Chapter Three: The Dynamic Earth I. Earth as a System: Some scientists divide the Earth into 4 main parts geosphere, atmosphere, hydrosphere, and

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1 Chapter Three: The Dynamic Earth I. Earth as a System: Some scientists divide the Earth into 4 main parts geosphere, atmosphere, hydrosphere, and biosphere. We will be taking an overview of these parts in this chapter. A. Discovering Earth s Interior 1. Geosphere: solid part of the Earth that consists of all rock and the soils and sediments on the Earth s surface; extends from the center of the Earth to its crust 2. Most of the geosphere is located in the Earth s interior, yet the deepest well that has been drilled is only about 12 km deep. 3. Scientists gather information about the Earth s interior by studying seismic waves. 4. Seismic waves are altered by the nature of the material through which they travel. a. By looking at the changes in speed and direction of seismic waves, scientists have learned that there are different layers making up the interior of the Earth and have inferred what the composition is of each of these layers. i. Crust: Earth s thin outer layer, made almost entirely of light elements ii. Mantle: underneath the crust; makes up most of Earth s mass; made of rocks of medium density iii. Core: center of the Earth, composed of the densest elements

2 5. By examining the physical properties of the geosphere, scientists have divided the Earth into 5 layers. Working from the surface of the Earth inward, they are: a. Lithosphere outer layer; cool and rigid; km thick; includes the crust and uppermost part of the mantle; made up of tectonic plates b. Asthenosphere plastic, solid layer of the mantle that is made of rock that flows very slowly, allowing the tectonic plates to move on top of it; 250 km thick c. Mesosphere lower layer of the mantle; middle sphere; 2,550 km thick d. Outer Core dense, liquid layer of nickel and iron; 2,200 km thick e. Inner Core a dense, solid sphere of mostly nickel and iron at the center of the Earth; temperature estimated between 4,000 C to 5,000 C; remains solid despite high temperature because of enormous pressure

3 6. Plate Tectonics a. Plates glide across the asthenosphere like ice in a pond. b. Major plates: Pacific, North American, South American, African, Eurasian, Antarctic c. At the plate boundaries, much geologic activity takes place. i. Plates can separate, collide, slip past one another; the huge forces and energy involved can lead to earthquakes or cause volcanoes to erupt.

4 ii. Where plates collide, the crust becomes thicker and eventually mountain ranges are formed. Major tectonic plates: 1. Pacific 5. South American 9. Australian 2. North American 6. African 10. Antarctic 3. Cocos 7. Eurasian 4. Nazca 8. Indian 7. Earthquakes a. Fault: break in the Earth s crust along which blocks of the crust slide relative to one another b. When rocks under stress suddenly break along a fault, ground vibrations are set off an earthquake.

5 c. Richter scale: quantifies the amount of energy released by an earthquake; known as its magnitude i. Smallest felt is about 2.0, largest recorded is 9.5 ii. Each whole number is an increase of 31.7 times more energy than the level below it. d. Majority of earthquakes take place at or near tectonic plate boundaries due to stresses caused by plates moving against one another. e. One of the most famous: San Andreas fault which runs the length of California f. Not all earthquakes happen along plate boundaries though Charleston, SC and Reading, PA have had earthquakes! 8. Volcanoes a. Volcanoes are mountains b. built from magma that rises from the Earth s interior to the surface. c. Often located near tectonic plates, specifically where plates are either colliding or separating from each other. d. They can occur both on land or under the sea (may break the surface of the sea as islands). e. Ring Of Fire: contains nearly 75% of the world s active land volcanoes; located along the tectonic plate boundaries surrounding the Pacific Ocean

6 f. Local effects of volcanoes immediate and total destruction of everything nearby; mudflows and ash are just as destructive g. Global effects: major eruptions can cause a change in climate for several years i. Clouds of ash and gas reach upper atmosphere and reduce the amount of sunlight reaching the planet consequently dropping the global temperature by several tenths of a degree Celsius over a period of several years ii. Mount St. Helens, Mount Pinatubo, Krakatoa Mount St. Helens - May 18, USGS 9. Erosion a. Earth s surface is constantly battered by the weather wind, water, etc. b. erosion generally, the removal and transport of surface material c. The forces of wind and water (influenced by local specifics of vegetation, soil composition, etc. ) do much to shape and carve the landscape of the Earth over long periods of time.

