![](media/image1.png){width="0.5834645669291338in"
height="0.75in"}Caves, Canyons, Cactus & Critters

*Middle School Geology*

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Caves, Canyons, Cactus & Critters

Geology Curriculum

> **Wandering Continents** A study of plate tectonics. 23

1.  **Apples, Eggs, and the Earth** An activity designed to present\
    information on the layers of the Earth. 24

2.  **Come Visit Me In Tropical\... Antarctica?** Activity in which the
    supercontinent of Pangea is reconstructed using modern\
    continents, imagination, and a little help. 27

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**Wandering Continents**

Carlsbad was, at one time, located near the equator. Fossils of tropical
plants have been found in Antarctica. The same animals and rocks are
found on different continents. These, and many other pieces of evidence,
point to an earth that may not be as static as we would like to believe.
Throughout the past century, scientists looking at these, as well as
many other bits of information, have come to the conclusion that the
continents are moving. Research has shown that the floor of the Atlantic
Ocean is spreading in the middle. Seismology has found evidence of
large, convective plumes in the mantle that move the broken lithospheric
plates around like a conveyor belt.

Continents moving around on the surface of a planet are going to do some
damage. Colliding continents result in mountains as they crumple up. The
heat generated by the friction of their impact causes some of the rock
making up the continents to melt. This molten rock rises to the surface,
near the point of the collision, and creates a volcano. Continents
pulling apart result in basins. These basins sink below sea level and
are covered by water. Earthquakes are an obvious consequence of stresses
in the lithospheric plates as well.

The activities of this unit are designed to supplement classroom studies
of plate tectonics and their effect on the surface of the earth.

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**Apples, Eggs and Earth**

***What is the earth like inside?***

**Summary:** Students will use apples and hard-boiled eggs to model the
earth's internal structure.

**Duration:** One 50-minute class period

**Setting:** Classroom

**Vocabulary:** convection cell, crust, inner core, lithosphere, mantle,
model, Mohorovicic Discontinuity, outer core, plasticity

**Standards/Benchmarks Addressed:** SC1-E1, SC2-E2, SC2-E3, SC4-E1,
SC4-E5, SC6-E1, SC6-E8, SC12-E3

**Objectives**

Students will:

-   describe the earth's internal layers.

-   use apples or hard-boiled eggs to model the earth's internal layers.

**Background**

![](media/image4.wmf){width="1.4375in"
height="1.4270833333333333in"}What is the earth like inside? Is it all
magma? How do we know? Throughout history, there has been speculation on
what was really in the center of our planet. Some speculated that the
earth was a hollow sphere with an entire civilization living on the
inside. In 1864, Jules Verne wrote *Journey to the Center of the Earth*
in which the lost continent of Atlantis, dinosaurs, and a great deal of
adventure were found at the center of the earth. It was only in the past
century that we began to have any understanding of what was really in
the center of our planet.

It is only with the development of the science of seismology that we
have been able to peek at what lies beneath us. In 1909, a Yugoslav
scientist Andrija Mohorovicic discovered that seismic waves changed
speed somewhere between 32 and 64 kilometers beneath the earth's
surface. The *Mohorovicic Discontinuity*, as it came to be called,
marked the boundary between the earth's crust and the mantle. Subsequent
studies have shown the earth's interior to be composed of four major
layers: the crust, the mantle, the outer core, and the inner core.
Recent studies have shown that even these layers can be subdivided and
boundaries between them may not be as clearly defined as it was once
thought.

The earth's dense center is called the *inner core*. It has a radius of
approximately 1,300 kilometers and begins at a depth of around 5,150
kilometers. It is composed of nickel and iron. Temperatures in the inner
core reach 5,000^o^ C. This is well beyond the melting point of nickel
and iron. However, the intense pressure at the center of the earth
pushes the atoms of nickel and iron together so tightly that they remain
solid.

Around the inner core is the liquid *outer core*. It begins at a depth
of about 2900 kilometers and is around 2250 kilometers thick. The lower
pressures in this layer allow the nickel and iron to melt. However, the
temperatures are still high, ranging from around 2200^o^C in the upper
part to almost 5000^o^C near the inner core.

