6th Grade SI Notes Earth Systems: Structures and Processes Unit 6.E.2

Structure of the EarthThe Earth can be divided into different layers based on either composition or based on their different physical properties .Density and temperature both increase for deeper layers of the Earth.

Three-fourths of the Earth's surface is covered by a thin layer of water, and the entire Earth is surrounded by a thin layer of air, which consists partly of oxygen gas.However, Earth is composed primarily of rock. This rocky material can be divided, or classified, into layers based on the composition of the material that makes up the layers or the properties of the materials.

Classification of Earth's LayersThe diagram below shows two ways to classify Earth's layers. One way, shown on the left, is based on composition (what the layers are made of). The other way, shown on the right, is based on physical properties of the layers (solid vs. liquid, rigid vs. soft, etc.). In most cases, the boundaries between the physical layers do not line up with the boundaries of the compositional layers.

Earth's Compositional LayersEarth's compositional layers, from the outside to the center, are the crust, the mantle, and the core.

The crust is the outermost, thinnest, least dense layer. Continental crust is made mostly of the rock granite and is thicker and less dense than oceanic crust. Oceanic crust is made mostly of the rock basalt. Overall, crustal rocks are rich in the elements silicon (Si) and oxygen (O).

This cross section shows that continental crust (grey area labeled as "1") is thicker than oceanic crust (black area labeled as "2"). The

portion of the diagram labeled as "3" is part of the mantle. The blue area is ocean water.

The mantle is the hot, middle, thickest layer and accounts for most of the Earth's bulk. It is denser than the crust, but not as dense as the core. The density of the mantle increases with depth due to increasing pressure. Mantle rocks are richer in iron (Fe) and magnesium (Mg) than crustal rocks. Diamonds form in the high pressure conditions of the mantle.The core lies at Earth's center. The core is made mostly of iron and nickel, and it is the hottest, densest layer.

Earth's Physical LayersEarth's physical layers, from the outside to the center, are the lithosphere, the asthenosphere, the mesosphere, the outer core, and the inner core.

The lithosphere is the cold, brittle layer at Earth's surface. It is a solid layer that contains all of the crust and a very thin part of the mantle's top. Overall, the lithosphere is a rigid layer that is broken into large pieces called tectonic plates or lithospheric plates. These plates move around on top of the less rigid layer below them.The asthenosphere is a less rigid layer directly underneath the lithosphere. It consists entirely of mantle rock. Although it is solid, the asthenosphere is able to flow very slowly. This causes the rigid plates of the lithosphere on top to move around at rates of a few centimeters per year in response to movement in the mantle.The mesosphere is a solid layer that accounts for the rest of the mantle below the asthenosphere. The mesosphere is stronger and denser than the asthenosphere.The outer core is the liquid, outer portion of the Earth's core. The slow, gradual flow in the outer core produces the Earth's magnetic field.The inner core is the solid, inner portion of the Earth's core.

Earth's Magnetic FieldThe Earth has a global magnetic field which deflects harmful solar radiation.

Earth's Magnetic FieldThe Earth's core contains charged iron particles, and the Earth spins at a relatively rapid rate (once every 24 hours). These two characteristics create a dynamo effect and cause the planet to generate a relatively strong magnetic field, which is sometimes called the magnetosphere.The Earth's magnetic field helps to shield the planet from harmful particles emitted by the Sun. In addition to light, the Sun emits large amounts of charged particles, such as protons and electrons, known as the solar wind. Many of the charged particles that make up the solar wind are deflected once they encounter the Earth's magnetic field. Without this protection, the solar wind could strip the Earth of its atmosphere.

The Earth's magnetic field deflects the harmful particles of the solar wind.

The Earth Is Similar to Other MagnetsThe Earth has a global magnetic field that operates in a very similar way to those of smaller, handheld magnets. In general, the Earth can be thought of as having a giant bar magnet running through it, as shown in the image below.

Like human-made and other natural magnets, the Earth has two oppositely charged magnetic poles. These magnetic poles lie near Earth's North and South Poles.

Lithospheric Plate MovementLithospheric plate movement provides an explanation for the past, present, and future arrangements of the continents. It also explains the mechanism behind geologic phenomena, such as earthquakes, volcanic activity, and mountain building.

