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EARTH’S COMPONENTS & CHARACTERISTICS UNIT 9 Environmental Geology APES GEOLOGIC TIME SCALE • Organizes Earth’s 4.6 billion years of history into subgroups • Subgroups: – Eons • Eras – Periods » Epochs • 4 Major Eons… 1. Hadean Eon • Oldest amount of time • 4.6-3.8 billion years ago • No rocks from this eon found on Earth • Evidence from meteorites & moon rocks 2. Archean Eon • 3.8-2.5 billion years ago • 3.8 BYA Oldest rocks on Earth • 3.5 BYA oldest fossils of cells (prokaryotes) • 2.7 BYA atmospheric O2 begins to rise 3. Proterozoic Eon • 2.5 billion – 543 million years ago. • 2.2 BYA oldest fossils eukaryotic cells • 600 MYA diverse algae & soft • Bodied invertes 4. Phanerozoic Eon • 543 million years- present • Paleozoic Era – 543-248 million years – Diverse land plants, amphibians, reptiles, insects (Cambrian Explosion) – Mass extinction due to glaciation (global cooling)killed 90% of species (end of Permian period) • Mesozoic Era – 248-66 million years – Age of Reptiles – Mass extinction due to climate change- 10-15% extinct (Cretaceous extinctions) • Cenozoic Era – 65 million years to present – Age of Mammals STRUCTURE OF THE EARTH • Planetary differentiation- as more dense materials sank to center of earth, less dense material rose to surface • Layers of Earth • Core- center, mostly iron – Inner core- 1220 km thick, T & P cause iron to solidify – Outer core- 3480 km thick, liquid iron, creates magnetic field • Mantle- 70% of earth’s interior, made of O, Si, Mg – Asthenospere- closest to core, gelatinous, where magma is formed – Upper mantle- cooler, more solid, brittle • Crust- outermost layer – Crust + upper mantle make up lithosphere Plate Tectonics • Tectonic plates- made of… – Uppermost mantle – Crust- 2 types: • Oceanic- thin (5-10 km), dense, rich in Fe, Mg, Si, below sea level • Continental- thick (20-70 km), less dense, rich in Ca, Na, K, Al • Constantly moving about 110 cm/year • 15 major plates- We are on North American Plate Plate Boundaries • Where 2 plates meet • 3 types of plate boundaries 1. Transform Boundaries • Plates slide past each other at transform faults • Movement is horizontal (strike-slip fault) – To the left- sinistral – To the right- dextral • Mostly smooth movement • If stuck, pressure builds, causes earthquakes 2. Convergent Boundaries • 2 plates move toward each other • 3 types: a. OCEANIC - CONTINENTAL • • • • • Oceanic plate is forced under continental plate Called subduction Creates deep-sea trench Creates volcanic mountains along continental plate. EX: Peru-Chile Trench and Andes Mountains of South America b. OCEANIC - OCEANIC • • • • • • Oceanic plate is forced under another oceanic plate Called subduction Crust melts into mantle Creates deep-sea trench Creates arc of volcanic islands that parallel trench EX: Mariana Trench & Mariana Islands Aleutian Trench & Aleutian Islands c.CONTINENTAL - CONTINENTAL • Two continental plates collide • Mountain ranges are created • EX: HimalayasIndian plate forced under Eurasian plate 3. Divergent Boundaries • 2 plates move apart • Creates rifts • Magma comes to surface & cools, creating crust • Usually in oceans, but can occur in continents (Africa’s Rift Valley) • Creates mid-ocean ridges • EX: Mid-Atlantic Ridge created when N.American plate pulls away from Eurasian plate. CAUSES OF PLATE MOVEMENT • Convection currents – Hot mantle rises – Cools down – Cooled-down mantle sinks – Creates currents that move plates. THEORY OF CONTINENTAL DRIFT • Alfred Wegner was first to propose theory of continental drift • He said: – All continents joined in large land mass called Pangea (Greek for “all land”) – Pangea began breaking up 200 million years ago. – Continents ended up where they are now – Continents are still moving Evidence of Continental Drift • Fossils- similar plants & animals on widely separated continents • Rock Formations- similar rock types & stratification between 2 continents • Climate- Antarctica has coal deposits, indicating it had swamps, thus warmer weather= closer to equator Geologic Hazards associated with Continental Drift • • • • Earthquakes Volcanoes Landslides Floods Earthquakes • Epicenter- point where first movement occurs • Damage depends on soil underneath • Modern contractors build weak spots, pads/floats to absorb vibration • Underwater earthquakes cause tsunamis – Destroy coastal ecosystems – Saltwater infiltrates soil – sewage/industrial waste infect freshwater supplies Volcanoes • Good – Created land (fertile soil), atmosphere, oceans • Bad – Release sulfur, combines with H20 to form sulfuric acid; interferes with solar radiation, cools climate (Mt. PinatuboPhilippines) – Dust/Ash- can change climate by blocking sunlight (1815- Mt. Tambora in Indonesia, snowed in July in parts of New England, “year without a summer”) – Clouds of hot, toxic gases – Mudslides Landslides • Mass wasting/movement • Usually slow & subtle, can happen all at once • Construction, forest clearing, agriculture, building on steep slopes increase frequency & damage Flooding • Excess water that overflows stream banks • Contaminates everythingvery costly • Pavement/buildingsspeeds rate of runoff, soil has no chance to absorb • Floodplains- fertile, attract people/agriculture, affected most by flooding • READ chapter 16 on Natural Disasters!!