Inside the Earth Chapter 4 Section 1 p. 96 - 102 Vocabulary: 1. crust 2. mantle 3. core 4. lithosphere 5. asthenosphere 6. mesosphere 7. tectonic plate

The Composition of the Earth p. 96 Scientists think about physical layers of the Earth in two ways: by their chemical composition and by their physical properties. The Earth is divided into three layers – the crust, the mantle, and the core – based on the compounds that make up each of the layers. The less dense compounds make up the crust and the mantle, and the densest compounds make up the core.

The Crust p. 96 The outermost layer of the Earth is the crust. The crust is 5 to 100 km thick. It is the thinnest layer of the Earth. There are two types of crust – continental and oceanic. Both are made mainly of the elements oxygen, silicon and aluminum.

The Mantle p. 97 The layer of the Earth between the crust and the core is the mantle. The mantle is much thicker than the crust and contains most of the Earth’s mass. No one has ever visited the mantle. The crust is too thick to drill through to reach the mantle. In some places, like in this picture of an oceanic vent, mantle rock pushes to the surface, which allows scientists to the study the rock directly. Magma from the mantle flows out of the active volcanoes on the ocean floor. These underwater volcanoes have given scientists many clues about the composition of the mantle. The mantle contains more magnesium and less aluminum and silicon than the crust, and so it is more dense than the crust.

The Core p. 97 The layer of the Earth that extends from below the mantle to the center of the Earth is the core. Scientists think that the Earth’s core is made mostly of iron and contains smaller amounts of nickel, but almost no oxygen, silicon, aluminum, or magnesium. The core makes up about one-third of the Earth’s mass.

The Physical Structure of the Earth p. 98 - 99 Another way to look at the Earth is to examine the physical properties of its layers. The Earth is divided into FIVE physical layers – the lithosphere, asthenosphere, mesosphere, outer core and inner core. Each layer has its own set of physical properties.

The Lithosphere The outermost, rigid layer of the Earth is called the lithosphere. It is made of two parts: the crust and the rigid upper part of the mantle. The lithosphere is divided into pieces called tectonic plates. The Asthenosphere The asthenosphere is is a plastic layer of the mantle on which pieces of the lithosphere move. The asthenosphere is made of solid rock that flows very slowly.

The Mesosphere Beneath the asthenosphere is the strong lower part of the mantle, called the mesosphere. The mesosphere extends from the bottom of the asthenosphere to the Earth’s core. Mesosphere The Outer Core The Earth’s core is divided into two parts – the outer core and the inner core. The outer core is the liquid layer of the Earth’s core that lies beneath the mantle and surrounds the inner core. The Inner Core The inner core is the solid, dense, center of our planet that extends from the bottom of the outer core to the center of the Earth, which is about 6,380 km below the surface.

Tectonic Plates p. 100 Pieces of the lithosphere that move around on top of the asthenosphere are called tectonic plates. Think of the lithosphere as a giant jigsaw puzzle and the tectonic plates are the puzzle pieces. Notice that each tectonic plate fits together with the tectonic plates that surround it. Not all tectonic plates are alike. For example, the South American plate has an entire continent on it and has oceanic crust. The Cocos plate has only oceanic crust. Some tectonic plates, such as the South American plate, include both continental and oceanic crust.

A Tectonic Plate Close-Up p. 101 This tectonic plate consists of the upper part of the mantle and both oceanic crust and continental crust. The thickest part of this plate is the continental crust. The thinnest part is in the mid-Atlantic Ocean.

Mapping the Earth’s Interior p. 102 Although scientists have never drilled through the crust of the Earth, they have learned a great deal about the inside of the Earth by studying earth quakes. When an earthquake happens, vibrations called seismic waves, are produced. Seismic waves travel at different speeds through the Earth. Their speed depends on the density and composition of the material they pass through. Seismic waves travel faster through a solid than through a liquid. Scientists measure the distance and travel times of these waves to calculate the density and thickness of each physical layer of the Earth.

Layers of the Earth Song

Quiz Time! 1. Name and describe the three layers that make up the Earth. Crust is the outermost layer, 5 – 110 km thick, made up mainly of oxygen, silicon, and aluminum Mantle is the layer between crust and core, 2,900 km thick, denser than the crust, contains most of the Earth’s mass Core is the innermost layer, made up mostly of iron 2. What are the five physical layers of the Earth? lithosphere, asthenosphere, mesosphere, inner core, and outer core 3. True or False? The asthenosphere is the thinnest physical layer. False, the lithosphere is the thinnest layer

4. The part of the Earth that is molten is the A. crust B. mantle C. outer core D. inner core C 5. The part of the Earth on which the tectonic plates move is the A lithosphere B. asthenosphere C. mesosphere D. crust B

Science Humor… One student said to another… I studied geology in sixth grade, but the curriculum was too deep. When I took geology, I went through a metamorphosis. Now I dig the subject! We had a great teacher. The class rocked!