OverviewScientific evidence suggests that all seven of the continents on Earth today used to be connected, forming a single landmass called Pangaea. The theory that explains the breakup of this supercontinent and the movement of continents away from their placements within Pangaea is called plate tectonics. The term plate refers to large rigid blocks of the Earth's lithosphere (crust plus uppermost mantle), which move and interact with one another. Tectonics comes from the Greek root "to build".According to the theory of plate tectonics, the Earth's lithosphere is divided into a dozen or more large and small plates, as shown in the diagram below.

These plates are in constant motion because they are floating on a slowly flowing part of the upper mantle called the asthenosphere. The plates typically move a few centimeters per year. Large-scale change in the location of lithospheric plates generally takes place only over millions of years.

When the plates move, the continents and ocean floor, which are part of the plates, move as well. Ocean floors are the tops of thin oceanic plates that spread outward from

mid-ocean rift zones. Land surfaces are the tops of thicker, less-dense continental plates. At the places where two plates meet, constructive or destructive processes may take place. Some of those processes are discussed below.

Sea-floor Spreading

During the process of seafloor spreading, hot rock rises up from the mantle and forces its way to the surface to form new sections of oceanic crust at a mid-ocean ridge. The new crust pushes the older crust away from the mid-ocean rift zone, causing the seafloor to spread. This causes the ocean basin to widen and the continents to move away from each other.

Mountain FormationPlates move very slowly from a human's perspective—at rates of centimeters per year. Over time, however, these plate movements cause great changes to the Earth. For example, where continental plates collide, the crust tends to buckle and be pushed upward to form folded mountain ranges.

Volcano FormationAt some lithospheric plate boundaries, an oceanic plate plunges beneath another plate and sinks into the Earth's interior. As it sinks, it releases water, which rises into the overriding plate. This causes parts of the overriding plate to melt and form magma. The magma rises up, squeezing through widening cracks. Sometimes the magma reaches the surface and erupts as lava and ash. These erupting materials can build up over time to form volcanoes. Most volcanoes form in this manner near lithospheric plate boundaries, but they form in other areas as well.

EarthquakesEarthquakes occur along faults. Faults are cracks in bodies of rock along the division between two lithospheric plates. Some of the different ways in which rocks may move along a fault are shown below.

Rocks do not constantly move along a fault, though. Most of the time, the rocks on either side of the fault are locked together by friction. However, the pressure of the two lithospheric plates pushing against one another gradually builds. When the forces have built up enough to overcome the friction, the rocks suddenly slip past each other, releasing built-up energy as an earthquake. Lithospheric plate boundaries are made up of large, interconnecting faults, which are the sites of most earthquakes.

Folding & FaultingThe Earth's crust is divided into large sections calledlithospheric plates. These plates move very slowly over time.This movement causes stress in some parts of the crust, especially at the boundaries where two different plates are touching each other. At these places, faulting and folding can occur.

FaultingWhen extreme stress and pressure cause rock to fracture, or break, it is called afault. This break will occur along weak spots in the rock. Faults are the result of either compressional (pushing) or tensional (pulling) stress. Faults are most common at the borders of the lithospheric plates, but faults can occur anywhere that stress builds up in the rocks.The stress along a fault is released when the pieces of crust move. The rocks rubbing together can cause an earthquake. For this reason, earthquakes are more common at the boundaries between the different lithospheric plates.Faulting

When the rock layers break and move along a fault, the two sides of the fault can shift vertically, horizontally, or both. When the land shifts upward or downward (vertically) along a fault, valleys and mountain ridges can be formed. When it shifts parallel to the ground (horizontally), then the moving rocks can shift terrain and change the path of streams and runoff.

FoldingStress and pressure do not always break rocks. Sometimes the pressure in the Earth shifts the layers of rock upward or downward through folding. Large areas of folding may form valleys or mountains.Folding

EarthquakesSeismologists have studied how wave energy travels through different layers of Earth. During an earthquake, energy is released into the Earth as primary waves, secondary waves, and surface waves.

Cause of EarthquakesForces applied to one lithospheric plate by another cause stress on the rocks that compose the Earth's crust. Compressional stress is applied where rocks push together. Tensional stress is applied where rocks pull away from each other. Shear stress is applied where rocks move horizontally alongside each other.Over time, as more stress is applied, the rocks bend and begin to build up stored energy. If more stress is applied than the rocks can withstand, they will break or slip along a fault, releasing the built-up energy. The energy is released asearthquake waves.Earthquake waves travel outward in all directions from the earthquake's underground origin, or its focus. The point on the Earth's surface directly above the focus is the earthquake's epicenter.

