Earth+Science

=The Earth System= The Grand Canyon is made up of different parts. Rock forms the canyon walls. Water flows through the canyon in the form of a river, which carves away the rock. Animals such as deer drink the river's water. And air fills the canyon, allowing the animals to breath. All these parts work together. So the environment of the Grand Canyon can be though of as a system. A system is a group of parts that work together as a whole. The Earth system involves a constant flow of matter though different parts. For example, you may know that in the water cycle, water evaporates from the ocean, rises into the atmosphere, and then falls from the ksy again as rain. The rainwater then flows into and over the Earth, and then back to the ocean.

You might be surprised to learn that rock, too, cycles through the Earth system. For example, new rock can form from molten material inside the Earth called magma. This material can rise to the surface and harden on land to form new rock. The new rock can then erode into small pieces. The pieces can be washed into the ocean, where they then may sink to the bottom as small particles, or sediment. If enough of the small particles collect, the weight of the sediment can crush all the particles together. The particles can then be cemented together to form new rock. The flow of rock through the Earth System is called the rock cycle.

The constant flow, or cycling, of matter thought the Earth System is driven by energy. Energy is the ability to do work. The energy that drives the Earth system has two main sources: heat from the sun and heat flowing out of Earth as it cools.

=Looking at the Earth= toc Geography is the study of the earth and its people. Maps and globes are some of the tools used to study the physical and human characteristics of our planet. There are many tools available today to help geographers provide information used by government and business leaders as they plan and make decisions. Our planet, Earth, is part of a solar system made up of a sun, nine planets, and thousands of smaller bodies. Life on Earth could not exist without the heat and light provided by the sun or the atmosphere of gases that surrounds the planet. The earth's rotation creates a twenty-four hour day and night, while its orbit around the sun and 23 ½ degree tilt produce the seasons.

Inside the earth are layers of varying thickness and composition: the inner core, outer core, mantle, and crust. Scientists theorize that volcanoes, earthquakes, and continental drift are caused by the movement of tectonic plates that float on top of the liquid rock in the mantle. The forces of weathering and erosion also continually change the earth's surface.

People have adapted in order to live on various landforms. Mountains, plateaus, valleys, and other landforms are found on land and under the oceans. About 70 percent of the earth's surface is water. =Landforms= Earthquakes and volcanic eruptions are two forces that shape the Earth. They provide clues about the Earth's structure and are one reason why the Earth's surface constantly changes. To understand events like volcanic eruptions and earthquakes, geographers study the Earth's structure. Pictures of the earth show a great deal of water and some land.The water covers about 75% of the earth's surface. In part, continents are unique because of their landforms, or shapes and types of land. Mountains are landforms that rise usually more than 2,000 feet above sea level. They are wide at the bottom and rise steeply to a narrow peak or ridge. Hills are lower and less steep than mountains. A plateau is a large, elevated piece of flat land. Plains are large areas of flat or gently rolling land. Many are along coasts, while others are in the interior.

Forces like volcanoes slowly build up the earth's surface; other forces slowly break it down. Often, the forces that bread the earth down are not as dramatic as volcanoes but the results can last just as long. Weathering is a process that breaks down rock into tiny pieces. Three things cause weathering: wind, rain and ice. Slowly but surely, they wear away the earth's landforms. Hills and low, rounded mountains show what weathering can do. Wind and rain have weathered the Appalachian Mountains in the eastern United States into much lower peaks than they once were. Weathering also helps to create soil. Tiny pieces of rock combine with decayed animal and plant material to form soil.

Once this breaking down has taken place, small pieces of rock may be carried to new places by a process called erosion. Weathering and erosion slowly create new land forms.

**The Earth's Layers** If scientists have never studied any materials from a depth below 7 miles, then how is it that we know what is in the center of the Earth? How can we know what the core of the Earth is made of, if we have never seen it? The answer is actually quite simple. While it is true that we can not study the Earth’s core using visible light, we can study it using other senses. The most important thing we use to sense the Earth’s core are seismic waves. Seismic waves are waves of energy caused either by earthquakes, or by massive man-made explosions. Scientists are able to measure these waves as they pass through the Earth. As these waves encounter different materials, they change in important ways, becoming longer, shorter, faster, or slower. Geologists study these changes in the waves, and are able to draw conclusions about what the core of the Earth must look like.

Geologists also can learn a lot about the core of our planet by looking at Earth’s magnetic field. The Magnetic field is created by massive circulations of hot liquid mantel beneath the Earth’s surface. These clues lead geologists to believe that the Earth is made of four distinct layers. These layers are the crust, the mantel, the outer core, and the inner core.