7 II. The Atmosphere One of the ways that the Earth is unique is its atmosphere. The role it plays is crucial to the Earth s ability to support life without this insulating blanket, Earth s temperature would fluctuate too greatly to support life as we know it. The existence of lots of liquid water in combination with our atmosphere allows Earth to stay at relatively stable temperatures. In addition, the protective ozone layer also allows life to exist by keeping out deadly UV rays from the sun. A. Composition of the Atmosphere 1. 78% nitrogen, 21% oxygen, and 1% other including argon, carbon dioxide, methane, and water vapor 2. Solids atmospheric dust mostly soil but also includes salt, ash (fires and volcanic), skin, hair, pollen, bacteria, viruses, etc. 3. air pressure: gravity pulls the atmosphere toward the Earth s surface, and so the atmosphere is more dense near the surface of the Earth almost the entire mass of the atmosphere is located within 30 km of the Earth s surface. B. Layers of the Atmosphere starting from closest to Earth s surface in order: Troposphere, Stratosphere, Mesosphere, Thermosphere 1. Troposphere: about 18 km thick, this is where almost all weather occurs; densest layer; temperature decreases as altitude increases

8 2. Stratosphere: from 18 km 50 km up; contains the ozone layer; many jets fly in lower portion of this layer; temperature rises as altitude increases due to ozone absorbing the sun s UV energy and warming the air 3. Mesosphere: from 50 km to 80 km up; coldest layer of the atmosphere 4. Thermosphere: 80 km and up; nitrogen and oxygen absorb solar radiation causing the thermosphere to be the hottest layer by far but there are so few air particles that heat transfer rarely occurs a. Ionosphere lower portion of the thermosphere, atoms here become electrically charged from absorbing solar radiation and sometimes radiate light energy - e.g. aurora borealis (Northern Lights) C. Energy in the Atmosphere: There are 3 ways to transfer energy from the sun radiation, conduction, and convection 1. radiation: the transfer of energy by electromagnetic waves such as visible light and infrared waves; across space and the atmosphere

9 2. conduction: flow of heat through matter from a warmer object to a colder object in direct contact with each other 3. convection: transfer of heat by fluid currents that are moving as a result of differences in density caused by temperature variations D. Heating of the Atmosphere 1. Our planet only receives about two-billionths of the energy released by the sun. 2. About half of the solar energy that enters the atmosphere passes through and reaches the Earth s surface. The rest is absorbed or reflected by clouds, gases, dust, or reflected by the Earth s surface. 3. Oceans and land radiate the energy they have absorbed back into the atmosphere. E. Movement of Energy in the Atmosphere 1. Air moving upward, downward, or sideways causes Earth s weather. 2. Currents of less dense air that has been warmed by Earth s surface travel upward into the atmosphere while currents of denser colder air travel down to the ground. 3. The rising warm air begins to cool and the sinking cold air begins to warm, causing them to change directions. 4. This circular pattern is called a convection current. F. The Greenhouse Effect 1. The gases in the atmosphere act like the glass in a greenhouse, trapping heat.

10 2. Sunlight heats the surface of the Earth, which radiates heat back to the atmosphere. 3. Some of this radiated heat escapes into space. 4. The remainder of the heat is absorbed by certain gases in the atmosphere (greenhouse gases like carbon dioxide and methane), which warms the air. 5. This heat is now radiated back to the surface of the Earth, raising the temperature. 6. Without the greenhouse effect, Earth would be too cold for life to exist as we know it. 7. However, the excess of greenhouse gases (namely carbon dioxide) has caused the temperature of the Earth to increase alarmingly over the last years. 8. The excess carbon dioxide is generally from human activity requiring the burning of fossil fuels. 9. This increase in the temperature of the Earth from the greenhouse effect is known as global warming, which is leading to overall climate change. The Greenhouse Effect Animation G. Changes in the Atmosphere Before life: mostly water vapor, CO2 and sulfur gases from erupting volcanoes First life: we re not completely sure, but they might have obtained energy from the chemicals in the ancient seas