Earthquake WavesThere are three basic types of earthquake waves, or seismic waves—primary waves, secondary waves, and surface waves.Primary (P) waves are the fastest type of seismic wave and originate at the earthquake focus. These waves travel directly through solids and liquids in the Earth's interior. P waves are longitudinal. Therefore, as P waves travel through matter, the particles of matter move back and forth along the direction of wave travel.Secondary (S) waves are the second fastest type of seismic wave and, like P waves, originate at the earthquake focus. S waves travel directly through the Earth's interior like P waves, but S waves can travel only through solids. As S waves travel through particles, the particles move back and forth perpendicular to the direction of wave travel. S waves are a type of transverse wave.

Surface waves are the slowest type of seismic wave but also the most destructive. These waves form when P waves or S waves reach the surface.There are several different kinds of surface waves that cause the ground to move in different ways. But all surface waves travel along the Earth's surface. Surface wave energy is always strongest at the earthquake epicenter. Surface waves often do the most damage of all the types of waves.

Applications of Seismic WavesScientists study and use seismic waves in many ways. The differences between P waves and S waves have allowed scientists to determine the structure of Earth's interior. For example, there is a certain zone through which S waves will not travel through the Earth. This is because S waves cannot travel through fluids. By carefully mapping out this zone, scientists have determined that the Earth's outer core is made of liquid.

S waves from an earthquake cannot pass through the Earth's core, which creates an S-wave "shadow zone" on the other side of the planet

from the earthquake's epicenter. Because of this shadow zone, scientists know that part of the Earth's core must be liquid (i.e. S-waves

cannot travel through liquids). Also, P waves that travel through the Earth's core are refracted (bent) in patterns that result in P-wave

shadow zones. Based on the refraction patterns, scientists have determined that the outer part of the core is liquid, while the inner core is

solid.

Scientists also use seismic waves to map locations of earthquake epicenters. Scientists measure seismic waves on instruments called seismographs. The arrival time and intensity of each kind of seismic wave is recorded by the seismograph onto readings called seismograms. By measuring the difference in arrival times of P and S waves at several seismograph stations, scientists can use triangulation to pinpoint the earthquake's epicenter. Only three seismograph stations are needed to locate an epicenter, but using more stations increases location accuracy.

The small red dots in this image are locations of seismograph stations. The red circles around each station represent the distance from the

station to an earthquake epicenter based on differences in arrival times between P waves and S waves. The location where all three circles

intersect each other (large red dot) is the location of the earthquake's epicenter.

Rock Formation & ClassificationThe rock cycle is the series of processes by which rocks are transformed from one type to another and continually renewed.On the basis of how a rock forms, it can be classified as one of three types: igneous rock, metamorphic rock, andsedimentary rock.

The Rock CycleThe origin of all rock can be ultimately traced back to the solidification of magma. Magma is a hot liquid made of melted minerals and compounds commonly found in rocks.

The rock cycle is a model that describes how rocks are created, changed, and broken down. There are three major types of rock: igneous rock, metamorphic rock, and sedimentary rock. During the rock cycle, each type of rock may be changed into another type.The rock cycle also includes several different processes. Crystallization is the process by which magma cools and forms solid rock. Heat and pressure often change one type of rock into another. Weathering, erosion, and deposition are the processes that break rock down into sediment at the Earth's surface. Wind, rain, running water, and ice commonly take part is these processes. Compaction and cementation—also known as lithification—is the process of loose sediments being formed into sedimentary rocks. And melting, of course, is the process that transforms solid rock back into liquid magma.The rock cycle is a process that takes hundreds of millions of years. But since it has operated continuously during Earth's history, new rock at the Earth's surface is constantly replacing old rock. This can happen when one continental plate slides under another in the process called subduction, and the material that was on the surface of the Earth is returned to the interior. In this way, old rock is recycled into new rock.

Igneous RockIgneous rock forms when magma and lava cool and make mineral crystals. Igneous rock is typically hard and is often glossy or shiny. Examples of igneous rock include granite, basalt, pumice, and obsidian. There are two basic types of igneous rock, which are classified by how they form: intrusive and extrusive. Intrusive igneous rock forms underground, within the Earth's crust or mantle, where magma

cools slowly. Because it cools slowly, intrusive igneous rock typically has large mineral crystals. 

