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Earth Systems and Resources 10-15 % of your APES Exam Geologic Time • Based on layering of rocks and evolution of life • Also based on radiometric dating • Eon-> Era-> Period-> Epoch-> Stages Geologic Time • Rock Layers (strata) are laid down in succession with each strata representing a “slice” of time • The principle of superposition- any given stratum is probably older than those above it and younger than those below it. Geologic Time Scale • Several factors complicate things… – Sequences of strata are often eroded, distorted, tilted or inverted after deposition – Strata laid down at the same time but in different places can have different appearances – Strata of any given area can represent only part of Earth’s history. Earth’s Structure • Formed 4.6 billion years ago • Includes – Biosphere- all life on earth – Hydrosphere- all water on earth – Internal structures… Crust • Crust makes up 0.5% of Earth’s mass • Ocean- basalt (contains minerals rich in heavier elements such as Iron, relatively uniform) • Continental- granite (much thicker composed of volcanic, sedimentary and metamorphic rock- very stratified) The Rock Cycle • Igneous- Formed by cooling and classified by silica content. Intrusive igneous rocks solidify deep underground and cool slowly and have a large grained texture (granite) Extrusive igneous rocks solidify on and near the surface and have a small grained texture (basalt) • Metamorphic- formed by intense heat and pressure. Ex: Diamonds, Marble, Asbestos, Slate, Coal • Sedimentary: formed by piling and cementing of various minerals overtime in low-lying areas. Fossils form ONLY in sedimentary rocks Rock Cycle MOHO, Mantle and Core • Mohorovicic Discontinuity- boundary between the crust and mantle. • Mantle- composed of iron, magnesium, aluminum and silicon-oxygen compounds. Upper third is the plastic asthenosphere • Core- composed of iron- Inner core is solid Plate Tectonics • Theory of plate tectonics comes from 2 observations: continental drift and seafloor spreading The Continental Drift Theory • In 1915, Wegener proposed that continents came from one giant land mass (Pangea). Based his theory on 5 factors • 1. Fossilized tropical plants discovered beneath Greenland’s Ice caps • 2. Glaciated landscapes occurred in the tropics of Africa and South America • 3. Tropical regions on some continents had polar climates in the past, based on paleoclimatic data. • 4. Continents fit together like a puzzle • 5. Similarities existed in rocks between east coasts of N and S America and west coasts of Africa and Europe. Seafloor Spreading Theory • In the 60’s alternating patterns of magnetic properties were discovered in the rocks on the sea floor on either side of mid-oceanic ridges. • Dating the rocks indicates that rocks got older the farther away from the ridge. This suggests that new ocean floor was being made at the volcanic rift zones Transform Boundaries • Occur when plates slide past each other • This friction and stress build up causes earthquakes • Example: San Andreas Fault in California Divergent Boundaries • 2 plates slide apart from each other with the space created filled in with molten lava • Create massive fault zones in oceanic ridge system and areas of frequent oceanic earthquakes • Examples: Mid-Atlantic Ridge and East Pacific Rise in the ocean. East African Great Rift Valley in the continents. Convergent Boundaries • 2 plates slide toward each other commonly forming a subduction zone (one plate moving under the other, usually the more dense ocean plate goes under the continental plate). • Or they form a orogonic belt if the 2 plates collide and compress. • Examples: Cascade Mountains Convergent Boundaries • When 2 ocean plates collide they create and island arc- a curved chain of volcanic islands rising from the deep sea floor and near a continent. The curve is usually convex toward the open ocean. • A deep undersea trench is located in front of such arcs. • Example: Japan and Aleutian Islands in Alaska Convergent Boundaries • When 2 continental plates collide mountain ranges are made because crust is condenses and pushed upward. • Example: northern margins of the Indian subcontinental plate being thrust under a portion of the Eurasian plate, lifting it and creating the Himalayas. Earthquakes • Occur during abrupt movement on an existing fault along a tectonic plate boundary zone or along mid-oceanic ridges. • Massive amounts of stored energy are released in a short period of time. • The area where the energy is released is called the focus • The area directly above the focus is called the epicenter • The strength/magnitude of an earthquake is measured on the Richter scale Earthquake Case Studies • Haiti, 2010 – January 2010- Magnitude 7.0 Earthquake occurred at a depth of about 8 miles. – International Red Cross estimates that about 3 million people were effected. 200,000 killed. 250,000 injured. – Quake happened at the northern boundary of Caribbean tectonic plate Earthquake Case Study • San Andreas Fault – Transcontinental fault that extends 800 miles – Pacific Plate and North American Plates – Slippage is about 1.5 inches per year – 1906 earthquake occurred near San Francisco (7.8) causing 3,000 deaths. Tsunamis • Series of waves created when a body of water is rapidly displaced usually by an earthquake • Subduction zone tsunamis are most common • Small wave-height and very long wave length off shore- don’t notice them at sea • In 2004 the Indian Ocean, 9.3 earthquake created a tsunami that killed about 300,000 people- said to be one of the deadliest natural disasters in history. Volcanoes • 95% occur at subduction zones and midoceanic ridges • 5% occur at hotspots where plumes of magma come close to the surface. • Volcanoes produce ejects (lava rock and/or ash), molten lave and toxic gas Volcanoes • Affect the climate by introducing large quantities of Sulfur Dioxide that is converted to sulfate ions in the atmosphere. • These particles reflect shorter wave lengths of solar radiation and serve as condensation nuclei for high clouds • Mt. Pinatubo erupted in 1992 and decreased average global temperature 1 F because of the sulfate particles in the stratosphere • Particles take about 2 years to settle out and are a big cause of acid rain. Volcanoes • How to deal – Modeling and data analysis for better volcanic