11 1. Eventually, bacteria evolved that could combine H2O, CO2 and sunlight to get food (photosynthesis). 2. resulted in lots of oxygen gas being put into the atmosphere, making it possible for other forms of life to evolve H. Element Cycles 1. Cycles of oxygen, carbon dioxide, water vapor, and nitrogen moving from the atmosphere, through bodies of organisms, and back to the atmosphere have been going on for billions of years. 2. part of the carbon of the Earth is cycled, but most is stored in the bodies of organisms (alive and dead) 3. We will go into detail of many elemental cycles later in the course. I. Human impacts on the atmosphere: 1. increased greenhouse effect (climate change) 2. pollution 3. ozone depletion a success story! III. The Hydrosphere A. The hydrosphere includes all of the water on or near the Earth s surface such as oceans, lakes, polar ice caps, groundwater, and clouds % of the Earth s surface is covered by water a. 98% of the hydrosphere is salt water located mostly in the oceans (World Ocean)

12 b. 2% of the hydrosphere is fresh water; 2/3 of the fresh water is frozen in ice caps or glaciers 2. Most life forms on Earth are supported by fresh water, but there is very little available 3. 2 types of fresh water: surface & ground a. surface water includes lakes, streams, rain runoff b. ground water flows beneath the surface of the Earth through small spaces in and between rocks two main types i. confined or artesian aquifer: layer of waterbearing porous rock that is trapped between upper and lower layers of less permeable material (often clay); this rock holds water much the same way that a sponge does ii. the weight of the layers above it cause great pressure and water sometimes reaches the surface without additional pumping when a well is drilled into it iii. natural springs occur when there are cracks in the trapping layer above an artesian aquifer; water reaches the surface due to the pressure iv. unconfined aquifer: does not have an upper layer of less permeable rock above it

13 4. Temperature Regulation a. The world ocean has a huge role in regulating the temperature of the Earth. b. The ability for water, (especially a body of water as big as the world ocean), to absorb and store energy from sunlight has a huge impact in keeping the temperature of the Earth relatively steady. c. Over half the solar radiation that reaches the Earth s surface is absorbed by the world ocean, and energy is absorbed and released more slowly by water than by land. d. Without the world ocean, the temperatures on Earth would be too extreme for life to exist. B. Changes in the Hydrosphere: The shape and location of the Earth s oceans have changed over time; some changes are slow, some happen in cycles 1. ice ages: long periods of cooling during which glaciers move from the poles to cover much of the Earth s surface After an ice age, glaciers retreat back to the poles. a. have been at least 5 major ice ages in the Earth s history b. most recent ice age ended 10 12,000 years ago 2. Movement of Glaciers: a. large scale weathering and erosion

14 b. relocation of huge rocks and other materials c. most recent ice age effects: i. Great Lakes ii. Cape Cod peninsula 3. Cause of ice ages is unknown, but many hypotheses exist wobbling of Earth on its axis 4. El Nino occurs when the annual December current of warm, nutrient poor water lasts several months instead of the normal few weeks; this current flows along the coast of South America a. Effects of El Nino i. Global weather patterns are disrupted moisture is relocated from usual areas resulting in some areas getting so much that flooding is a problem and other areas becoming too dry to support plant life; crop yields can be greatly impacted ii. changes in water temperature and nutrients cause fish populations to decrease and some populations relocate to colder, deeper, nutrient rich waters; disrupts the food chain and causes impacts on birds, mammals, other fish iii. fishing industry suffers from the lack of fish available

15 iv. poultry and egg industries are impacted as well (use fish meal) b. We are getting better at predicting the arrival of El Nino; particularly bad years: 1982, 1998 c. El Nino is often followed by La Nina, which can have opposite effects of El Nino (cold water this time instead of warm) No one is sure of the cause of El Nino, but it usually runs in cycles, happening every 2 to 7 years. National Geographic - El Nino IV. The Biosphere A. Composed of the parts of the Earth that support life, it s a narrow layer around the Earth. A commonly used comparison: if the Earth is an apple, then the biosphere is the skin of the apple. 1. only about 20 km thick, ( about 11 km into the ocean and 9 km into the atmosphere) 2. most organisms live in a narrower range, about 500m below the surface of the ocean to about 6 km above sea level 3. Reasons for narrower range: a. pressure is too high deep below ocean surface b. oxygen is too thin and temperatures are too low in higher altitudes