Granite is a common type of intrusive igneous rock. The relatively large mineral crystals are easy to see with the naked eye.

Extrusive igneous rock forms above ground, as lava and other materials that erupt from volcanoes cool quickly. Because they cool quickly, extrusive igneous rocks have small

mineral crystals. 

Basalt is a common type of extrusive igneous rock. Individual mineral crystals in basalt are small and difficult to see. This image shows fresh basalt as it forms from cooling lava.

Sedimentary RockWeathering is the breakdown of rock by agents such as wind and water. Erosion is the transporting of the broken rock material, or sediments, to a new location, where it is deposited. Sediments may also contain plant and animal matter.As more sediment is deposited, it stacks up in layers. Eventually, the upper layers put pressure on the lower layers. This causes sediments to pack closer together in a process called compaction.Through the process of cementation, minerals from groundwater form between sediment grains, connecting the grains together to form rock.The rocks formed from deposition, compaction, and cementation of sediment are sedimentary rocks.

Sedimentary rocks often occur in distinct layers and sometimes contain fossils. Sedimentary rocks that are well-cemented hold together well, while poorly cemented rocks tend to crumble more easily. Some common sedimentary rock types include sandstone, siltstone, and shale. Sedimentary rocks that form mainly from chemical processes include limestone and dolomite. Evaporites, such as rock salt, are sedimentary rocks that form when minerals are left behind by evaporating water.

Sedimentary rocks commonly form in layers. These rock layers in the Grand Canyon represent a variety of sedimentary rock types,

including sandstone, siltstone, shale, limestone, and dolomite.

Metamorphic RockMetamorphosis means "transformation" or "change." The third major classification of rock is appropriately named metamorphic rock.Tectonic forces can push all types of rocks deeper into the Earth. These rocks are then subjected to extreme heat and pressure. If the rocks do not become hot enough to melt, these conditions can cause the crystal structure and texture of the rocks to change, forming a new kind of rock. Metamorphic rocks are rocks that form from other rocks under extreme heat and pressure.Some rocks have certain mineral grains that become flattened and line up in parallel planes or that separate into light and dark compositional bands when exposed to heat and pressure. These scenarios result in foliated metamorphic rocks, such as slate, phyllite, schist, and gneiss. Metamorphic rocks without these planes or bands are nonfoliated. Marble is a nonfoliated metamorphic rock that forms from the sedimentary rock limestone. Quartzite is a metamorphic rock that forms from quartz sandstone.

Phyllite is an example of a foliated metamorphic rock. Phyllite forms under moderate temperature and pressure conditions relative to other

types of metamorphic rocks.

SoilSoil is made up of weathered rock, minerals, and decaying plants and animals. It also contains air, water, animal wastes, and small living organisms. The conditions of the soil and the type of soil can impact what plants grow best there.

Soil is made of weathered rock and decaying plants and animals that have broken down into very small pieces. Soil is the top layer that covers the Earth. Soil also contains living organisms, such as worms and microorganisms. Microorganisms are too small to see with the naked eye.

Soil is Made up Partly of Weathered RocksWeathering breaks rocks down into smaller pieces. Over thousands of years, the rock pieces get smaller and smaller until they become particles of soil. Because most rocks are composed of minerals, these minerals also become part of the soil. Rock weathering is caused by wind, water, and ice. Moving water weathers off the rough edges of big rocks and makes the rocks smooth.The rock portion of the soil is made up of different-sized particles: sand, silt, and clay. These components give the soil different characteristics, such as texture.

Sand particles are larger than particles of silt or clay. Sand has a gritty texture, and water runs through it quickly.

Silt feels like powder because the grain size is small. The particles are smaller than sand, but larger than clay. Loess is a form of wind blown silt.

Clay has the smallest grains of any soil component. This small particle size makes clay have a sticky texture when it is wet. When clay dries, though, it makes hard clumps. Clay holds water the best of any soil component.

Soil Contains Decaying Plants, Animals & WastesSoil also comes from the decayed matter of plants and animals after they have died. Leaves that fall from trees and animal wastes also break down into soil. Decaying parts of plants and animals are called organic material. Organic material breaks down into a rich, dark substance called humus. Humus in the soil is important for helping new plants grow. It has a rich, almost sweet odor. Humus is most common in clay soil because it sticks to the clay particles.

