Journey to the Center of the Earth

Topic 12

Regents Earth Science

Objectives

• Describe the Earth’s internal structure.• Explain the changes in P and S wave

velocities in the Earth.• Describe the shadow zone and explain its

significance.• Use the ESRT to describe various

properties of the Earth’s interior such as pressure, temperature, and density.

The study of seismic waves allows scientists to “see” inside the earth.

Scientists have discovered that seismic waves

• refract

• reflect

• change velocity

• and become absorbed by various parts of the Earth’s interior

Changes in the speed of seismic waves were used to determine the location of the Earth’s different layers

Layers of the Earth

• Crust

• Mantle

• Outer Core

• Inner Core

Crust

• This is the layer that we live on

• The thickness ranges from 8 km under the oceans to 40 km under the continents

• Continental crust is thickest beneath high mountains

• It is the thinnest layer of the earth

Comparing Oceanic and Continental Crust

Oceanic Crust• Composition is

“basaltic”• Density about 3.0

g/cm3

• Younger (180 my old or less)

Continental Crust• Composition is

“granitic”• Density about 2.7

g/cm3

• Older (4 by old)

Mohorovicic Discontinuity

• Called Moho

• Is the boundary between the crust and mantle

• Was discovered in 1909 by Andrija Mohorovicic

• He found that seismic waves increase in speed at an average depth of 40 km.

The Mantle

• Is divided into 2 regions

• It consists of magnesium, iron, and silicon

• It is 3000 km wide

• It is more rigid closer to the surface

The Upper Mantle

Rigid Mantle• Cool and brittle• The rigid mantle and

crust make up the lithosphere

• Divided into sections called plates

• 15-300 km thick

Plastic Mantle• Partially molten - the

rock in this layer has the ability to flow.

• Also known as the asthenosphere

• Magma originates here• About 200 km thick

The Outer Core

• liquid

• 2100 km wide

• consists of nickel and iron

• flow of iron creates the Earth’s magnetic field

How do we know the outer core is liquid?

• S-waves do not pass through this zone

• Shadow zone - no p-waves or s-waves received here

• 103° to 143° from focus

At the outer core

• Thers is a sudden decrease in p-wave velocity and

• S-waves disappear

The Inner Core

• solid

• consists of the metals nickel and iron

• temperature is 6,000° C

• width = 2,100 km

The Earth’s Interior

ESRT page 10

Selected Poperrties of the Earth’s Interior

• The x-axis shows the depth from bottom to top.

• As depth increases, pressure increases.

• 1 atmosphere = 14.7 psi or “normal” air pressure at sea level

• As depth increases, density increases.

Melting Point and Temperature

• As depth increases, temperature increases.

• What evidence can you see for a liquid outer core?