocks – Accounts for 10% of U.S. energy production – Leaves radioactive waste as by-product • Hydroelectric power provides about 4% of U.S. energy needs – Renewable and non-polluting • Geothermal power provides about 0.2% of U.S. energy needs • Other renewable, non-polluting energy sources are wave/current power, solar power, wind power, and hydrogen fuel cells – As fossil fuel supplies dwindle, these sources must become more important Metals and Ores • Metal ores - naturally occurring materials that can be profitably mined • Whether or not a mineral deposit is an ore depends on chemical composition, the percent extractable metal, and current market value of the metal • Metallic ore deposits originate from crystal settling in igneous intrusions, hydrothermal fluids cooling in pores and factures, chemical precipitation in water, or sedimentation in rivers (placers) Mining and Metals • Mining can be done at Earth’s surface (strip mines, open-pit mines, and placer mines) or underground – Metals mined include iron, copper, aluminum, lead, zinc, silver, gold and many others • With care, negative environmental effects of mining, including unsightly tailings piles, surface scars, land subsidence, and acid mine drainage can be minimized Non-metallic Resources • Non-metallic resources - not mined to extract a metal or an energy source – construction materials • sand, gravel, limestone, and gypsum – agriculture • phosphate, nitrate and potassium compounds) – industrial uses • rock salt, sulfur, asbestos) – gemstones • diamonds, rubies, etc. – household and business products • glass sand, fluorite, diatomite, graphite)

Geologic Resources and Earth’s Systems

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