In the picture of the tree stump, the wood is decaying into soil. Parts of the wood are still in large chunks. Over time they break into smaller and smaller pieces.

Soil Contains Living OrganismsSoil contains living organisms, such as earthworms, insects, fungi, and bacteria. Many of these organisms are too small to see with the naked eye. The mushroom shown below is a kind of fungus that is large enough to see without a microscope.

Soil Conditions and Plant GrowthDifferent types of soil are able to support different kinds of plant life. Soil comes in many different varieties and can have many different properties. Some important soil characteristics include: color composition pH level texture structure chemical composition permeability porosity

Soils vary in color. Some soils are black, others are red, and others are gray.

Soils come in many different varieties, including different colors.

The type of soil and the type of plants and animals that can live in the soil are determined by the composition of the soil, or how much of each material is present in the soil.A soil's pH level often determines which plants can survive in it and which plants cannot. A soil's pH level is an indication of how acidic it is. Most plants are able to

survive in soils within a certain pH range. Soils that are too acidic tend to dissolve nutrients too quickly for certain plants. Soils that aren't acidic enough tend to not dissolve enough nutrients for certain plants.Soils also vary quite a bit in terms of texture and particle size. Most soils are made up of particles of many different sizes and shapes. Some pieces of soil are very large and solid, while other pieces of soil may be very small and soft. Different plants thrive in soils of different textures.Soils can have many different structures. Some types of soil clump together in large segments. Other types of soil, such as sand, might not form such structures at all. Some plants require large solid structures for their growth and survival, while other plants are able to thrive under other conditions.Different soils have different chemical compositions. Plants depend on chemical interactions between the roots and the nearby soil. Plants tend to be adapted to soils of particular chemical compositions for this reason.Depending on many of these factors, different types of soil allow water to pass them at different rates. Soils that allow water to pass through them quickly are said to be permeable. Loosely packed soils with many solid particles, such as sand, tend to be quite permeable. Soils that are tightly packed with hard clay can often be less permeable.A soil's porosity is a measure of how much empty space is in it compared to its overall volume. Soils are not perfect solids; between individual particles are many empty spaces. These spaces can be very small, or they can be quite large. Soils that are more porous can absorb more water than soils that are less porous.Many plants do not grow well in sandy soil because of its loose texture and high porosity. It does not hold enough water or organic material to give most plants what they need. Clay soil is not ideal for many plants either. In clay, the particles are closely packed together, so roots cannot easily push through to grow. Clay soil has low porosity and low permeability.Plants grow best in a type of soil called loam. Loam is soil that contains a mixture of sand, silt, and clay. Loams have the best characteristics of each of the soil components. They have a somewhat loose, gritty texture from the sand, yet because of the silt and clay, they have a more balanced porosity and permeability. Loam can hold enough water to keep roots moist. Because of the moisture, if you try to squeeze loam into a ball, it will stick together, as shown in the picture below. But the ball will not hold together as tightly as a ball of clay soil would.

Human Environmental Impact & Stewardship

Human activities have significant effects on the environment. These effects can be either positive or negative.

Humans make use of the lands and waters of planet Earth in many different ways. Land is used for producing food, building shelters, disposing of wastes, and extracting raw materials. Water is used for fishing, energy production, waste disposal, and direct consumption. Through these activities, humans can impact their own quality of life as well as the health of wildlife and the environment. Some important human activities and their impacts are discussed below.

AgricultureHumans often use large sections of land for farming and raising domesticated animals. This can change the environment in many different ways.

Depending on the methods used, farming can change the type and quality of the land. For example, slash and burn farming is a type of farming that consists of cutting down and burning forests to make enough room to grow crops. This ruins the area for future farming because the fertile topsoil that had been protected by the forest is quickly washed away. Slash and burn also removes the oxygen-producing trees from the area, and creates harmful gases from the large fires needed to burn the area.

