ENSP101 Chapter 14 Geology and Earth Resources 14 1 Earth Processes Shape Our Resources Core the dense intensely hot mass of molten metal mostly iron and nickel thousands of km s in diameter at the earth s enter Mantle a hot pliable layer of rock that surrounds the earth s core and underlies the cool outer crust Crust the cool lightweight outermost layer of the earth s surface that floats on the soft pliable underlying layers Tectonic plates huge blocks of the earth s crust that slide around slowly pulling apart to open new ocean basins or crashing ponderously into each other to create new larger landmasses o These plates slide slowly across the earth s surface like wind driven ice sheets on water in some places breaking up into smaller pieces in other places crashing ponderously into each other to create new larger landmasses o Ocean basins form where continents crack and pull apart o Magma molten rock from deep in the earth s interior called lava when it spews from volcanic vents Mid ocean ridges mountain ranges on the ocean floor created where molten magma is forced up through cracks in the planet s crust Creating the largest mountain range in the world these ridges wind around the earth for 74 000 km Although concealed from our view this jagged range boasts higher peaks deeper canyons and sheerer cliffs than any continental mountains o Earthquakes are caused by grinding and jerking as plates slide past each other o When an oceanic plate collides with a continental landmass the continental plate usually rides up over the seafloor while the oceanic plate is subducted or pushed down into the mantle where it melts and rises back to the surface as magma o Deep ocean trenches mark these subduction zones and volcanoes form where the magma erupts through vents and fissures in the overlying crust o Over millions of years continents can drift long distances o The redistribution of continents has profound effects on the earth s climate and may help explain the periodic mass extinctions of organisms marking the divisions between many major geologic periods 14 2 Rocks and Minerals Mineral a naturally occurring inorganic crystalline solid with definite chemical composition and characteristic physical properties o The 2 fundamental characteristics of a mineral that distinguish it from all other minerals are its chemical composition and its crystal structure No 2 minerals are identical in both respects Rock a solid cohesive aggregate of one or more minerals o Within the rock individual mineral crystals or grain are mixed together and held firmly in a solid mass o The grains may be large or small depending on how the rock was formed but each grain retains its own unique mineral qualities o Rock cycle the process whereby rocks are broken down by chemical and physical forces sediments are moved by wind water and gravity sedimented and reformed into rock and then crushed folded melted and re crystallized into new forms o There are 3 major rock classifications igneous sedimentary and metamorphic Igneous Metaphoric Sedimentary Igneous rocks crystalline minerals solidified from molten magma from deep in the earth s interior balat rhyolite andesite lava and granite are examples The most common rock type in the earth s crust is solidified form magma welling up from the earth s interior Preexisting rocks can be modified by heat pressure and chemical agents to create new forms called metamorphic rock Weathering and sedimentation wear down rocks Most of these crystalline rocks are extremely hard and durable but exposure to air water changing temperatures and reactive chemical agents slowly breaks them down in a process called weathering o Mechanical weathering is the physical breakup of rocks into smaller particles without a change in chemical composition of the constituent minerals o Chemical weathering is the selective removal or alteration of specific components that leads to weakening and disintegration of rock o Among the more important chemical weathering processes are oxidation combination of oxygen with an element to form an oxide or hydroxide mineral and hydrolysis hydrogen atoms from water molecules combine with other chemicals to form acids Sedimentation the deposition of organic materials or minerals by chemical physical or biological processes Sedimentary rock deposited material that remains in place long enough or is covered with enough material to compact into stone examples include shale sandstone breccia and conglomerates Sedimentary rocks are also formed from crystals that precipitate out of or grow from a solution Sedimentary formations often have distinctive layers that show different conditions when they were laid down 14 3 Economic Geology and Mineralogy Economic mineralogy is the study of minerals that are valuable for manufacturing and are therefore an important part of domestic and international commerce Most economic minerals are metal bearing ores Nonmetallic economic minerals are mostly graphite some feldspars quartz crystals and diamonds Most economically valuable crustal resources exist everywhere is small amounts the important thing is to find them concentrated in economically recoverable levels Metals are essential to our economy Sand and gravel production comprise by far the greatest volume and dollar value of all nonmetal mineral resources and a far greater volume than all metal ores o Sand and gravel are used mainly in brick and concrete construction paving as lose road filler and for sandblasting o High purity silica sand is our source of glass Limestone like sand and gravel is mined and quarried for concrete and crushed for road rock Evaporites materials deposited by evaporation of chemical solutions are mined for halite gypsum and potash Sulfur deposits are mined mainly for sulfuric acid production 14 4 Environmental Effects of Resource Extraction The most obvious effect of mining is often the disturbance or removal of the land surface o Farther reaching effects include air and water pollution o Chemical and sediment runoff pollution is a major problem in many local o After use in ore processing most water contains sulfuric acid arsenic heavy metals watersheds and other contaminants o Mine runoff leaking into lakes and streams damages or destroys aquatic ecosystems Mining can have serious environmental impacts o The most common methods are open pit mining strip mining and underground mining Underground mining explode Mine tunnels occasionally collapse and natural