CHAPTER 2 EARTH’S INTERIORSylvia Marquez

VOCABULARY

• Seismic waves-waves formed during an earthquake

• Granite-a rock usually is a light color and has coarse grains

• Outer core-is a layer of molten metal surrounding the inner core

• Pressure-force pressing on an area

P=F =force A=area

• Inner core-is a dense ball of solid metal

• Crust-the layer of rock that forms Earth’s outer skin

• Lithosphere-the crust and uppermost mantle

• Basalt-a dark, fine-grained rock

• Asthenosphere-part of the mantle just beneath the lithosphere, less rigid than the rock above. Over thousands of years this part of the mantle can bend like a metal spoon

HOW DO GEOLOGISTS LEARN ABOUT EARTH’S INTERIOR?

•Processes that affect Earth’s surface are often a result of what’s going on inside Earth. But what’s inside Earth? Geologists use two main types of evidence to learn about Earth’s interior: direct evidence from rock samples and indirect evidence from seismic waves.

EVIDENCE FROM ROCK SAMPLES

•Geologists have drilled holes as deep as 12.3 kilometers into Earth. The drills bring up samples of rock that give them clues about Earth’s structure and conditions deep inside Earth, where the rocks formed. In addition, volcanoes sometimes blast rock to the surface from depths of more than 100 km. These rocks provide information about Earth’s interior.

•Also, in laboratories, geologists have re-created conditions inside Earth to see how rock behaves. They use laser beams on pieces of rock while squeezing the rock with great force, to find out how elastic rocks are. They do this to show how rocks behave under great pressure.

EVIDENCE FROM SEISMIC WAVES

•Geologists also use an indirect method. When earthquakes occur, they produce seismic waves. Geologists record the waves and study how they travel through Earth. The speed of seismic waves and the paths they take give geologists clues about the structure of the planet. The paths of these waves reveal areas inside Earth where the makeup or form of material changes. To better understand how this works, let’s see a video.

HTTPS://WWW.YOUTUBE.COM/WATCH?V=AY6SG7GPALO

Click icon to add picture

ASSESS• Other than rock. What do you think you can find below the

surface of Earth?• How did geologists gather information from the interior of

our planet?• What direct evidence of Earth’s interior do geologists use?• What limitation do geologists have when studying Earth’s

interior?• How did the behavior of the waves “show” the location of

different layers on Earth’s interior?

FEATURES OF EARTH’S CRUST, MANTLE, AND CORE

• The layers that make up Earth vary in thickness, composition (the elements that make them up), and pressure (the amount of force pressing on them).• Scientists know that Earth’s interior is made up by three main layers, and each one covers the layers beneath it, like the layers of an onion.

The three main layers are: Crust-a layer of solid rock

that includes both dry land and the ocean floor

Mantle-is made out of rock that is very hot, but solid.

Core- made mostly of the metals iron and nickel, but it also has oxygen, sulfur, and silicon

•Each layer has its own characteristics, some of them apply throughout all of Earth. For example, the deeper inside Earth, the greater the mass of the rock that is pressing down from above.•Pressure results from a force pressing on an area because of the weight of the rock above, pressure inside Earth increases its depth. The deeper down inside Earth, the greater the pressure.

•The mass of rock that presses down from above affects the temperature inside Earth. The temperature inside earth increases as depth increases.•Beneath Earth’s surface, the surrounding rock is cool, but a 20 meters down, the rock starts to get warmer.•For every 40 meters of depth from that point, the temperature typically rises 1 Celsius degree

CRUST• The layer of soil where you step on is called crust• The crust is a layer of solid rock that includes both dry land and the ocean floor• The main elements in the crust are oxygen and silicon• It’s thinner than the layer that lies beneath it• In most places, the crust is between 5 and 40 km, thick

• It is thickest under high mountains-where it can be as thick as 80 km.-and thinnest beneath the ocean• The crust beneath the ocean is called oceanic crust• Its overall composition is much like basalt, with small amounts of ocean sediment on top• The crust that forms continents is called continental crust, it contains many types of rocks•Unlike oceanic crust, its composition varies greatly, but it is mostly formed by granite

•What percent of the crust is iron?•Which element makes up 2.6 percent of the crust?• In total, how much of Earth’s crust is made up of oxygen and silicon?•What is temperature?•What general statement can you make about the change in temperature through Earth’s interior?•What general statement can you make about the change in pressure inside Earth?•Why does temperature increase the deeper you go?•Which type of crust is thicker?• Is it possible for solid rock to flow?