Even advanced farming techniques can deprive the soil of nutrients and make it difficult for anything to grow. However, some farming practices, such as crop rotation, can help reduce nutrient loss. Changing crops every two or three years can help replenish the nutrients and keep soil fertile because different plants use different amounts of nutrients and attract different pests. In general, healthy soil can be used to grow healthy crops, and soil must be monitored to ensure that it remains healthy in terms of the amount of nutrients, pollutants, and organisms it contains.Raising domesticated animals such as cows, can harm the environment if ranchers allow the animals to overgraze. Overgrazing removes too much vegetation from an area of land, which increases erosion and reduces soil fertility. Erosion can also strip soil of nutrients vital for plant life. If such practices go unchecked, desertification can be the result. When desertification happens, land that was once fertile can no longer support much plant life and cannot be used as farmland anymore.One method of reducing erosion that can be used in an agricultural setting is contour plowing. In this technique, crops are planted in horizontally plowed rows on hills instead of in rows that run up and down the hill. This slows down runoff water as it travels down the hill and therefore reduces the amount of soil the runoff carries with it.Farming practices can also pollute water resources. Chemical pesticides can leach into water and cause neurological disorders, cancer, and reproductive problems for organisms drinking or swimming in the water. Organic and inorganic fertilizers used by farmers to increase crop production can produce nitrogen and phosphorous runoff. When these nutrients reach bodies of water such as streams, lakes, or an ocean—even hundreds of miles away—they can lower oxygen levels and kill many types of organisms, including fish. Runoff that contains wastes from livestock production facilities can also lead to contamination of ground or surface water with bacteria and other organisms that cause disease.

FishingHumans fish to get food or for recreation. If done responsibly, fishing can cause minimal harm to an environment. Sometimes, though, humans do not fish responsibly and can cause irreparable damage to ecosystems.

Fishing can cause major disruptions to aquatic ecosystems or even destroy whole populations of fish.

For example, drift nets are huge nets that can be several kilometers long and catch many more fish than do smaller, more traditional nets. Widespread use of these nets around the world can greatly reduce fish populations. Also, many other marine animals, such as dolphins, turtles, seabirds, and whales, are commonly caught and killed by drift nets. To help prevent these scenarios, the United Nations and national governments have enacted resolutions and regulations limiting the size and use of drift nets.Overfishing is another issue that can occur. This happens when humans catch too many of a specific type of fish. This disrupts the balance of the ecosystem and can lead to extinction. 

Waste DisposalHuman activities tend to produce wastes. Sometimes these wastes can be reused or recycled; other times they are deposited into the land, air, or water.

Most of the solid waste that humans produce ends up in landfills. Landfills are simply sites where solid waste materials are stored. In addition to simply contaminating the area of land it occupies, landfills tend to contaminate the water that comes into contact with it.Water that is contaminated from the various organic and inorganic substances with which it comes into contact as it migrates through the waste is known as leachate. Water moving through a landfill inevitably becomes contaminated as leachate, which is undrinkable and often toxic. Most modern landfills in the U.S. have leachate collection and monitoring systems. These systems generally involve a layer of durable plastic that is placed beneath the waste to prevent water from seeping into the surrounding soil. But many such systems eventually fail, allowing nearby water sources to become contaminated over time. If the leachate, or other pollutant, contaminates soil used for growing crops, the pollutants in the soil can be taken up into the plants and passed on to the humans who eat the plants.Waste products from human activities are also sometimes released directly into the water, either unintentionally or due to lack of regulation by environmental agencies. Any water containing human or animal waste or waste from industrial processes often makes its way into bodies of water that are collection points for their

watersheds. If the waste water contains foreign substances or is a different temperature than the natural body of water, then natural ecosystems can be impacted. In addition, people drinking from the water can become ill if there are dangerous levels of harmful substances in it. Governments and environmental regulation agencies try to keep drinking water sources clean and safe by preventing people and industries from putting pollutants into it. They also monitor the water to ensure that amounts of pollutants are below toxic levels.Human activities also produce wastes that are released directly into the air. Some air pollutants return to Earth in the form of acid rain and snow, which corrode statues and buildings, damage crops and forests, and make lakes and streams unsuitable for fish and other plant and animal life.

Energy ProductionMost of the electrical energy produced by humans is generated by burning fossil fuels such as coal, oil, and natural gas. Humans also burn oil products to generate energy for transportation. Each of these ways of generating energy produces pollution that is released into the air. The U.S. Environmental Protection Agency recognizes a number of substances that are released during energy production as pollutants: ozone carbon Monoxide carbon Dioxide nitrogen Oxides sulfur Dioxide lead mercury particulate Matter

Humans also generate electrical energy by building dams and harnessing the energy of moving water as it falls over the dams. After a dam is constructed, producing electricity in this manner does not release pollutants into the air; it does, however, change the natural flow of water. Changing the way that water naturally flows can damage some ecosystems and ruin others.

