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Class Notes After class, review your notes and jot questions and memory joggers in the narrow column that help connect ideas listed in the notes section. When you're studying, you will look at these cues to help you recall the salient facts in your notes, so keep that in mind when you create your cues. Name: Class: Block: Date: Topic: Unit 2 A Review of our Earth Questions/Main Ideas/Diagrams Notes: What is a Geological Timescale? A scale of the history of the earth, supported by geological/archeological evidence. What are two ways that scientists can tell how old the earth is? Radiometric dating and Relative dating using fossils. What is Relative Dating of Fossils? Using The law of superposition to compare ages of fossils. What is radiometric dating? The use of isotopes (like carbon 14) to tell us the absolute date of a fossilized organism. How Old is the Earth? The Geologic Time Scale divides Earth’s history of 4.6 billion years into subgroups that arrange events more orderly. The divisions are from largest to smallest length of time Eon era period epoch What might cause a major extinction? A catastrophic event might cause a major extinction, like the dinosaurs. What are some catastrophic events? Volcanoes Earthquakes Meteor showers Severe temperature changes (ice ages, global warming) Summary, Reflection, Analysis © 2004 AVID Center. All rights reserved. Page 1 Questions/Main Ideas/Diagrams: Notes: Structure and Composition The Earth is comprised of four distinctive systems Atmosphere Hydrosphere Biosphere Lithosphere At the center of the Earth is the core, which consists mainly of iron and is divided into 2 parts: Inner core Radius 1220 km 6000 oC Solid iron Outer core Liquid iron Radius 3480km Contributes to magnetic field The Mantle Next is the mantle a layer that makes up nearly 70% of Earth’s interior. It is composed primarily of oxygen, silicon and magnesium and is also divided into two parts: Asthenosphere- the solid, plastic layer of the mantle between the mesosphere (lower part of the mantle) and the lithosphere; made of mantle rock that flows very slowly which allows tectonic plates to move on top of it The Crust The crust is the top layer of the Earth. The upper mantle and the crust form the lithosphere (it is divided in to huge pieces called tectonic plates). Continental drift Alfred Wegener’s idea states continents have moved horizontally along Earth’s surface to their present positions Evidence that supports continental drift 1. Continents fit together like puzzle pieces. 2. Matching rock layers on Africa and South America 3. Matching fossils of land-based dinosaurs such as Mesosaurus in the southern region of both Africa and South America. Summary, Reflection, Analysis © 2004 AVID Center. All rights reserved. Page 2 Questions/Main Ideas/Diagrams: Notes: Plate Tectonics The lithosphere is broken into tectonic plates or lithospheric plates. Each plate is roughly 100km thick and consists of uppermost mantle with two types of crust on top: oceanic crust and continental crust. Oceanic crust is thin (5-10km) but dense – rich in iron, magnesium and silicon The continental crust is thicker (20-70km) and less dense consisting of primarily calcium, sodium, potassium and aluminum. Both types of crust can be found on a plate, but the denser ocean crust is found below sea level. Earth has 7 major plates and many minor plates. The places where plates meet are called the plate boundaries. Much of the geologic activity (earthquakes, volcanoes, mountain formation) takes place at the boundaries between tectonic plates. There are three different types of boundaries: 1. Divergent boundaries 2. Transform boundaries 3. Convergent boundaries Divergent Boundaries Divergent plates are where two plates move apart. This is also known as floor spreading. A rift occurs and magma moves up from the mantle and cools as it reaches the surface creating new crustal material. Mid Atlantic Ridge (causing Atlantic Ocean to grow larger) Convergent Boundaries Convergent plates are when two plates collide Crust is destroyed & recycled back into the interior of the Earth The denser plate (oceanic/basaltic) slides under the less dense plate (continental/granitic) Oceanic-Continental Convergence - When an oceanic plate pushes into and subducts under a continental plate, the overriding continental plate is lifted up and a mountain range is created. (oceanic is more dense and sinks) Summary, Reflection, Analysis © 2004 AVID Center. All rights reserved. Page 3 Questions/Main Ideas/Diagrams: Notes: Oceanic-Oceanic Convergence - When two oceanic plates converge one is usually subducted under the other and in the process a deep oceanic trench is formed (The Marianas Trench); also results in the formation of undersea volcanoes Continental-Continental Convergence - When two continents meet head-on, neither is subducted because the continental rocks are relatively light and, like two colliding icebergs, resist downward motion. Instead, the crust tends to buckle and be pushed upward or sideways. Transform boundaries Transform boundaries are where tectonic plates slide past each other along transform faults. Transform faults are a type of strike-slip fault which means that the movement of the fault is horizontal At times, movement along the fault is smooth and gradual. If friction prevents the rocks from sliding by smoothly, pressure builds up. This pressure or stress builds up to the point where it suddenly snaps, creating a earthquake. Earthquakes A fault is a break in the Earth’s crust along which blocks of the crust slide relative to one another The point within Earth where faulting begins is the focus, or hypocenter The point directly above the focus on the surface is the epicenter What are Seismic Waves? What