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Transcript
Chapter 6 What is the structure of Earth? Crust-Earth’s outermost and thinnest layer Mantle-the layer that makes up most of Earth’s material Core-the center of the Earth The outermost and thinnest layer of the Earth is called the crust. There are two kinds of crust called continental crust and oceanic crust. When the continental crust dips below water it forms the continental shelf. The mantle is the layer that makes up most of Earth’s material. The top part is solid hot rock. The top part of the mantle and the crust above, make up the lithosphere. Convections currents flow slowly in the mantle. Cooler rocks flow down and hotter rocks flow up. The lithosphere floats on top of the convection currents. The center of the Earth is called the core. The inner core is solid. The outer core is liquid. The currents of the outer core make the Earth’s magnetic field. Scientists study the mantle and core by studying mantle materials that is pushed up through the cracks of the crust. Scientists study the Earth by measuring the vibrations from Earthquakes. A seismograph records earthquake waves. What causes earthquakes and volcanoes? Plate-a section of the lithosphere The lithosphere covers all of the Earth line a thin shell. It is broken up into several large pieces called plates. Earth’s plates are slowly moving. Small changes can cause mountains, while large changes can cause earthquakes. Mountains, earthquakes and volcanoes eruptions take place where the plates meet. The edges of plates are called plate boundaries. There are three types of boundaries. Converging boundaries are where two plates collide. Spreading boundaries form when plates move apart from each other. Sliding plate boundaries is when two plates move past each other in opposite directions. Destructive forces and processes wear away or tear down Earth features, such as earthquakes. Earthquakes most often occur on faults that are along plate boundaries. Faults are crakes in the Earth’s crust where the surrounding rock has moved or shifted. Earthquakes occur when the plates get stuck as they pass each other. The place where the plates start to slip is called a focus. The place on Earth’s surface above the focus is called an epicenter. Earthquakes can cause landslides, the downhill movement of large amounts of rock and soil. Earthquakes under the ocean can cause a tsunami, waves large enough to destroy things when they crash into a coastline. Most volcanoes form near colliding plate boundaries. As one plate moves below another plate, rock partially melts to make magma. Magma is force through to the surface through weak spots in the crust. Volcanoes that come from the ocean floor form volcanic islands when it reaches the surface of the water. What is weathering? Mechanical weathering-the breaking of rock into smaller pieces by forces Chemical weathering-the changing of material in a rock by chemical processes Weathering is the slow, destructive process that breaks rock into smaller pieces called sediments. There are two types of weathering. Mechanical weathering is the breaking of rock by forces. Chemical weathering is the changing of material in rock by chemical process. When water freezes in the cracks of rocks, it expands and forces rock to split apart, called ice wedging. Changes in pressure can cause rocks to break. Plant roots can grow into the cracks of rocks and break them. Raindrops that absorb carbon dioxide can dissolve parts of rocks. Fungi and other organism give off chemicals that change some rocks. Soil is usually made up of sediments, small bits from weathered rocks. Soil also contains decayed materials from organisms, gases from air, and water. Soils color varies, and color depends upon what materials are in the soil. What is erosion? Erosion is the movement if materials away from place to place. Gravity is the main force causing erosion, causing landslides and river flow. Water causes erosion. When water flow slows, the ability to move sediment lessens, and sediment is deposited, changing the shape of where it lands. Constant action of waves causes erosion and deposition on the coastline. Parts of the shoreline erode at different rates. Wind erosion is cause by wind blowing dust, soil, and sand from one place to another. Sand dunes are large, loose deposits of sand. Wind can blow topsoil off fields, making growth harder. How are minerals identified? A mineral is a naturally occurring solid that has a regular arrangement if particles in it. Minerals are found in soil and rocks. Properties include, smell, shape, and texture. To identify an unknown mineral, scientists compare observations with observations made of known minerals. How are rocks classified? Igneous-rocks formed when melted rock cools and hardens Sedimentary-rocks formed when layers of materials and rock particles settle on top of each other and then harden Metamorphic- a type of rock formed when existing rock is heated at high pressures and temperatures. When melted rock cools and hardens it forms igneous rocks. When layers of materials and rock particles settle on top of each other and then harden to form sedimentary rock. Plant and animal fossils are most often found in layers of sedimentary rock. Rock formed when existing rock is heated at high pressures and temperatures is called metamorphic rock. Rocks can change from one kind to another in any order, or stay the same for millions of years. Rock layers are put down in the order in which they are formed. Younger rock is at the surface of Earth. Scientists who study fossils, use location within layers of rock to determine age.