16 The Water Cycle I. Water cycle (aka Hydrologic Cycle) the continuous movement of water from the ocean to the atmosphere to the land and back to the ocean A. Evaporation is a key process in the water cycle. Liquid water is heated by the sun and rises into the atmosphere as water vapor. This happens continuously from the oceans, lakes, streams, and soil with the greatest portion being from the oceans. 1. Heat and wind increase the rate of evaporation. 2. Exposed soil (such as from logging, farming, or buildings) loses water much faster than a similar area with natural vegetation. 3. Water also enters the atmosphere through transpiration (which is the evaporation of water from leaves of plants). 4. The processes of evaporation and transpiration distill water and minerals and pollutants are filtered out. 5. Cellular respiration and combustion also add water to the atmosphere but in small amounts. B. Water from the atmosphere returns to the Earth in the form of precipitation, which occurs when the water vapor condenses to form a liquid. 1. Water particles usually condense around dust particles which then collide and stick together to

17 form the water droplets that fall as rain, snow, sleet, or hail. 2. Part of the precipitation can be used by plants and animals, but much of it flows as runoff into surface water such as rivers, lakes, and oceans. 3. Some precipitation and surface water soaks down through the soil to recharge aquifers and other groundwater. a. The area of the Earth s surface where water percolates down into an aquifer is called the recharge zone. b. If an area is covered with impermeable materials, it cannot recharge the aquifer (e.g. buildings, parking lots). c. Water table the upper limit of groundwater held in an aquifer; rocks and soil are saturated d. May take hundreds or even thousands of years to fully recharge an aquifer; sometimes they never recharge completely. C. Human Impacts 1. Clearing plants from the surface of the Earth increases runoff, erosion, evaporation, and reduces transpiration. 2. Watering plants on farm fields places significant stress on surface and groundwater sources, sometimes depleting them, and it increases evaporation.

18 3. Atmospheric pollution can result in acid rain and we also pollute water directly (sewage, chemicals, etc.). 4. Our unrestrained use of water for irrigation and industry is so great that we are depleting groundwater at an alarming rate. In some areas of the world, (South Asia, American West, Middle East) water shortages are leading to many conflicts.

19 Biogeochemical Cycles Note: Nutrients circulate throughout the environment in cycles called biogeochemical cycles, or nutrient cycles. Nutrients that cycle through all of Earth s spheres and organisms include carbon, oxygen, phosphorus, and nitrogen. The water cycle plays parts in all of the biogeochemical cycles. I. The Carbon Cycle: A. At the heart of the carbon cycle are photosynthesis and cellular respiration. 1. Photosynthesis (as performed by producers) involves converting the carbon dioxide in the atmosphere into carbohydrates (glucose). 2. Consumers eat the producers (or other organisms that ate the producers) and obtain the carbon from the carbohydrates. 3. Through cellular respiration, the carbohydrates are broken down into usable energy and carbon dioxide is released back into the atmosphere. Both producers and consumers use cellular respiration. B. Sediments 1. Organism remains in water may settle into sediments. As layers accumulate, pressure increases and the soft tissues can get converted into fossil fuels. Harder parts, such as shells and skeletons, are converted into sedimentary rock.

20 a. Limestone and other sedimentary rock make up the largest reservoir of carbon. b. Some of this carbon is released through erosion and volcanic eruptions. 2. When fossil fuels are burned, carbon is released. C. Oceans 1. Oceans absorb carbon compounds from the atmosphere, runoff, undersea volcanoes, and from the wastes and remains of organisms. 2. Water temperature and the number of marine organisms influence the rates at which carbon is released and absorbed. 3. Oceans are the second largest carbon reservoir. D. Human Impacts 1. Carbon is shifted by human activities : extraction of fossil fuels removes carbon from storage in the lithosphere and burning them releases carbon into the atmosphere. 2. The cutting and burning of forests also contributes to the carbon in the atmosphere. The loss of vegetation means there are fewer plants to absorb carbon dioxide out of the atmosphere. E. More to Learn 1. We don t completely understand the carbon cycle. 2. There is a missing carbon sink (or reservoir) that scientists have yet to identify.

21 3. Of the CO2 released by humans, more 1-2 billion metric tons are unaccounted for. Many scientists think it is absorbed by the northern forests but we don t know for sure.

