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Bellringer #27 • What is Geology? • List four things that geologists study. The Science of Geology • The Greek geo means Earth and logos means discourse. • Geology is the science that pursues and understanding of planet Earth. Areas of Geology • Geology is traditionally divided into two broad areas • Physical • Historical Physical Geology • Physical geology- examines the materials composing Earth and seeks to understand the many processes that operate beneath the surface. Historical Geology • The aim of historical geology, on the other hand, is to understand the origin of Earth and its development through time. • It is trying to establish an orderly chronological arrangement of the multitude of physical and biological changes that have occurred in the geologic past. • Physical geology precedes the study of Earth history because we must first understand how Earth works before we attempt to unravel its past. • To understand Earth is challenging because our planet is a dynamic body with many interacting parts and a complex history. • Earth is constantly changing. – Some of the changes are rapid and violent, as when landslides or volcanic eruptions occur. – Other changes are take place so slowly that it goes unnoticed. • A great deal of geology is based on observations and experiments conducted in the field. • Geology is also done in the laboratory where the study of various Earth materials provides information about many basic processes. • Geology requires an understanding of knowledge from physics, chemistry, and biology. • Geology is a science that seeks to expand our knowledge of the natural world and out place in it. Geology, People and the Environment • Many issues studied in geology are of practical value to people. • Natural hazards are a part of living on Earth. • Geologists study volcanoes, floods, earthquakes, and landslides. • These natural processes are only hazards when people try to live where they occur. Resources • Resources are another important focus of geology. • Resources include: – – – – Water Soil Metallic and nonmetallic minerals Energy • Geology deals with the formation, maintaining of supplies, environmental impact of their extraction and use. Human impact on the Environment • Rapid world population. – Gaining 100 million per year. • Negative impact on natural flooding • Clearing forests, building cities, and building dams • Changes to the environment that were meant to help society often has the opposite effect. Historical Notes • Aristotle believed that rocks were created under the “influence” of the stars and that earthquakes occurred when air crowded into the ground, was heated by central fires, and escaped explosively. Catastrophism • Mid-1600s • James Ussher, Irish Archbishop • Thought that Earth was only a few thousand years old (4004 B.C.) • His chronology (of human and Earth history) was printed in the margins of the Bible. • Catastrophists believed that Earth’s landscapes had been shaped primarily by great catastrophes. The Birth of Modern Geology • Began in the late 1700s when James Hutton, a Scottish physician and farmer, published his Theory of the Earth. • Hutton put forth a principle that is the pillar of geology today: uniformitarianism “The present is the key to the past.” • Physical, chemical, and biological laws that operate today have also operated in the geologic past. • The acceptance of uniformitarianism meant the acceptance of a very long history for Earth. • Earth’s processes may vary in intensity but they still take a very long time to be created or destroyed. • For example, mountains once existed in portions of present-day Minnesota, Wisconsin, and Michigan. • Today this regions consists of low hills and plains • The rock record contains evidence that shows Earth has experienced many cycles of mountain building and erosion. • The North American continent is being lowered at a rate of about 3 centimeters per 100 years. • It would take 100 million years for water, wind, and ice to lower mountains that were 10,000 feet high. Geologic Time • Radioactivity was discovered in 1896 • Using it for dating was first attempted in 1905 • We know dinosaurs became extinct about 65 million years ago. • The age of the Earth is about 4.6 billion years Relative Dating and the Geologic Time Scale • Relative dating- events are placed in their proper sequence or order without knowing their age in years. • Law of superposition- in layers of sedimentary rocks or lava flows, the youngest layer is on top and the oldest is on the bottom. • Sometimes the layers