 * Crust** The first layer consists of about 10 miles of rock and loose materials, scientists call the crust. Underneath the continents, the crust is almost three times as thick, as it is under the oceans. There are 90 known elements that exist in the Earth’s crust. These elements combine with one another in a number of natural ways, creating molecules known as minerals. There are around 3,700 known minerals found in the Earth’s crust, we dozens of new minerals being discovered each and ever year. At the surface of the Earth we generally do not find very much solid rock. The solid rock is covered by several feet of ground up, weathered rock, known as regolith, or dirt. However, in some cases, this solid rock does protrude out of the ground, in what is known as an outcropping. In order to better understand the some 3,700 different types of known rocks, scientists group them into three groups, based on how they are similar, and how they are igneous rock, sedimentary rock, and metamorphic rock.


 * Mantle** Traveling beyond the Earth’s crust, we next encounter the mantle. The mantle extends to a depth of approximately 1,800 miles, and is made of a thick solid rocky substance that represents about 85% of the total weight and mass of the Earth.The first 50 miles of the mantle are believed to consist of very hard rigid rock. The next 150 miles or so is believed to be super-heated solid rock, that due to the heat energy is very weak. Below that for the next several hundred miles, the Earth mantle is believed to once again be made up of very solid and sturdy rock materials.


 * Outer Core** Traveling still deeper within the Earth, we next would encounter the Earth’s outer core, which extends to a depth of around 3000 miles beneath the surface. It is believed that this outer core is made up of super-heated liquid molten lava. This lava is believed to be mostly iron, and nickel.


 * Inner Core** Finally, we would reach the Earth’s inner core. The inner core extends another 900 miles inward towards the center of the Earth. It is believed that this inner core is a solid ball of mostly iron, and nickel.

= =

**Constructive and Destructive Forces**

You may not realize it, but the land is changing all the time. The Earth is always working to build new land and to wear down the old.

Sometimes changes to the Earth happen rapidly, but other changes can take millions of years!

EROSION
Wind, water, and ice are the three agents of erosion, or the carrying away of rock, sediment, and soil. Erosion is distinguished from weathering — the physical or chemical breakdown of the minerals in rock. However, weathering and erosion can happen simultaneously. Erosion is a natural process, though it is often increased by humans’ use of the land. Deforestation, overgrazing, construction, and road building often expose soil and sediments and lead to increased erosion. Excessive erosion leads to loss of soil, ecosystem damage, and a buildup of sediments in water sources. Building terraces and planting trees can help reduce erosion.

GLACIERS
In the Arctic and sub-Arctic, glacial erosion has shaped much of the landscape. Glaciers primarily erode through plucking and abrasion. Plucking occurs as a glacier flows over bedrock, softening and lifting blocks of rock that are brought into the ice. The intense pressure at the base of the glacier causes some of the ice to melt, forming a thin layer of subglacial water. This water flows into cracks in the bedrock. As the water refreezes, the ice acts as a lever loosening the rock by lifting it. The fractured rock is thus incorporated into the glacier’s load and is carried along as the glacier slowly moves.

Abrasion happens when the glacier’s ice and rock fragments act as sandpaper, crushing the rock into finely grained rock flour and smoothing the rock below. Meltwater streams of many glaciers are grayish in color due to high amounts of rock flour.

VOLCANOES
A volcano is simply an area where magma, or molten rock, from the earth’s mantle reaches the earth’s surface, becoming lava. Most volcanoes occur at plate boundaries, where two plates are moving away (diverging) or together (converging). A few volcanoes like the Hawaiian Islands form from a hot spot, or a weak spot in earth’s crust, where magma forces its way to the surface.

Volcanic eruptions may be explosive (violent) or effusive (passive), depending on the lava chemistry (amounts of silica and dissolved gases). Silica is a mineral found in nature as sand or quartz. High levels of silica mean very viscous (thick) lava, and low levels mean more fluid lava. Dissolved gases build up inside the volcano, much like a can of soda or other carbonated beverage. The higher the level of gas, the more pressure that builds – and the more violent an explosion. The combination of silica and dissolved gas levels determines the type of eruption and shape of the volcano. Volcanoes are classified into four types, based on their lava chemistry and shape.

EARTHQUAKES
Seismic activity (earthquakes) is most often associated with tectonic plate boundaries. As plates slowly move, their jagged edges stick and suddenly slip, causing an earthquake.

The Gakkel Ridge underneath the Arctic Ocean experiences small earthquakes that accompany the volcanic activity found in the area. Antarctica, which lies in the center of a tectonic plate, does not experience many earthquakes. However, seismic activity is associated with eruptions of Mt. Erebus.

**The Plate Tectonic Theory** Scientists now believe that about 250 million years ago, a super-continent known as Pangaea existed. This super-continent was made up of all the continents on Earth. Over time, these continents have broken apart, and slowly drifted away from one another. This drift continues today, so that the form the Earth takes today is not by any means the final shape of our Earth.


