ENV200 Chapter 12 Notes

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University of Toronto St. George
School of Environment
Romila Verma

CHAPTER 12 – ENVIRONMENTAL GEOLOGY AND EARTH RESOURCES [12.1] EARTH PROCESSES SHAPE OUR RESOURCES Earth is a dynamic planet and constantly changing structure ­ Earth is a layered sphere o Core = a dense, intensely hot mass of metal (e.g., mostly iron)  Solid in the inner core  Fluid in the outer core  Generates a magnetic field o Mantle = a hot, pliable layer of rock  Less dense than the core  Contains a high concentration of lighter elements (e.g., oxygen, silicon, magnesium) o Crust = a cool, lightweight, brittle layer of rock  Crust under oceans is relatively thin, dense, and young because of constant recycling  Mainly dense basaltic rock  Crust under continents is relatively thick, light, and old, with new material being added continually  Predominantly granitic rock Tectonic processes reshape continents and cause earthquakes ­ Tectonic plates = the huge convection currents in the mantle are thought to break the overlying crust into a mosaic of huge blocks o Sliding slowly across the earth's surface o Breaking up into smaller pieces o Pulling apart to open new ocean basins o Crashing into each other to create new, larger landmasses ­ Ocean basins form where continents crack and pull apart o Mid-ocean ridges = magma forced up through the cracks forms new oceanic crust that piles up under water  Magma = molten rock  Largest mountain range in the world  Higher peaks, deeper canyons, and sheerer cliffs than any continental mountains ­ Earthquakes are caused by jerking as plates grind past each other ­ Mountain ranges are pushed up at the margins of colliding continental plates ­ When an oceanic plate collides with a continental landmass, the continental plate usually rides up over the seafloor, while the oceanic plate is subducted (pushed down into the mantle) where it melts and rises back to the surface as magma o Subduction zones are marked by deep ocean trenches o Volcanoes are formed where magma erupts through vents and fissures in the overlying crust ­ Ring of fire = a ring of oceanic trenches and volcanic mountains o Formed where oceanic plates are being subducted under the continental plates o Source of more earthquakes and volcanic activity than any other region on the earth ­ Continents can drift long distances over millions of years o Most or all of the continents were gathered to form supercontinent(s), which have separated and re-combined repeatedly over hundreds of millions of years  Profound effects on the earth's climate  May explain the periodic mass extinctions of organisms between major geologic periods ­ Humans have now become a major geological force o We may cause more species extinction than any natural forces o Anthropocene era = dominated by humans [12.2] MINERALS AND ROCKS ­ Mineral = a naturally occurring, inorganic solid with a specific chemical composition and a specific internal crystal structure o Metals come from mineral ores, but once purified, metals are no longer considered minerals o Mineral crystals can be microscopically small or huge ­ Rock = a solid, cohesive aggregate of one or more minerals o Individual mineral crystals (or grains) are mixed together and held firmly in a solid mass  Each grain retains its own unique mineral qualities o Each rock type has a characteristic mixture of minerals, grain sizes, and ways in which the grains are mixed and held together  Granite = a mixture of quartz, feldspar, and mica crystals  Rhyolite = a granite-like mineral conten
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