Advanced World Geography Chapter 1 Exploring Geography

Transcription

1 Advanced World Geography Chapter 1 Exploring Geography Lesson 2 A Changing Earth In this lesson you will learn how to: describe how the earth is a changing planet that is affected by geologic processes. describe the forces within the earth and how they create and change landforms on the surface. describe the theory of plate tectonics and how it suggest multiple answers regarding the earth s landforms. Changes Within the Earth One of the chief tasks geographers take on is to understand the earth s continuous changes. Earth is not a stagnant, quiet planet. Earthquakes knock over buildings and create huge cracks in the ground. Volcanoes erupt with scorching lava and hazardous gasses. These changes are dramatic and spectacular, but they are not the only ways in which the earth changes. There are many different processes, some striking and others subtle, that are always hard at work shaping the earth we inhabit. Structure of the Earth Geology is the study of the earth s physical structure and history. It looks to the ancient history of the earth for answers. Geologists try to figure out what changes occurred in the earth s past and why these changes occurred. From their findings, they try to predict any future changes that could occur. David Wunsch and the New Hampshire state geologist, examining an area where the Suncook River once flowed. Source:NewYorkTimes

2 Inside the Earth. Scientists have come up with a pretty good idea of what the center of the earth is like. Its center is known as the core. It consist of extremely hot metal, which is mainly iron mixed with some nickel. It is divided into two layers, the inner core and the outer core. The inner core is believed to be dense and solid. It is about 780 miles thick. The outer core is so hot that its metals are molten, or liquid. It is about 1,370 miles thick. Because of the earth s rotation, the outer core spins around the inner core, causing the earth's magnetism. Surrounding the core is the mantle. The mantle is a thick layer of rock. Scientists think the mantle is 1,800 miles thick and makes up nearly 80 percent of the earth's total volume. The rock in the mantle is mostly solid, with some of the upper layers possibly being pliable. The mantle also holds pockets of magma, which is melted rock. Source: uvm.edu The crust, or the rocky surface layer, is astonishingly thin, like the icing on a cake. The oceanic crust, only 5-7 miles thick, is the thinner part of the crust, which is located below the oceans. The oceanic crust consists of mainly basalt without olivine, or tholeiitic basalt. Basalt is dark, fine and gritty, with a volcanic structure. It is fashioned out of molten lava, which cools off quickly. The grains are so tiny that they are only detectable under a microscope. Unlike the oceanic crust, the continental crust is thick, averaging 22 miles, and is extremely uneven. The continental crust is older than the oceanic crust, some rocks being 3.8 billion years old. It is primarily made up of igneous rocks and is divided into two layers. The upper layer primarily consists of granite rocks, while the lower layer consists of basalt and diorite. Granite is lightly-colored, course and grainy, magma. Diorite has the same composition, but it's scarcer than granite, and is probably formed by impurities in the granite-magma. Natural forces often interact with and affect the crust, sometimes creating landforms or natural features found on the earth s surface.

3 Land, Air, and Water. Often, geographers speak of the various elements of the natural environment of the earth as a set of related spheres which are dominated by various physical forms. Landforms, soil, rocks, and other features of the surface make up the lithosphere. The layer of air, water, and other substance about the surface of the earth is called the atmosphere. The hydrosphere, however, is made up of water in oceans, lakes, rivers, and even water found under the ground. The world of plants, animals, and other living organisms that inhabit the land and waters of the earth make up the biosphere. Physical geography looks at the way in which these spheres function and interact with one another and with people. Pictures taken of the earth from space give a clear picture of the saying that the earth is truly a watery planet. Over 70 percent of the earth s surface is covered by water. Most of this water is salt water, which can be found in the oceans and seas. The huge landmasses seen in the oceans are the continents. Though some of these landmasses are not totally separated by ocean waters, geographers still classify them as seven separate continents. Of these continents, Asia is the largest and Australia is the smallest. Each continent contains various landforms. Antarctica, however, has its landforms hidden by ice. Often landforms are classified according to differences in relief, or the different in elevation between the lowest and highest points. Also important, is whether they rise little by little or suddenly. Source: Public Domains

4 The main kinds of landforms are mountains, hills, plateaus, and plains. Rising at least 2,000 feet about the terrain that surround it, mountains have high relief. Hills, however, are lower, rounded, and usually less steep than mountains. The elevation of the land around the landform determines whether it is a hill or a mountain. Also, what we may see as a mountain in western North America, may be seen as a hill in the British Isles. Everything depends on the relative height of nearby landmasses in the area. This picture shows the various land and water features that can be found on earth. A plateau is also an elevated area, but has a level surface. Many plateaus have deep gullets or canyons, which make the surface appear rough instead of flat. There is at least one side of the plateau that rises about the surrounding land steeply. Plains are also considered landforms. A plain is a flat or gently rolling areas that has very few changes in elevation. Many plains are located along coasts. Other landforms include valleys, canyons, and basins. There are also various geographical features of landscapes that consists of rivers, peninsulas, and islands.