The layer directly beneath the earth's crust is the *mantle*. It is
composed mostly of the elements silicon, oxygen, iron, and magnesium.
Even though it is solid, the high temperatures and pressure allow the
solid rock to flow. This property is referred to as *plasticity.*
Temperatures range from 2200^o^C near the bottom to 870^o^C near the
top. Seismic research has indicated that the mantle contains great, slow
moving convection *cells*. In these cells, the hotter, less dense mantle
material rises toward the top while the cooler, denser material sinks
toward the bottom.

The thin, outermost layer of the earth is called the *crust*. It
consists mainly of the elements oxygen, silicon, magnesium, and
aluminum. Iron, calcium, sodium, and potassium are also abundant. The
thickness of the crust varies from 8 kilometers under the oceans to 70
kilometers under continents. The younger, denser areas of oceanic crust
are composed primarily of basaltic rocks and are thinner. The older,
less dense areas of continental crust are thicker and composed primarily
of granitic rocks.

The earth's crust and the upper part of the mantle compose the
*lithosphere.* The lithosphere is broken into large sections called
lithospheric plates. There are seven major plates and several minor
plates. Most plates contain both continental and oceanic crust. The
movement of these plates is called continental drift.

**Materials**

-   hard boiled eggs (one per group)

-   apples (one per group)

-   small sharp knives (one per group)

-   paper for drawing observations

-   crayons or colored pens

-   basketball

-   solid rubber ball

**Procedure**

***Warm up:*** Ask the students, "What is a *model*?" Discuss the ways
in which a model is built to a particular scale.

Hold up a basketball, a solid rubber ball, and an apple and ask the
students, "Which of these provides the best model of what the earth is
like inside?" List the reasons for their choice on the board or on an
overhead.

***Activity:*** This activity can be done in groups, or as a teacher-led
demonstration.

1.  Show the students a hard-boiled egg. Ask them to describe its parts
    to you. Discuss the fragile nature of the shell. Ask the students if
    they think the egg would be a good model of the earth.

2.  Gently tap the egg on a hard surface, trying to make it crack into
    large "plates." Describe the earth's crust to the students and
    introduce the idea of lithospheric plates. While doing this, outline
    the plates with a marker. Have the students draw what they observe.

3.  Using a sharp knife gently cut the egg lengthwise and show it to the
    students. Introduce the idea of the layers in the earth and describe
    each layer to the students. Be sure to point out that even though a
    single yolk represents the core, the earth actually has two layers
    at its core. Ask the students to list good and bad points of using
    an egg to model the earth's interior.

4.  Give each group an apple and a knife and have them do the following:

    a.  Slice the apple, top to bottom, into as many pieces, or wedges,
        as the group has students.

    b.  Have each student sketch his or her slice of apple on a piece of
        paper.

    c.  On their sketch, have the students label each of the layers in
        the apple with the name of the layer in the earth it represents.

    d.  For each layer, have students list its properties on the paper.

    e.  On the paper, have students list good and bad points of using an
        apple to model the earth's interior.

***Wrap Up:*** Allow students to eat their slice of the "earth."

Solicit suggestions from the students for other objects that could be
used to model the earth. For each, briefly discuss its good and bad
points.

**Assessment**

Have students:

-   turn in papers with sketches and answers.

-   list and describe each of the layers in the earth.

-   tell what characteristics make a good model.

**Extensions**

Have students design and build their own model of the earth's interior
using materials of their own choosing.

**Resources**

Coble, Charles, et al. 1993. *Prentice Hall Earth Science.* Englewood
Cliffs, NJ: Prentice Hall.

Ford, Brent. 1996. *Project Earth Science: Geology.* Arlington, VA:
National Science Teachers Association.

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**Come Visit Me in Tropical\... Antarctica?**

***Why are tropical plant fossils found in Antarctica?***

**Summary:** Students will use a map of the continents as they are today
and attempt to work backward to reconstruct Pangea.

**Duration:** One 50-minute class period

**Setting:** Classroom

**Vocabulary:** continental drift, sea-floor spreading, plate tectonics

**Standards/Benchmarks Addressed:** SC1-E1, SC1-E2, SC2-E1, SC2-E2,
SC4-E1, SC4-E5, SC5-E2, SC6-E1, SC6-E8, SC12-E3

**Objectives**

Students will:

-   describe evidence for the theory of continental drift.

-   explain the importance of continental drift in the formation of the
    Capitan Reef.