get turned upside down. Then the law does not work. • The Grand Canyon is a good example. The oldest rocks are located in the inner gorge and the youngest rocks are found on the rim. • So the law of superposition establishes the sequence of the rock layers but not their numerical age. Fossils • Fossils are the remains of prehistoric life. • Important in figuring out the geologic time scale. • Principle of Fossil Succession- fossil organisms succeed one another in order and therefore any time period can be recognized by its fossil content. • Without fossils, geologists lose their primary tool for subdividing geologic time. The Magnitude of Geologic Time • For most of us something or someone who is 90 years old is very old and a 1000 year old artifact is ancient. • When you think about Earth’s 4.6 billion year history, a geologic event that occurred 100 million years ago may be thought of as recent by a geologist, and a rock sample that has been dated at 10 million years may be called young. Homework • Define all of the vocab words for Chapter 21. • A list of the words can be found on page 765 • Please number your vocab. There are 21 words. Bellringer #28 • What are the three physical environments that the Earth is divided into? The Earth as a System • A system is a group of interacting parts that form a complex whole. • The Earth consists of rock, air, water and living things that all interact with each other. • Scientists divided this system into four parts: 1. The Geosphere (rock) 2. The Atmosphere (air) 3. The Hydrosphere (water) 4. The Biosphere (living things) 25 The Earth as a Integrated System 26 Atmosphere • The atmosphere is the mixture of gases that makes up the air we breathe. • It is very thin. • It is important: – It provides the air we breath – It protects us from UV radiation and heat • Nearly all of these gases are found in the first 30 km above the Earth’s surface Hydrosphere • The hydrosphere makes up all of the water on or near the Earth’s surface. • The ocean covers 71% of Earth • The ocean has a depth of 12,500 feet. • The hydrosphere includes freshwater found underground and in streams, lakes, and glaciers. • Water is also found in the atmosphere, on land, and in the soil Geosphere • The geosphere is the mostly solid, rocky part of the Earth that extends from the center of the core to the surface of the crust Biosphere • The biosphere is the part of the Earth where life exists. • It extends from about 9km above the Earth’s surface down to the bottom of the ocean. • The biosphere is therefore made up of parts of the geosphere, the atmosphere, and the hydrosphere. Chapter 21 Planet Earth Overview • This chapter discusses: – The composition of Earth’s interior – The theory of plate tectonics – The causes and classification of earthquakes and volcanoes – Types and properties of rocks and the rock cycle – Physical weathering, chemical weathering, and erosion. S.1 Earth’s Interior and Plate Tectonics • Focus – Earth’s geological layers – Plate tectonics – Types of plate boundaries and structures that form at each type • Vocab – – – – – – – Crust Mantle Core Lithosphere Plate tectonics Subduction Fault Key Ideas 〉How is Earth’s interior structured? 〉How has the appearance of Earth changed over time? 〉What geologic features are common near tectonic plate boundaries? What is Earth’s Interior Like? • We know that the Earth’s surface is solid because we walk on it everyday. • However, Earth is not solid all the way to the center. • Earth’s interior is made up of several distinct compositional layers. (three) • How do we know that? Discovering Earth’s Interior • Studying the Earth’s interior is not easy. • The deepest well that has been drilled into Earth’s interior is only about 12 km (7.7 miles) deep. – Kola Well in Russia 1970-1989 • An alternative method must be used to study the interior of the Earth. 35 Earth’s Interior Scientists use seismic waves to learn about Earth’s interior. Seismic waves are the same waves that travel through Earth’s interior during an earthquake. A seismic wave is altered by the nature of the material through which it travels. 36 Earth’s Interior Seismologists measure changes in the speed and direction of seismic waves that penetrate the interior of the planet. With this technique seismologists have learned that the Earth is made up of different layers and have inferred what substances make up each layer. 