Obtaining Raw MaterialsHumans use thousands of raw materials such as water, wood, coal, oil, iron ore, uranium, and stone. These materials are used for making consumer products, constructing buildings, generating electricity, and direct consumption. Obtaining these materials can often do damage to the environment and natural ecosystems. Logging, for instance, can change or destroy plant and animal habitats.

Mining is another method by which humans obtain raw materials. Mining can permanently alter landscapes and pollute nearby bodies of water.Perhaps the most important raw material for human life is water. Humans obtain water in many different ways including diverting it from natural rivers or lakes by building dams, aqueducts, and reservoirs. Such practices can change the natural flow of water, alter or destroy ecosystems, and even impact the lives of people living downstream.

Construction & UrbanizationHuman populations have drastically increased in size over the past 150 years and have become increasingly concentrated in urban areas. As the human population grows, the need for more cities and towns increases. The construction of the cities and towns leads to an increase in pollution and negative impacts on habitats. For example, there are many types of impervious covers associated with towns and cities. These are types of surfaces that water cannot penetrate, so the water runs off of it very fast. The fast-moving water, as is strikes the soil surrounding the impervious area, can pick up and carry more soil particles than slow-moving water. Therefore, impervious surfaces—such as roads, parking lots, and rooftops—can cause increased erosion and even the formation of deep gullies.

People who live in urban regions tend to consume more resources than people who live in rural regions. These resources include electric energy from the burning of fossil fuels and some types of food, such as meat products. The environmental impacts from this include increased air pollution from coal-fired power plants and the ecological effects of raising additional livestock to support a population that eats more meat.Urbanization can also impact local weather patterns. Urban areas tend to be warmer than the rural areas that surround them. This is mainly a result of the way in which the materials humans use for building, such as concrete, absorb and radiate energy from the Sun. When a city has higher temperatures than surrounding areas, it is known as the "heat island" effect. Low pressure systems can form over cities as hot air rises, cools, and is replaced by moist air. This can make clouds and fog more likely to form over cities, which can contribute to smog and other air quality issues.

Conservation & StewardshipConservation and stewardship are the careful use and preservation of Earth's natural resources. These practices are based on the idea that people should plan ahead to minimize negative impacts of human activity. If people consider what impact their choices have on ecosystems first, they can look for ways to minimize that impact. For example, when people practice soil conservation, they study, plan, or implement ways to protect the quality of the soil and prevent loss of soil through erosion. Technology, such as remote sensing tools, can be used for monitoring as a part of conservation and stewardship efforts. Other types of technology that have been used in resource conservation include: GPS can be used to mark diseased trees for removal or to track locations of endangered

species

helicopters and airplanes can be used to fight forest fires and reseed burned land

silt fences and other types of runoff barriers can be used to reduce soil erosion

new forestry equipment can help reduce the environmental impact of logging and forest management

Although there are no easy solutions to the many negative environmental impacts that human activities can have, there are, in fact, many human activities that can have a positive impact on the environment. Some of these activities can be summarized simply as reducing, reusing, recycling, and renewing.Reducing is the act of consuming fewer natural resources and decreasing the amount of waste a person creates. Reducing can come in many forms. Automobile manufacturers, for example, can reduce the amount of materials they consume by simply manufacturing smaller cars. Consumers can reduce the amount of fossil fuel energy they consume by operating smaller cars. Energy-efficient appliances and home heating systems also reduce the amount of resources needed to operate them.Reusing can be giving something a different purpose, such as using an old glass jar to store extra nails and screws. It can also be the act of passing something along once you are done with it. For instance, giving clothes you've outgrown to charity or to your younger brother or sister is reusing. It keeps the clothes out of the landfill, and it also cuts down on the amount of new waste created in the production and purchase of new clothes.Recycling is the process of making new products from products that have been used before. Since fewer new resources are needed to make the recycled products, resources are conserved. For instance, recycling paper helps conserve trees. Recycling aluminum cans helps to conserve aluminum.

Renewing is the process of working to help increase supplies of a resource. Planting trees is one way to help renew a resource and therefore practice environmental stewardship. Helping protect and restore populations of endangered species or species that have been overfished or overhunted is another type of renewal.