**Background**

![](media/image5.wmf){width="1.2291666666666667in"
height="1.3645833333333333in"} Have you ever taken a really close look
at a globe or a map of the earth and noticed that some of the continents
look as if they would almost fit together like the pieces of a jigsaw
puzzle? In the early 1900s, a scientist named Alfred Wegener did just
that. In fact, he went so far as to propose that the continents were
moving and had at one time been joined into a single large landmass. He
named this landmass Pangea, meaning, "all land." Prior to his death in
1930, he lacked the evidence to convince many of his theory. However,
since that time researchers have enough proof that Wegener's theory is
now widely accepted as accurate.

Among the pieces of evidence supporting the theory of continental drift
are the puzzle-like fit of the continents, fossil clues, climate clues,
and rock clues. Fossils of the same animal, a *Mesosaurus,* have been
found in both South America and Africa. The fossil fern, *Glossopteris,*
has been found in Africa, Australia, India, South America, and in
Antarctica. Other fossils have also been found on continents separated
by hundreds or thousands of miles of ocean water. Several hypotheses,
including continental drift, have been proposed to explain this.

Fossils of plants from much warmer climates have been found in
Antarctica and on Spitzbergen, an island in the Arctic Ocean.
Additionally, evidence of glaciation has been found in warm regions of
South America, Africa, India and Australia. Again, several hypotheses
have been proposed to explain this, one of which is continental drift.

Similar rock types and structures have been found in Africa and South
America. If you were to fit the two together like the pieces of a
puzzle, these layers would match. Mountains similar to the Appalachian
Mountains of the eastern United States have been found in Greenland and
western Europe. Again, if you were to fit the continents together like
the pieces of a puzzle, these mountains would match like one long chain.
Several hypotheses could be proposed, including continental drift.

Since the early 1960s, additional evidence has come from research
regarding the spreading of the Atlantic Ocean floor and actual
measurements of continental movement. Princeton University scientist
Harry Hess first suggested *sea-floor spreading*. However, it was not
until scientists aboard the research ship *Glomar Challenger* gathered
information from the rocks on the ocean floor that sea-floor spreading
was confirmed. Actual measurements have now been made that indicate the
exact direction, and speed, at which the continents are moving.

With confirmation of *continental drift*, a new theory called *plate
tectonics* was proposed. It states that the crust of the earth is broken
into plates that move around on the mantle. Included in the theory are
descriptions of the plates, the forces in the asthenosphere, part of the
upper mantle, that drive them, and what happens along the plate
boundaries.

**Materials**

-   Copies of continent maps (from this activity, or others you have
    copied from another source, including the continental shelf if
    possible) one per student

-   photos or pictures from magazines cut in a jigsaw pattern

-   scissors

-   paste (glue sticks are best)

-   paper

**Procedure**

***Warm up:*** Give each group of three or four students one of the
photos or pictures that has been cut up and tell them to reform the
image. After they are done ask what clues they used to help them.

Have the students look at a map that clearly shows all of the
continents. Ask if they think the continents look a little like a poorly
constructed jigsaw puzzle.

***Activity***

1.  Give the students copies of the continents sheet (or the continent
    maps you are providing).

2.  Instruct the students to cut out each continent and arrange them on
    a piece of paper as they are found today.

3.  Tell the students that they are to do their best to fit the
    continents together like a jigsaw puzzle. However, they cannot pick
    up a continent, they must slide them. They are not allowed to
    "leapfrog" over other continents. Suggest that they may want to
    close the Atlantic Ocean first, since South America and Africa
    obviously fit.

4.  Once they have the continents arranged as they believe that they may
    have been at one time, have them glue them onto the piece of paper.

***Wrap Up:*** As a class, discuss any difficulties the students had
fitting the continents together. Ask the students, "If the continents
were really together like this at one time, what evidence should I find
to support it?" Discuss all answers.

Lead a class discussion of Alfred Wegener's theory of continental drift
and the evidence that has been found since that time to support it.

**Assessment**

Have students:

-   submit their "continental" jigsaw puzzles.

-   describe evidence supporting the theory of continental drift.

**Extensions**

Have students conduct further studies regarding what happens at plate
boundaries. Focus on divergent, convergent, and transform fault
boundaries. Describe various surface features seen on the earth that
serve as evidence of these boundaries.

**Resources**

Feather, Ralph, et al. 1999. *Glencoe Earth Science.* Westerville, OH:
Glencoe/McGraw-Hill.

Ford, Brent. 1996. *Project Earth Science: Geology.* Arlington, VA:
National Science Teachers Association.

**Wandering Continents**

**Worksheet**

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