37 Earth’s Interior 38 • Scientists divide the Earth into different layers based on : –Composition- what it is made of –Physical Properties- any aspect of an object or substance that can be measured or perceived without changing its identity • Earth is divided the into three major layers: – crust – mantle – core 39 Crust • The crust is the thin and solid outermost layer of Earth above the mantle. • It is cooler than the interior of the Earth. • It is made up of hard, solid rock. • It is thin and makes up only about 1 % of the Earth’s mass. There are two kinds of crust • Oceanic Crust • Continental Crust Oceanic Crust • The crust beneath the ocean is called oceanic crust. • It has an average thickness of 5 to 8 km (3.1 to 4.9 miles). • Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. • Oceanic crust is primarily composed of mafic rocks, or sima. Mafic and sima what? • Mafic is an adjective describing a silicate material or rock that is rich in magnesium and iron. • Sima is the name for the lower layer of the Earth's crust. This layer is made of rocks rich in silicates and magnesium minerals. • Typically the sima when it comes to the surface is basalt, called the 'basalt layer' of the crust or 'basal crust' or 'basal layer' because it is the lowest layer of the crust. Age of oceanic crust. The red is most recent, and blue is the oldest. The age of oceanic crust as of 1995. The red is the most recent and blue is the oldest. Oceanic Crust Composition • Although a complete section of oceanic crust has not yet been drilled, geologists have several pieces of evidence that help them understand the ocean floor. • Estimations of composition are based on analyses of – ophiolites -sections of oceanic crust that are preserved on the continents. – comparisons of the seismic structure of the oceanic crust with laboratory determinations of seismic velocities in known rock types – samples recovered from the ocean floor by submersibles (midget submarines used by oceanographers), dredging, and drilling. • Oceanic crust is significantly simpler than ( continental crust and generally can be divided in three layers. Continental Crust • The continental crust is the layer of granitic, sedimentary and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. • Continental crust is thicker and less dense than oceanic crust. • Today continental crust is produced and destroyed mostly by plate tectonic processes The Crust – Earth’s Thin Skin Relative to its size, Earth's crust is about as thin as an apple's skin. This outermost layer is composed primarily of two types of rock. The continental crust is mostly granite. The oceanic crust is mostly basalt. Mantle • Mantle- the layer of rock between the crust and core. • Makes up 67% of the Earth’s mass. • 1,800 miles thick • Composed of rocks of medium density. • The uppermost 100km of the mantle is rigid. Along with the crust, it makes up the lithosphere (the plates). • The next layer, the asthenosphere, is solid, hot, and soft. It flows much like a glacier does. • The lower mantle is extremely dense. It, too, flows. Mantle Core • Earth’s interior gets warmer with depth • Earth’s core is nearly as hot as the surface of the sun. • Core: the center part of the Earth below the mantle • Made of the densest elements. • 33% of the Earth’s mass • Earth’s core is composed mainly of nickel and iron. It is said to be the size of Mars. • Radioactivity contributes to high internal temperatures – The breakdown of radioactive isotopes uranium, thorium and potassium give off energy that contributes to Earth’s high internal temperatures. – Temperatures in the mantle can reach more than 1250° C. – The core may reach temperatures above 5000° C. Homework • None • Chapter 21 Vocab Due Tomorrow Opening Activity • Work with the people at your table • Try to fit all of the cut out pieces together to form one large landmass. 55 Layers of the Earth 1. lithosphere the solid, outer layer of the Earth that consists of the crust and the rigid upper part of the mantle. • It is a cool, rigid layer that is divided into huge pieces called tectonic plates. Layers of the Earth 2. asthenosphere the solid, plastic layer of the mantle beneath the lithosphere. a. It is made of mantle rock that flows slowly, which allows tectonic plates to move on top of it. 3. Mesosphere - Beneath the asthenosphere is the lower part of the mantle. 57 Layers of the Earth 4. Outer core is a dense liquid layer. 5. Inner core a dense, solid inner core, made up mostly of iron and nickel. • Although the temperature of the inner core is estimated to be between 4,000°C to 5,000°C, it is solid because it is under enormous pressure. 