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As you go deeper into the earth:
1) The materials it's made of changes
2) The materials increase in density
3) The temperature and pressure increase 

Earth's layers can be classified in different ways.

Here they are classified by physical properties. (Are they hot or cold / liquid or solid?)

They are also classified by what they are made of.

Layers by Physical Properties

Lithosphere - cool, solid
Asthenosphere - soft and flowing rocky material 
(convection is happening  here)
Mantle - solid (because of the high pressure there)
Outer Core - liquid
Inner Core - solid

Layers by Their Composition

Crust - rocky silicates (5 - 50 km thick)
Mantle - denser rocky silicates (2900 km)
Core - very dense, metals - iron and nickel (3400 km)

The diagram on the right is arranged by what the layers are made of.
The outer layer of the earth is the crust.  This layer is similar to the skin on an apple.  The crust of the Earth is like a skin made of rock that covers the entire planet.  The skin is made up of two parts, the continents and the ocean floor.  The crust is thickest over the continents-from twenty to thirty-five miles thick-and thinnest on the ocean floor-around three to five miles thick.  The crust floats on a layer of melted rock and metal called the mantle. The core is at the very center of the earth.
The crust of the earth is made up of rocky material.  The mantle is made up of much denser rocky material. The core of the earth is made up of the metals, nickel and iron.

The crust is made up of three different kinds of rocks.  Each kind of rock is formed in a different way.  Igneous rocks are formed when melted rock inside the crust cools. As the rock cools, it becomes hard.  Usually this rock is formed from volcanoes.  Sedimentary rocks are formed when material is eroded by water and weather. This material settles and hardens.  Sedimentary rock may contain fossils.  Metamorphic rocks form from a change.  Heat and the weight of the earth's crust change igneous and sedimentary rocks into metamorphic rocks.

Soil is found on the crust.  It is made from the breakdown of rocks and the decay of dead organisms. Soil nourishes plants and contains living things.

The diagram on the left is arranged by how the layers behave (their physical properties).
The lithosphere is cool and solid. We live on the lithosphere.
The asthenosphere is soft and flowing.  It is also hot.
The mantle is solid. It is hotter than the layer above it, but solid because the pressure there is so high.
The outer core, which is hotter than the layer above it, is liquid.
The inner core, which is much hotter than the outer core, is solid due to its intense pressure.

How do scientists know what the interior of the earth is like?   Answer: SEISMIC WAVES which are caused by earthquakes.
There are P waves and S waves.  S waves do not travel through liquids.
Rock density influences the speed of the seismic wave.
Seismic waves are refracted (curved).  Look at the following pictures.  Listen to the discussion.
Earthquake waves are measured with the Richter Scale
Meteorites that reach the earth also help us infer what the earth's interior is like.
Scientists think that meteorites are the cores of planets that have broken up long ago.
Meteorites are composed of nickel and iron.  So...
We think that our earth's core is also made up of nickel and iron.

Because the crust floats on the mantle, movement occurs between different parts of the crust.  This movement creates forces that sometimes cause earthquakes and volcanic eruptions.  The entire crust is made up of plates called tectonic plates.  As these plates float on the mantle, theu sometimes brush or bump into each other.  This kind of movement causes earthquakes.  When the plates float away from each other, they leave gaps or vents, through which melted rock (magma) from the mantle seeps or gushes to the surface.  This movement of melted rock to the surface is a volcanic eruption.

Evidence for the theory of Plate Tectonics:
    Shape of the continents - they seem to fit together

There is fossil evidence that continents were once together.
There is rock evidence that continents were once together.
There is glacier evidence that continents were once together.

Sea floor spreading - the mid-ocean ridge is a huge crack in the crust where the hot mantle pushes upward. Pieces of the crust on each side of the crack move away from each other.  Molten rock from the mantle wells up, forming new crust.
Old crust is being swallowed up in ocean trenches at the same time so the ocean bottom is recycled every 300 million years.

Theory of plate tectonics - the lithosphere of the earth is divided into plates which are constantly moving.

Plates meet at boundaries

Plates can be convergent (plates come together)
Plates can be divergent (plate move away from each other)
Plates can have transform faults (plates slide past each other)

This causes earthquakes and volcanoes, as well as mountain building.  Earthquakes, volcanoes, mountains occur at plate boundaries.

Convection in the mantle makes the plates move.

The earth's surface can change abruptly as a result of earthquakes and volcanic eruptions.  These changes have an impact on people.   Every year people lose their homes and their lives because the crust of the earth shifts and changes, destroying everything in its path.  In the early 1900's almost the whole city of San Francisco was destroyed by an earthquake.  In the late 1980's, another earthquake hit San Francisco.  Again many lives were lost, not to mention the homes and workplaces that are gone forever.  The state of Alaska has been badly damaged by earthquakes.  Japan and Korea are often victims of this powerful force.  Erupting volcanoes have destroyed entire cities and the people living in them.  Some of the most important fossils ever found are those made by the people who lived in Pompeii and Herculaneum in A.D. 79 when they were covered with volcanic ash and lava as Mount Vesuvious erupted, completely covering the two Roman towns.

Sometimes, however, the Earth builds up instead of tearing down as it changes.  Many mountain ranges have been pushed up out of the earth as tectonic plates brushed past one another and earthquakes occurred.  Many islands in the ocean have been built up as a result of volcanic eruptions.  The Hawaiian Islands formed when volcanoes erupted.  The melted rock boiled through open spaces in the crust.  Then it came in contact with the ocean, which cooled and hardened it. With each eruption, more rock was added until the islands were above sea level.  Gradually the rock broke down into soil and plants began to grow.  Through its mightly forces, the Earth can be destructive, but it also can be constructive.

1. What is the outer layer of Earth? _____________________________________________________

2. How thick is the crust? ____________________________________________________________

3. How does the crust rest on the Earth? ________________________________________________


4. What kinds of rock make up the outer layer of the earth.  How is each type formed? _____________



5. What are the two major forces that change the shape of the earth's crust? ______________________


6. Describe the force that causses an earthquake? _________________________________________



7. What force causes a volcanic eruption? _______________________________________________



8. How do earthquakes and volcanic eruptions affect the people who live near them? _______________




Discuss the Richter Scale.

FOR THE GEPA: The state says you need to know the following:
A student should know that:

    1. Dynamic forces change the earth's surface by building up or wearing down.
    2. New features on the earth's crust are formed as a result of dynamic forces.
    3. The earth's surface can change abruptly as a result of earthquakes and volcanic eruptions or the earth's surface can change more slowly as a result of erosion, glaciation, and weathering.
    4. Forces that uplift the earth's surface include volcanism which forms mountains and volcanoes.
    5. Forces that wear the earth's surface down include weathering, glaciation and erosion.  Features formed as a result of these forces include soil and valleys.
    6. Each of these changes has an impact on people.
    7. Fossils provide evidence that life and environmental conditions have changed.