activity prediction – Better evacuation plans – Study of precursors such and changes in the cone – Measuring changes in temperature and gas composition – Magnetic changes – Changes in seismic activity (correlation between seismic and volcanic activity) Volcano Case Study • Mount Saint Helens: – Located in Washington State- erupted in 1980 removing trees and increasing soil erosion. – Destroyed wildlife, polluted air with gases and ash – Increases mudflows and melting of glacial ice and snow – Clogged rivers that created flooding problems – 57 people killed Volcano Case Study • Mount Pinatubo – Part of a chain of volcanoes on the west coast of the island of Luzon ins the Philippines. – In June 1991 it erupted for 9 hours and vented 18 million metric tons of sulfur dioxide into the atmosphere which encircled Earth in 3 weeks after reaching the stratosphere. Largest sulfur dioxide cloud ever detected to date. – Sulfate aerosols formed in the stratosphere increased reflection of solar radiation and within 3 years caused an overall 2 F cooling of the earth. Seasons, Solar Intensity and Latitude • Factors that affect amount of solar energy at earths surface – Earth’s Rotation (once every 24 hours) – Earth’s Revolutions around the sun (once every 365ish days) – Tilt of Earth’s Axis (23.5 degrees) – Atmospheric conditions Seasons, Solar Intensity and Latitude • Summer in the Northern Hemisphere occurs when the Northern Hemisphere is tilted toward the sun. • Winter in the Northern Hemisphere is actually when the Earth is Closest to the sun • Seasons are NOT caused by distance of the earth to the sun Soil • Composed of – Minerals of different sizes – Organic Materials from remaining dead organisms – Open space that can be filled with air or water • Good Soil should have about 45% minerals (sand, silt and Clay) 5% organic matter, 25% air and 25% water Soil Development • 1. Parent Material – this refers to the rocks and minerals from which the soil derives. The nature of the parent rock, which can be native to the area or transferred in by wind, water or glacier has a direct effect on the ultimate soil profile • 2. Climate. This is measured by precipitation and temperature. It results in partial weathering of the parent material which forms the substrate for soil. Soil Development • 3. Living Organisms: These include the nitrogen-fixing bacteria Rhizobium, fungi, insects, worms, snails, etc. that help to decompose litter and recycle nutrients. • 4. Topography: This refers the physical characteristics of the location where the soil is formed. Topographic factors that affect a soil’s profile include, drainage, slope direction, elevation and wind exposure. Soil • With sufficient time, a mature soil profile reaches a state of equilibrium. Feedback mechanisms involving both abiotic and biotic factors work to preserve the mature soil profile. The relative abundance of sand , silt and clay is called the soil texture. Soil Triangle Soil Profile Organic Vs. Inorganic Fertilizer • Organic – 3 common forms: animal manure, green manure, compost – Improves soil texture, adds organic nitrogen, stimulates beneficial bacteria and fungi – Helps to prevent erosion • Inorganic • Does not add Humus to the soil resulting in less ability to hold water and support living organisms • Lowers oxygen content of the soil thereby keeping fertilizer from being taken up efficiently • Supplies only a limited number of nutrients usually only Nitrogen and Phosphorus • Requires large amounts of energy to produce, transport and apply • Releases nitrous Oxide N2O- a greenhouse gas Soil Erosion • Movement of weathered rock/soil from one place to another. • Caused by flowing water, wind, human activity • Soil Erosion destroys the soil profile, decreases the water-holding capacity and compacts the soil. • Because water cant percolate through the soil it runs off the land, taking more soil with it (positive feedback loop) • Leads to damage in agricultures, waterways (canals), infrastructure (dams). Interferes with wetland ecosystems, reproductive cycles (as in salmon), oxygen capacity and pH. Agriculture techniques that lead to soil erosion • • • • • Monoculture Row cropping Over grazing Improper plowing of soil Removing crop wastes instead of re-plowing them into the ground Types Of Soil Erosion • Sheet Erosion- soil moves off as a horizontal layer • Rill Erosion- fast-flowing water cuts small channels in soil • Gully Erosion- Extreme case of rill erosion where over time channels increase in size and depth. Desertification Salinization Waterlogging Definition Productive potential of arid or semiarid land falls by at least 10% due to human activity and/or climate change Water that is nor absorbed into the soil and evaporates leaves behind dissolved salts in topsoil. Saturation of soil with water resulting in a rise in the water table Symptoms Loss of native vegetation; increases wind erosion; salinization; drop in water table; reduced surface water supply Stunted crop growth; lower yield; eventual destruction of plants Saline water envelops deep roots killing plants; lowers productivity; eventual destruction of plant life Remediation Reduce overgrazing, deforestation, destructive forms of planting, irrigation and mining. Plant trees and grasses to hold soil Take land out of production for 2-5 years. Install drainage pipes. Plant salt loving plants (barley, cotton) flush with fresh water. Switch to less waterdemanding plants. Utilize conservationtillage farming, plant plants with deep roots, take land out of production, install pumping stations Soil Erosion Case Study • Dust Bowl – 1930s in Oklahoma, Texas and Kansas – Caused by plowing the prairies and resulted in loss of natural grasses that rooted the soil. – Drought and winds that occurred, blew most of the topsoil away – Caused people to leave the area Soil Laws • 1935 Soil Erosion Act: Established the Soil Conservation Service. Mandates the protection of the nation’s soil reserves. Deals with soil erosion problems, carries out soil surveys and does research on soil salinity. Provides computer databases for scientific research. • 1977 Soil and Water Conservation Act: Provides for a continuing appraisal of US soil water and related resources, including fish and wildlife habitats and a soil and water conservation program to assist landowners and land users in furthering soil and water conservation