ASSESS: CREATE A TABLE COMPARING THE TWO TYPES OF CRUST BY FILLING THE INFORMATION REQUIRED

Oceanic Crust

• Typical rock:_________• Relative grain size:_________• Color:_________• Thickness:_________• Forms:________

Continental Crust

• Typical rock:__________• Relative grain size:__________• Color:________• Thickness:__________• Forms:_________

MANTLE

About 40 km. beneath dry land, the rock in Earth’s interior changes. The rock contains more magnesium and iron than rock above it. The rock below the boundary is the solid material of the mantle, a layer of hot rock. The mantle is made of rock that is very hot, but it’s still solid. Scientists divide the mantle into layers based on the physical characteristics of each layer. Overall, the mantle is nearly 3,000 km. thick.

LAYERS OF THE MANTLELithosphere

*Below the crust

*Brittle rock, like the crust

*Uppermost layer

*Strong, hard, rigid

*Averages about 100 km. thick

Asthenosphere

*Below the lithosphere

*Hotter and under increasing pressure

*Less rigid than rocks above

*Over thousands of years this part can bend like a metal spoon

*If you kicked it, it will stub your toe

*Softer than the lithosphere

Mesosphere

*Beneath the asthenosphere

*It’s hot but more rigid because of high pressure

*It includes a region called the transition zone, which lies beneath the asthenosphere

*It includes the lower mantle, which extends down to Earth’s core

MANTLE

COREBelow the mantle lies Earth’s core. It is made mostly of the metals iron and nickel. It consists of two parts-a liquid outer core and a solid inner core. The outer core is 2,258 km. thick. The inner core is a solid ball. Its radius is 1,222 km. The total radius of the core is 3,480 km. The core occupies the center of the planet.

Outer Core

• A layer of molten metal surrounding the inner core• Despite enormous pressure,

it’s liquid • It’s made of iron and nickel,

but it also contains oxygen, sulfur, and silicon

Inner Core

• A dense ball of solid metal• Extreme pressure squeezes

the atoms of iron and nickel so much that they cannot spread out to become liquid• It’s made of iron and nickel,

but it also contains oxygen, sulfur, and silicon

QUESTIONS

•Why is the asthenosphere different from the lithosphere?•How does the inner core differ from the outer core?•Why do you think geologists consider the inner core and the outer core as part of the same layer?•How does the thickness of continental crust and oceanic crust compare?•Which of earth’s layer is the thickest?•Which is the thinnest?

VENN DIAGRAM

Inner Core Outer CoreBoth

THE CORE AND EARTH’S MAGNETIC FIELD

• Scientists think that movements in the liquid outer core create Earth’s magnetic field• The planet acts like a giant bar magnet because of the magnetic field• The magnetic field affects the whole planet•When you use a compass, its needle aligns with the lines of force on Earth’s magnetic north pole, which is not the same location as Earth’s geographic North Pole

SUMMARIZEThickness/Radius Composition Solid/Liquid

Crust 5-80 km. Granite/basalt

solid

Mantle 2,811-2,886 km.

Hot rock solid

Outer Core

2,258 km. Iron/nickel liquid

Inner Core 1,222 km. Iron/nickel solid

TOTAL 6,371 km.

ASSESS

•On a piece of paper, draw each of Earth’s layers. Include the outer core and the inner core. Label each layer ; then color it using different colors for each layer.