58 Outer Core Inner Core • The outer core is molten...and so hot it could be as fluid as water. Its motions create Earth's dynamic magnetic field. • The inner core is under such immense pressure that it is solid metal. Five layers of Earth 60 • Alfred Wegner was born in Germany in 1880. • Astronomy degree in 1905. • A soldier in WWI. Developed the theory of continental drift while recovering from a war injury. • 1930, he went to Greenland to help establish a weather station. He took 4,000 pounds of supplies. He froze to death on the return journey. His theory was supported 30 years after his death. Plate Tectonics 〉How has the appearance of Earth changed over time? 〉Alfred Wegener hypothesized that all of the continents might have been part of one landmass in the past before they drifted apart. – Wegener pieced the continents together like a puzzle and called the supercontinent they formed Pangaea. – Wegener found nearly identical fossils on widely separate continents, which supported his idea. Fossil Evidence • Using fossil evidence, Wegner showed that 200 million years ago, the same kinds of animals lived on continents that are now oceans apart. • He argued that animals could not have evolved on separate continents. Mesosaurus bones discovered in Sao Palo, Brazil and western Africa. Then Now Plate Tectonics, continued • Evidence for Wegener’s ideas came later. – Wegener’s theory of continental drift was ignored until structures discovered on the ocean floor provided evidence for a mechanism for the movement of continents. – Symmetrical bands on either side of a mid-ocean ridge indicate that the two sides of the ridge were moving away from each other and new ocean floor was rising up between them. Plate Tectonics, continued • Alignment of oceanic rocks supports the theory of moving plates. – Iron in molten rock aligns itself with Earth’s magnetic field as it cools. – The Earth’s magnetic field reverses polarity about every 200,000 years. – The process is recorded as magnetic bands in rock, based on the age of the rock. – Symmetrical bands on either side of the Mid Atlantic Ridge suggest that the crust was moving away from the ridge. Plate Tectonics, continued • Earth has plates that move over the mantle. – The crust and upper portion of the mantle are divided into about seven large pieces called tectonic plates. • lithosphere: the solid outer layer of Earth that consists of the crust and the rigid upper part of the mantle • plate tectonics: the theory that explains how large pieces of the lithosphere, called plates, move and change shape Tectonic Plates The major tectonic plates include: 1. The Pacific plate 2. North America plate 3. South America plate 4. Africa plate 5. Eurasian plate 6. Antarctic plates 7. Nazca Plate 8. Indian plate 9. Australian plate 69 Plate Tectonics, continued • Scientists do not understand exactly what makes tectonic plates move. – One hypothesis suggests that plate movement results from convection currents in the asthenosphere, the hot, fluid portion of the mantle. – Another hypothesis suggests that plate movement results from the force of gravity acting on the plates. The diagrams show the break-up of the super continent Pangaea (meaning "all lands" in Greek). When Pangea existed, there was a huge ocean called Panthalassa. pan- all, thalassa- sea All that remains of Panthalassa today is the Pacific Ocean which has been decreasing in size ever since the breakup of Pangea. Homework • Using your knowledge from the notes today, answer the questions on the “Drilling into the Earth” worksheet. • Read the article “Inge Lehmann” and answer the questions on the sheet of paper with the questions. Bellringer# 29 • List the three layers of the Earth and their temperatures. • Use your book! Chapter 21 pg. 729 Plate Boundaries • Lithospheric plates move and all major interactions among the plates occur along their boundaries. – The border between two tectonic plates is called a boundary. • Volcanoes and earthquakes most often occur where tectonic plates come together. • At plate boundaries, many other dramatic features, such as mountains and rift valleys, can also occur. Types of Plate Boundaries • There are three different types of plate boundaries. • They are categorized by the type of plate movement. – Divergent plate boundaries – Convergent plate boundaries – Transform plate boundaries Divergent plate boundaries • A divergent plate boundary occurs where two plates move apart and create a gap between them. Divergent plate boundaries • Hot rock rises from the asthenosphere and cools to form new lithospheric rock. • The two diverging plates pull the newly formed lithosphere away from the gap. • The drop in pressure causes the asthenosphere to melt and form