causes earthquakes? Rocks in Earth’s crust is stressed and pulled This action stores elastic energy Once the build up of energy exceeds the strength of the rock the energy is released The energy is released as seismic waves Body Waves Two types of Body Waves: P and S P Waves (Primary waves) Compression waves since they push and pull rocks Summary, Reflection, Analysis © 2004 AVID Center. All rights reserved. Page 4 Questions/Main Ideas/Diagrams: Notes: Fastest moving seismic wave Able to move through solid rock and fluids S Waves (Secondary waves) Slower than a P wave Can ONLY move through solid rock A seismograph is used to detect seismic waves Measuring Earthquakes The Richter scale is a mathematical measurement of the intensity of the ground shaking, as measured on a seismograph. It is actually a measurement of the height (amplitude) of the waves produced by the earthquake. The Richter scale grows by powers of 10. An increase of 1 point means the strength of a quake is 10 time greater than the level before it. Here's how it works: An earthquake registering 2.0 on the Richter scale is 10 times stronger than a quake registering 1.0. A quake registering 3.0 is 10 X 10 or 100 times stronger than a quake registering 1.0 Earthquakes are measured by an instrument called a seismograph. The seismograph records the motion of the ground underneath it. By studying data from the seismograph, scientists can figure out exactly where and when the earthquake took place. They can also tell how big it was. The biggest earthquake ever recorded took place in Chile on May 11,1960. It measured 9.5 on the Richter scale and caused damage as far away as Japan. The world's second biggest earthquake, measuring 9.2 on the Richter scale, took place on Good Friday 1964 in Prince William Sound, Alaska. The Modified Mercalli scales measures how people feel and react to the shaking of an earthquake It is based on a series of key responses such as people awakening, the movement of furniture, and damage to structures. In general, the further one is from the epicenter of an earthquake, the less shaking is experienced. Summary, Reflection, Analysis © 2004 AVID Center. All rights reserved. Page 5 Questions/Main Ideas/Diagrams: Notes: Tsunamis Earthquakes which occur on the ocean floor produce giant sea waves called tsunamis. Tsunamis can travel at speeds of 700 to 800 km per hour. As they approach the coast, they can reach heights of greater than 20 meters. The Tsunami Warning Center is located in Hilo, Hawaii. Case Study: Sumatra On December 26, 2004 an earthquake originated in the Indian Ocean just off the western coast of northern Sumatra. It had the second largest magnitude recorded on a seismograph (9.1 and 9.3). The resulting tsunami killed over 200,000 people. The coast areas of Indonesia, Thailand, India and Sri Lanka were most affected. Why Volcanoes Occur Temperatures in the mantle are hot enough to melt rock into magma. Less dense than the solid rock around it, magma rises and some of it collects in magma chambers. As the magma rises, pressure decreases allowing trapped gasses to expand and propel the magma through cracks or fissures in the Earth’s surface causing an eruption. Erupted magma is called lava. Volcano Terms A vent is an opening through which eruptions take place. A crater is a basin like depression over a vent, at the summit of a volcano A caldera is a depression larger than the original crater (>1km. Diameter) that forms when the summit is blown off, or when the volcano collapses into the empty magma chamber. Example: Crater Lake atop Mt. St. Helens. Types of Volcanoes: Shield Volcanoes o Shield Volcanoes are built up almost entirely of lava flow, which pours out in all directions. o This results in a flat, conical shape that looks a little like a warrior's shield. Many of the world's largest volcanoes are Shield Volcanoes. o The Hawaiian Islands are a linear chain of them. Summary, Reflection, Analysis © 2004 AVID Center. All rights reserved. Page 6 Questions/Main Ideas/Diagrams: Notes: Types of Volcanoes: Stratovolcanoes (Composite) o Stratovolcanoes (also called Composite Volcanoes) are built up of alternating layers of lava flow, volcanic ash and cinders. o Stratovolcanes usually have large, steep sides and symmetrical cones. They can get to be as high as 8,000 feet. o Mt. Fuji in Japan and Mount St. Helens in the U.S. are Stratovolcanoes. o Types of Volcanoes: Cinder Cones o Cinder Cones are the simplest type of volcano. They are built up from blobs of lava ejected from a single vent. o Cinder Cones rarely get to be more than a thousand feet high. o Most famous cinder cone, Paricutin, grew out of a corn field in Mexico in 1943 from a new vent. Ring of Fire One major earthquake and volcano zone extends nearly all the way around the edge of the Pacific Ocean. This zone goes through New Zealand, the Philippines, Japan, Alaska and along the western coasts of North and South America. The San Andreas fault is part of this zone. Case Study: Mount St. Helens Located in Washington State, Mount St. Helens erupted in 1980. The earthquake removed trees, increased soil erosion, destroyed wildlife and polluted the air with gases and ash. Other effects included mudflows, melting of glacial ice and snow and clogged rivers that caused flooding. Fifty seven people were killed. Case Study: Mount Pinatubo Mount Pinatubo is part of a chain of composite volcanoes on the west coast of the island of Luzon in the Philippines. In June 1991, Mount Pinatubo erupted for 9 hours and vented 18 million metric tons of sulfur dioxide into the atmosphere which encircled Earth in three weeks after reaching the stratosphere. This was the largest sulfur dioxide cloud ever detected to date. Summary, Reflection, Analysis © 2004 AVID Center. All rights reserved. Page 7