5 Inner Forces The questions that is often asked by geographers or geologists when looking at an area of land is, What forces shaped the mountains, plains, and other land forms that are here? Internal forces that originate in the earths interior first shape landforms. Volcanism is one of these forces. It involves the movement of the magma inside the earth. The other main forces that occur internally are movements that fold, lift, bend, or break the rocks on the earth s crust. Volcanoes. The people of ancient Rome believed the god Vulcan worked beneath the earth with hot iron and gold at his forge. In honor of Vulcan, a fiery island off Italy s coast was named Vulcano, and all the mountains formed by molten rock were called volcanoes. Volcanoes form when molten rock, or magma, beneath the surface of the earth breaks through the earth s crust. On the surface, the lava might flow evenly, making a plateau-like shield volcano. Cinders and ash erupting form the break in the ground sometimes produces small cinder cones. Unique cone-shaped mountains are fashioned as sporadic sequences of explosive eruptions and smooth lava flows from the volcano. A prime example of this type of volcano is Mount Fuji, which is located in Japan. Changes in the Earth s Crust. The complex movements that bend and break the crust of the earth vary. A fold results from rock layers bending and buckling. Other stresses on rocks cause faults, or cracks in the earth's crust. Rocks on either side of a fault sometimes slip or suddenly move. On one side of a fault, rocks might move sideways, up or down in reaction to the rock on the other side of the fault. A rock on either side of a fault may slowly move and produce subtle, unnoticeable changes. A large, sudden movement along a fault, however, can send out shock waves through the earth and cause an earthquake. Nonetheless, whether rock layers fault or fold, it is determined by the solidity of the rock and the power of the movement. Mount Fiji located in Japan.

6 Geologic History The majority of the changes to the surface of the earth happen so slowly that they are not immediately noticeable to the human eye. Much of the earth s history has been reconstructed by geologists from the record they read in the rocks. For years and years, scientists believed that the essential arrangement of oceans and continents were secure and permanent. These days, the accepted idea by most is that the earth s landmasses have broke apart, rejoined, and moved to other parts of the earth. The plate tectonic theory, which suggest answers to many perplexing questions concerning the landforms on earth, is formed partially by this concept. Plate Tectonics. The theory of plate tectonics suggest that the earth's outer shell is not one solid piece of rock. The lithosphere, or the earth s crust and the brittle upper layer of the mantle, is broken into many different plates that move. These plates are different sizes and vary in thickness. The North American Plates reaches from the mid-atlantic Ocean to the northern tip of Japan. In contrast, the Cocos Plate covers a tiny area in the Pacific Ocean, west of Central America. The plates are not fastened in place, sliding over a hot, pliable layer of mantle. Source: worldbook.com The oceans and continents of earth move atop the plates as they move in differing directions. The map above shows the boundaries of the different plates and the direction they move. For instance, the Pacific Plate and the Nazca Plate are moving apart. However, the Nazca Plate and the South American Plate are moving toward one another. Most of the world earthquakes, volcanoes, and other geologic event happen along the boundaries where plates meet. The theory of plate tectonics has been widely accepted since the 1960 s. It was based on the early ideas and research, but it included two other theories, continental drift and the seafloor spreading.

7 Plate Tectonics YouTube

8 Continental Drift. People noticed that some of the continents fit together like pieces from a jigsaw puzzle as early as the 1600 s. Could it be possible they were once one big landmass? In the early 1900 s a German explorer and scientist, Alfred Wegner, came up with the continental drift theory. He proposed that there was once a supercontinent called Pangaea, from the Greek word pan, which means all. In his theory, he said that 180 million years ago Pangaea started breaking apart into separate landmasses. Wegener found evident that showed fossils form South American, Africa, India, and Australia that were almost identical to support his theory. Even the rocks were similar. Still, many scientists were left unconvinced by the evidence he presented. Seafloor Spreading. The theory of sea floor spreading also supports the theory of Continental Drift. This theory emerged from the study of the ocean floor. Scientists used sonar to map the floor of the Atlantic Ocean. The sonar showed scientists that the ocean was not flat, instead resembling the landforms of the continents. The landforms found included rocky mountains, deep canyons, and wide plains. Also, they found that the rocks on the ocean floor were much younger than those found on the continents. The rocks near the underwater ridge system, or a series of underwater mountains that extend around the world, were the youngest rocks of all. The first explanation for these younger rocks was the theory of the seafloor spreading, first suggested in the 1960 s. This theory states that molten rock from the mantle rises from beneath the underwater ridge and breaks through a split at the top of the ridge. This split is known as a rift valley. From there, the rock spreads out on both sides of the ridge. Older rocks are carried away as the seafloor moves away from the ridge. This theory, as well as the older continental drift theory, became part of the theory of plate tectonics. This picture is showing the continental drift theory and the supercontinent called Pangaea. The number in the lower right represents millions of years ago. Source: ucmp.berkeley.edu