magma, which then forms new oceanic crust. (new rock forms) • Magma is liquid rock produced under Earth’s surface. Mid Oceanic Ridges • Mid-oceanic ridges result from divergent boundaries. • Mid oceanic ridges are mountain ranges at divergent boundaries in oceanic crust. • Mountains on land are formed by the folding of continental crust. Mid oceanic ridges are created by magma rising to the Earth’s surface and cooling. • Rift valleys occur along the center of a mid-oceanic ridge. • A rift valley is a narrow valley that forms where plates separate. • The most studied mid-oceanic ridge is the Mid-Atlantic Ridge. • Most of it is under water but it can be seen on land in Iceland. • New lithosphere is being added at the ocean ridges • So our planet should be getting larger • Right? Convergent plate boundaries • The Earth’s total surface area remains constant. • Older portions of the oceanic crust return to the mantle along Convergent plate boundaries. • Lithosphere is destroyed at convergent plate boundaries. There are three types of convergent plate boundaries 1. Oceanic plate collides with a Continental plate (EX: Andes Mountains) 2. Continental plate collides with a Continental plate (creates mountains EX: Himalayas) 3. Oceanic plate collides with a Oceanic plate (island formation) Subduction Plates slide over each other at a convergent boundary. The area where one plate slides over another is called a subduction zone. Subduction zones produce ocean trenches, mountains, and volcanoes. • Subduction: the process by which one lithospheric plate moves beneath another as a result of tectonic forces Oceanic trenches • Form between two oceanic plates or an oceanic plate and a continental plate. • They can be very deep. • The deepest is the Mariana Trench, located off the coast of Asia in the Pacific Ocean. • The deepest point is more than 6.8 miles beneath the ocean surface. "Grand Canyon of the Pacific", The Marianas Trench is the world's greatest ocean depth. The island of Saipan rises more than 36,000 feet above the floor of the trench. In the Pacific there is always an association between the arc of a chain of islands and deep ocean trenches. The southern islands are composed predominantly of limestone while the northern islands are composed of volcanic rock. The islands rise out of the sea in successive level terraces indicative of repeated volcanic elevations. Subduction of oceanic crust generates volcanoes Chains of volcanoes form on the upper plate in a subduction zone. These volcanoes can form far inland from their associated oceanic trench. Magma cools and over time the accumulation of rock forms chains of mountains and plateaus. Islands may form where two oceanic plates meet • When two oceanic plates meet: – The denser plate sinks beneath the less dense plate. – This forms a deep ocean trench – Magma is formed and rises to the surface to form a island arc. – An island arc is a chain of volcanic islands. • Ex: Islands of Japan form an island arc • Formed because of the subduction of the Pacific plate. Colliding tectonic plates create mountains • The Himalayas are the largest mountain range in the world. • The Indian plate and the Eurasian plate collided to form the mountains. • They are growing in both width and height. • The mountains grow several centimeters a year because the plates move slowly. • Mount Everest- tallest mountain with a peak at 29,035 ft above sea level. Transform Fault Boundaries • Plate movement can cause breaks in the lithosphere. • Fault- a break in a body of rock along which one block slides relative to another. • Faults can occur anywhere forces are great enough to break rock. • When rock moves horizontally at faults along plate boundaries, the boundary is called a transform fault boundary. • Plate movement at these boundaries causes earthquakes. • San Andreas Fault- runs from Mexico through California and out to sea north of San Francisco. • These boundaries can occur on land or on the ocean floor. Types of faults • There are four types of faults, each corresponding to the stress state that produces it. Reverse faults • Reverse faults are caused by compresional stresses, and are often found at convergent plate boundaries. Reverse faults are caused by compresional stresses, and are often found at convergent plate boundaries. Normal faults • Normal faults are caused by tension or extension and are often found at divergent boundaries Strike-slip faults • Strike-slip faults are caused by shear stress and are often found at oblique-slip or transform boundaries. Homework • Section 1 Review page 737 • Complete # 1-8