22 II. The Nitrogen Cycle A. Even though nitrogen gas makes up 78% of the atmosphere, as a gas it cannot cycle out of the atmosphere and into most organisms directly. 1. The result is that nitrogen is relatively scarce in the lithosphere, hydrosphere, and organisms; a lack of nitrogen often limits plant growth. 2. Once nitrogen undergoes the right kind of chemical change, (through lightning, specialized bacteria, or human technology), it becomes usable by the organisms that need it. These compounds are highly effective fertilizers in the biosphere. B. Nitrogen Fixation 1. Nitrogen fixation: the conversion of nitrogen gas (N2) into ammonia (NH3) a. Two naturally occurring ways to do this: i. intense energy of a lightning strike ii. when air in the top layer of soil comes in contact with certain bacteria called nitrogen-fixing bacteria b. nitrogen-fixing bacteria live freely in soil or in root nodules of certain plants (called legumes) i. legumes include soybeans, peas, beans, clover, alfalfa, peanuts and others ii. farmers often plant legumes to return nitrogen to the soil

23 C. Nitrification and Denitrification 1. Other types of bacteria use ammonia ions (from either nitrogen fixation or from the wastes of decomposers) to perform nitrification 2. Nitrification: conversion of ammonia ions (NH4 + ) into nitrite ions (NO2 ) and then into nitrate ions (NO3 ) 3. Plants can take up nitrate ions, providing the nitrogen needed for proteins, DNA, RNA and other important molecules. Consumers get their nitrogen from eating the plants or other organisms. 4. Completion of the cycle occurs when denitrifying bacteria convert nitrates in soil or water back to nitrogen gas. D. Human Impacts 1. As mentioned, humans can fix nitrogen. The process to synthesize ammonia was developed shortly before World War I and later improved upon to increase production on a larger scale. 2. Now the limitations on plant growth imposed by a lack of nitrogen in the biosphere could be overcome. 3. Humans fix at least as much nitrogen as that which is fixed naturally.

24 a. This increases the flow of nitrogen out of the atmosphere and into other reservoirs of nitrogen. b. Other activities change the flow of nitrogen as well: i. Burning of forests and fields forces nitrogen out of the plants and into the atmosphere ii. Burning of fossil fuels increases the rate at which nitric oxide (NO) enters the atmosphere and forms nitrogen dioxide (NO 2 ), which can lead to acid rain.

25 III. The Phosphorus Cycle A. Phosphorus is needed by organisms for cell membranes, DNA, RNA, and many other essential molecules. But the amount of phosphorus located in organisms is incredibly small compared to the vast amounts contained in rocks, soil, sediments, and the oceans. 1. Phosphorus is only released naturally when rocks are worn down by water or wind. 2. Locked in rock, most phosphorus is unavailable to organisms and so scarcity of phosphorus limits plant growth. 3. When phosphorus is artificially added, plant and algal growth increase significantly. B. The Phosphorus Cycle 1. Plants can only take up phosphorus in their roots when it is dissolved in water. 2. Consumers get the phosphorus they need from the water they drink and the organisms they eat. 3. Decomposers return phosphorus to the soil by breaking down the wastes and bodies of consumers.

26 Phosphorus Cycle: the phosphorus cycle describes the routes that phosphorus atoms take through the environment. In this diagram, labels in boxes refer to reservoirs of phosphorus, and italic labels refer to processes of the phosphorus cycle. C. Human Impacts 1. Phosphorus is mined from the Earth to use as fertilizer. 2. Wastewater from homes and businesses tends to be rich in phosphorus, partly because of the phosphorus contained in most detergents. When this wastewater enters bodies of water from leaching or runoff, it can lead to eutrophication. 3. Eutrophication: an increase in the amount of nutrients (especially nitrates and phosphorus) in an aquatic ecosystem; can occur naturally or artificially (fertilizer runoff, sewage discharge)

27 a. The increase in nutrients typically leads to an overgrowth of producers (usually algae). b. As the algae die and decompose, oxygen is depleted from the water by the decomposers. The lack of oxygen can lead to the death of many aquatic animals if they are not able to flee the area. c. Hypoxia: condition where dissolved oxygen levels fall below what is needed to support most animal life; generally below 2 ppm 4. Case in Point: Gulf of Mexico Dead Zone a. Excess nitrogen and phosphorus from fertilizer runoff and other human activities flow into the Mississippi River and are released into the Gulf of Mexico. b. The consequent algal bloom and hypoxia creates a huge dead zone every year that has been increasing in size. c. How do you fix the problem when the economic livelihood of some states result in an economic downturn for others? CBS News Dead Zone

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