9 Subduction zone, where two plates meet. Mountains are usually formed from this type of boundary. Source: fs.fed.us Plate Movement. In the 1920 s, one of the biggest reasons people had doubts about the continental drift theory was because there was no explanation of how the continents moved. What force would be strong enough to push enormous plates sliding around the world? Today, however, most scientists think the force is a process called convection. Convection is a circular movement caused when matter is heated. The matter then rises and expands, cools and falls. This is believed to be occurring in the mantle rock under the plates. Convection is believed to be driven by heat energy from the slow decay of matter beneath the crust of the earth. Meeting of Plates. The places were plates meet are some of the most restless parts of the earth. Plates have the ability to pull away from one another, crash into one another, or slide past one another. When plates pull away from each other a process known as spreading occurs. In this process, they form a diverging plate boundary or spreading zone. These kinds of areas most likely have a rift valley, earthquakes, and volcanic action. When plates crash into each other, the results depend on the types of plates involved. Continental plates float higher since their crust is lighter than oceanic crust. Because of this, when an oceanic plate meets a continental plate, it slides under the lighter plate and into the mantle. The oceanic rock then melts deep inside the earth. This process is known as subduction. In a subduction zone, molten materials produced can rise to the surface of the earth and cause volcanic mountain building and earthquakes on the continental plate. For instance, after millions of years of the Nazca Plate sliding under the South American Plate, the Andes Mountains were formed. When two plates of the same type meet, the process of converging happens. When they are both oceanic plates, one plate slides under the other plate. An island group is often formed at this boundary. When both of the plates are continental, the plates push against one another, forming mountain ranges. For example, millions of years ago when the Indo-Australian Plate crashed into the Eurasian Plate, the earth s highest mountain range, the Himalayas, was formed. Lastly, when plates slide or grind past one another along faults, the process of faulting occurs. A well known example of this process is the San Andreas Fault in California.

10 Volcano Explanation. The plate tectonic theory has been used in an attempt to explain many processes affecting the earth, like volcanic eruptions. Most volcanic eruptions happen along plate boundaries. There is a circle of volcanoes surrounding the Pacific Ocean known as the Ring of Fire. This ring includes the Cascades in North America, the islands of Japan and Indonesia, and the Andes in South America. The theory also attempts to explain how volcanic island arcs, or chains of islands, are formed far away from a plate boundary. Hot Spots are hot regions deep inside the mantle of the earth that make columns of magma that rise above the surface of the earth. As the molten rock rises from a hot spot, the water underground may be heated by the magma and produce hot springs or geysers like the ones in Yellowstone National Park or in Iceland. If molten rock flows out of a crack in the surface of the earth, it may create a volcanic island chain as plates drift over a stationary hot spot. For instance, the easterly island of Hawaii is part of an island arc that is formed in the middle of a plate. Hawaii, which is over a hot spot, is always erupting. Since the Pacific Plate moved and removed the westward islands from the hot spot, they have remained dormant. Vocabulary: Geology- the study of the earth s surface and the processes that shape it, the connections between places, and the complex relationships between people and their environments. Core- the earth s center, consisting of very hot metal that is dense and solid in the inner core and molten, or liquid, in the outer core. Mantle- a thick layer of mostly solid rock beneath the earth s crust that surrounds the earth s core. Crust- the solid, rocky, surface layer of the earth. Lithosphere- the surface features of the earth, including soil, rocks, and landforms.

11 Atmosphere- the layer of gases, water vapor, and other substances above the earth. Hydrosphere- the water contained in oceans, lakes, rivers, and under the ground. Biosphere- the world of plants, animals, and other living things in earth s land and waters. Continent- any of the seven large landforms of the earth s surface: Africa, Antarctica, Asia, Australia, Europe, North America, and South America. Relief- the differences in elevation of the landforms in any particular area. Lava- magma, or molten rock form the earth s mantle, that breaks through the surface of the earth during volcanic activity. Fold- an area where rock layers have been bending and buckling. Fault- cracks in the earth's crust. Plate tectonics- the theory that the earth s outer shell is composed of a number of large, unanchored plates whose constant movement explains earthquakes and volcanic activity. Continental drift theory- the idea that continents slowly shift their positions due to movement of the tectonic plates on which they ride. Ring of Fire- An extensive zone of volcanic and seismic activity that coincides roughly with the borders of the Pacific Ocean. After reviewing the material in this lesson, please complete the Advanced World Geography Chapter 1 Lesson 2 Learning Check and Quiz.