 * Continental drift** was a theory proposed in 1912 by Alfred Wegener which postulated the movement of continents . This theory is a part of the concept of plate tectonics . Continents have been drifting for hundreds of millions of years . [|Pangea animation]


 * Cause of Continental Drift** Through convection, heat flows from the Earth 's core to its crust. As the asthenosphere is plastic , the lithosphere floats along the convection currents. Initially ridiculed in North America the idea was widely accepted in Europe by the 1950s . In the 1960s geological research led to acceptance in North America. The similarity of Southern continent fossil faunas and some geological formations led the relatively small number of Southern hemisphere geologists to conjecture as early as 1900 that all the continents had once been joined into a supercontinent.


 * Various Data** South America and Africa are moving apart at 3cm per year, due to the Mid-Atlantic Ridge.

There exist two main forms of more geological evidence evident: rock sequences and magnetic stripes. When the rock strata of the tips of separate continents are very similar it suggests that these rocks were formed in the same way implying that they were joined initially. For instance, some parts of Scotland contain rocks very similar to those found in eastern North America. The second piece of evidence arises when the rocks were formed from magma erupting out of a volcano. When this happens the iron particles align with the earth's magnetic field and set in this position. As the earth's magnetic field flips every half-million years, strips of land of alternating magnetic orientation are formed - symmetrical from the volcano. This showed how some plates are moving away from each other.
 * Evidence for continental drift** Nowadays there exists lots of evidence for continental drift. The most obvious is the way in which the continents seem to fit jigsaw-like (for example Africa and South America) together when looked at on a map. More scientific evidence comes in the form of plant and animal fossils of the same age found around different continent shores, suggesting that they were once joined. For example the fossils of the freshwater crocodile found in Brazil and South Africa. Another illustrative example is the discovery of fossils of the aquatic reptile // Lystrosaurus // from rocks of the same age from locations in South America, Africa , and Antarctica . There is also living evidence - the same animals being found on two continents. An example of this is a particular earthworm found in South America and South Africa.

Major Types of Plate Movement
Scientists now have a fairly good understanding of how the plates move and how such movements relate to earthquake activity. Most movement occurs along narrow zones between plates where the results of plate-tectonic forces are most evident. There are four types of plate boundaries:
 * **Divergent boundaries** -- where new crust is generated as the plates pull away from each other. Divergent boundaries occur along spreading centers where plates are moving apart and new crust is created by magma pushing up from the mantle. Picture two giant conveyor belts, facing each other but slowly moving in opposite directions as they transport newly formed oceanic crust away from the ridge crest. Perhaps the best known of the divergent boundaries is the Mid-Atlantic Ridge. This submerged mountain range, which extends from the Arctic Ocean to beyond the southern tip of Africa, is but one segment of the global mid-ocean ridge system that encircles the Earth. The rate of spreading along the Mid-Atlantic Ridge averages about 2.5 centimeters per year (cm/yr), or 25 km in a million years. This rate may seem slow by human standards, but because this process has been going on for millions of years, it has resulted in plate movement of thousands of kilometers. Seafloor spreading over the past 100 to 200 million years has caused the Atlantic Ocean to grow from a tiny inlet of water between the continents of Europe, Africa, and the Americas into the vast ocean that exists today.
 * **Convergent boundaries** -- where crust is destroyed as one plate dives under another.The size of the Earth has not changed significantly during the past 600 million years, and very likely not since shortly after its formation 4.6 billion years ago. The Earth's unchanging size implies that the crust must be destroyed at about the same rate as it is being created, as Harry Hess surmised. Such destruction (recycling) of crust takes place along convergent boundaries where plates are moving toward each other, and sometimes one plate sinks (is //subducted//) under another. The location where sinking of a plate occurs is called a //subduction zone.// The type of convergence -- called by some a very slow "collision" -- that takes place between plates depends on the kind of lithosphere involved. Convergence can occur between an oceanic and a largely continental plate, or between two largely oceanic plates, or between two largely continental plates.
 * **Transform boundaries** -- where crust is neither produced nor destroyed as the plates slide horizontally past each other.The zone between two plates sliding horizontally past one another is called a //transform-fault boundary,// or simply a //transform boundary.// The concept of transform faults originated with Canadian geophysicist J. Tuzo Wilson, who proposed that these large faults or //fracture zones// connect two spreading centers (divergent plate boundaries) or, less commonly, trenches (convergent plate boundaries). Most transform faults are found on the ocean floor. They commonly offset the active spreading ridges, producing zig-zag plate margins, and are generally defined by shallow earthquakes. However, a few occur on land, for example the San Andreas fault zone in California. This transform fault connects the East Pacific Rise, a divergent boundary to the south, with the South Gorda -- Juan de Fuca -- Explorer Ridge, another divergent boundary to the north.
 * **Plate boundary zones** -- broad belts in which boundaries are not well defined and the effects of plate interaction are unclear.Not all plate boundaries are as simple as the main types discussed above. In some regions, the boundaries are not well defined because the plate-movement deformation occurring there extends over a broad belt (called a //plate-boundary zone//). One of these zones marks the Mediterranean-Alpine region between the Eurasian and African Plates, within which several smaller fragments of plates //(microplates)// have been recognized. Because plate-boundary zones involve at least two large plates and one or more microplates caught up between them, they tend to have complicated geological structures and earthquake patterns.

We can measure how fast tectonic plates are moving today, but how do scientists know what the rates of plate movement have been over geologic time? The oceans hold one of the key pieces to the puzzle. Because the ocean-floor magnetic striping records the flip-flops in the Earth's magnetic field, scientists, knowing the approximate duration of the reversal, can calculate the average rate of plate movement during a given time span.

Evidence of past rates of plate movement also can be obtained from geologic mapping studies. If a rock formation of known age -- with distinctive composition, structure, or fossils -- mapped on one side of a plate boundary can be matched with the same formation on the other side of the boundary, then measuring the distance that the formation has been offset can give an estimate of the average rate of plate motion. This simple but effective technique has been used to determine the rates of plate motion at divergent boundaries, for example the Mid-Atlantic Ridge, and transform boundaries, such as the San Andreas Fault. To date the GPS has been the most useful for studying the Earth's crustal movements. Twenty-one satellites are currently in orbit 20,000 km above the Earth as part of the NavStar system of the U.S. Department of Defense. These satellites continuously transmit radio signals back to Earth. To determine its precise position on Earth (longitude, latitude, elevation), each GPS ground site must simultaneously receive signals from at least four satellites, recording the exact time and location of each satellite when its signal was received. By repeatedly measuring distances between specific points, geologists can determine if there has been active movement along faults or between plates. The separations between GPS sites are already being measured regularly around the Pacific basin. By monitoring the interaction between the Pacific Plate and the surrounding, largely continental plates, scientists hope to learn more about the events building up to earthquakes and volcanic eruptions in the circum-Pacific Ring of Fire. Space-geodetic data have already confirmed that the rates and direction of plate movement, averaged over several years, compare well with rates and direction of plate movement averaged over millions of years.


 * W **hat is topography?

Topography describes the physical features of an area of land. These features typically include natural formations such as mountains, rivers, lakes, and valleys. Manmade features such as roads, dams, and cities may also be included. Topography often records the various elevations of an area using a topographical map.

Topographical Features

Topography studies the elevation and location of landforms. Topographical Map
 * Landforms - Landforms studied in topography can include anything that physically impacts the area. Examples include mountains, hills, valleys, lakes, oceans, rivers, cities, dams, and roads.
 * Elevation - The elevation, or height, of mountains and other objects is recorded as part of topography. It is usually recorded in reference to sea level (the surface of the ocean).
 * Latitude - Latitude gives the north/south position of a location in reference from the equator. The equator is a horizontal line drawn around the middle of the Earth that is the same distance from the North Pole and the South Pole. The equator has a latitude of 0 degrees.
 * Longitude - Longitude gives the east/west position of a location. Longitude is generally measured in degrees from the Prime Meridian.

A topographical map is one that shows the physical features of the land. Besides just showing landforms such as mountains and rivers, the map also shows the elevation changes of the land. Elevation is shown using contour lines.

When a contour line is drawn on a map it represents a given elevation. Every point on the map touching the line should be the same elevation. On some maps, numbers on the lines will let you know what the elevation is for that line.

Contour lines next to each other will represent different elevations. The closer the contour lines are to each other, the steeper the slope of the land.

The lower map shows the contour lines for the above hills

Ways Topography is Studied

There are a number of ways that information is gathered to make topographical maps. They can be divided into two primary methods: direct survey and indirect survey.

Direct survey - A direct survey is when a person on the ground uses surveying equipment, such as levels and clinometers, to directly measure the location and elevation of the land. You have probably seen a surveyor along the road sometime making measurements by looking through a leveling instrument sitting on a tall tripod.

Indirect survey - Remote areas may be mapped using indirect methods. These methods include satellite pictures, images taken from planes, radar, and sonar (underwater).

Worker performing a survey

What is topography used for?

Topography has a number of uses including: = =
 * Agriculture - Topography is often used in agriculture to determine how soil can be conserved and how water will flow over the land.
 * Environment - Data from topography can help to conserve the environment. By understanding the contour of the land, scientists can determine how water and wind may cause erosion. They can help to establish conservation areas such as watersheds and wind blocks.
 * Weather - The topography of the land can have an impact on weather patterns. Meteorologists use information on mountains, valleys, oceans, and lakes to help predict the weather.
 * Military - Topography is also important to the military. Armies throughout history have used information on elevation, hills, water, and other landforms when planning their military strategy.