Introduction 
The theory of plate tectonics states that the Earth’s lithosphere is broken into 15 major plates and that move on the top of the hot plastic upper mantle, known as the asthenosphere. This theory also says that these plates are in motion as a result of convection in the asthenosphere, creating a variety of interactions at the plate boundaries. At the plate boundaries, plates may converge (collide), diverge (separate), or slide past each other (transform boundary).  In addition, some plates may appear to be inactive. The purpose of this lab is to demonstrate the different types of interactions at plate boundaries.

Materials
graham crackers
Rice Krispy treat                                                                 
Frosting/Marshmallow Fluff
water
plastic spoon
paper plate

Procedure 
Part 1: Divergent Plate Boundaries
Part 2: Convergent Plate Boundaries (Continental and Oceanic)
Part 3: Convergent Plate Boundaries (Continental)
Part 4: Transform Plate Boundaries

Watch the video below before following the procedure for each plate boundary.  You will be given permission to enjoy your tectonic plates with your partner only after Ms. Shon has signed your station packet.  Have fun!

Part 1: Divergent Plate Boundaries 

Procedure:
1.  Divide your plate into four sections with a pencil/pen (see picture on the right)
2.  Take two graham cracker pieces.
3.  Using the spoon, spread a thick layer of frosting in one quarter of your paper plate. It should be about the size of both graham crackers, and about equally thick.
4.  Lay the two pieces of graham cracker side by side on top of the frosting so they are touching.
5.  To imitate the result of diverging oceanic plates, press down on the crackers as you slowly push down and apart in opposite directions. 

Part 2: Convergent Plate Boundaries (Continental and Oceanic) 

Procedure:
1.  Take one new graham cracker. This represents the thin but dense oceanic plate.
2.  Spread a thin layer of frosting on another quarter of your paper plate. 
3.  Take one Rice Krispy treat and lay it next to the graham cracker so they are almost touching, end to end. The Rice Krispy treat represents the thicker but less dense continental plate.
4.  Push the two “plates” slowly toward each other and observe which plate rides up over the other. On the actual surface of the Earth, the oceanic plate is subducted.

Part 3: Convergent Plate Boundaries (Continental and Continental) 


Procedure: 
1.  Take two new graham crackers.  Each piece of graham cracker represents a continental plate.
2.  Spread a thin layer of frosting on another quarter of your paper plate.
3.  Dip one end of each of the two graham crackers into a cup of water.  See picture.
4.  Immediately remove the crackers and lay them end to end on the frosting with the wet edges nearly touching.
5. Slowly push the two crackers together.

Part 4: Transform Plate Boundaries (Continental) 

Procedure:
1.  Take two graham cracker pieces.
2.  Spread a thick layer of frosting on the last quarter of your plate.
3.  Lay the two pieces of graham cracker side by side on top of the frosting so they are touching.
4.  Place one hand on each of the graham cracker pieces and push them together by applying steady, moderate pressure. At the same time, also push one of the pieces away from you while pulling the other toward you. If you do this correctly, the cracker should hold while you increase the push-pull pressure, but will finally break from the opposite forces.

While new ocean crust is constantly being created at mid-ocean ridges, old crust must either be destroyed or reduced at the same rate (or else the surface of the Earth would be growing).  On the other hand, when two continental plates ram into each other, they crumple and fold under the enormous pressure, creating great mountain ranges. 

The highest mountain range in the world, the snow-capped Himalayas, is an example of a continent-to-continent collision. This immense mountain range began to form when two large landmasses, India and Eurasia, driven by tectonic plate movement, collided. Because both landmasses have about the same rock density, one plate could not be subducted under the other. The pressure of the colliding plates could only be relieved by thrusting skyward. The folding, bending, and twisting of the the collision zone formed the jagged Himalayan peaks. This string of towering peaks is still being thrust up as India, embedded in the Indo-Australian Plate, continues to crunch relentlessly into Tibet, on the southern edge of the Eurasian Plate.

Extension Activity
BrainPop: Mountains
Username = ms881
Password = ms88rocks

Earth's crust and the upper part of the mantle make up the lithosphere. The lithosphere is separated into tectonic plates that float on top of the molten asthenosphere. The tectonic plates are constantly moving together (convergent boundary), apart (divergent boundary), and past each other (transform boundary). This phenomenon is known as the theory of plate tectonics.

The theory of plate tectonics also explains how Earth’s lithosphere is recycled over time. Tectonic plates are destroyed at subduction zones.  Subduction zones are areas where a denser plate slides beneath a less dense plate. The denser plate sinks back into the Earth's hot mantle, then melts. New oceanic crust is formed at mid-ocean ridges.  This happens through the process of seafloor spreading.

Mid-ocean ridges are divergent plate boundaries.  At mid-ocean ridges, tectonic plates move apart and seafloor spreading occurs.  Seafloor spreading is the process by which new oceanic lithosphere forms at mid-ocean ridges.  As tectonic plates move away from each other, magma rises from Earth’s interior.  It then cools and solidifies in the center of the ridge. The rising magma pushes up between the plates and drives them further apart.

As new crust is forming at the spreading center, it pushes the older crust apart. Because of this, the oceanic crust contains symmetrical patterns of crustal rock ages. These rocks increase in age as their distance from the mid-ocean ridge increases.

Extension Activity
BrainPop: Ocean Floor
Username = ms881
Password = ms88rocks

Extension Activity II
Ocean Explorer: Mid-Ocean Ridges

What is a volcano?
A volcano is an opening in Earth’s crust through which magma rises.  Magma is called lava once it reaches the Earth’s surface.  Volcanoes form on land, in the ocean, and at the center of islands, but are most commonly formed in the ocean.  A number of factors contribute to the formation of a volcano. 

How do volcanoes form?
All volcanoes begin as magma. The magma forms when rock material melts, or becomes molten, close to where the mantle and crust meet.  Molten material contains gases.  Under intense pressure, the gases remain dissolved. As the molten material rises to Earth’s surface, the pressure decreases.  When this happens, the gases separate from the liquid magma.  This process is similar to opening a can of soda.  When the cap is removed, gases escape the can of soda.  Gases in the magma include water vapor, carbon dioxide, sulfur, chlorine, and fluorine.  As these gases expand, they produce an explosion eruption of lava at Earth’s surface. 

Volcanoes at Divergent Boundaries
Most volcanic activity occurs in the ocean along divergent plate boundaries.  Magma rises from the Earth’s mantle, moving oceanic plates apart.  When the magma cools, it turns into new crust.  This process creates mid-ocean ridges, which are under-water mountain ranges.

Extension Activity
BrainPop: Volcanoes
Username = ms881
Password = ms88rocks

What causes Earthquakes?
Tectonic plate movement is the primary cause of earthquakes.  Tectonic plates do not have smooth edges, and generate a ton of friction when they slide/grind past each other at a transform boundary.  The edges can become stuck for a while, too.  If this happens, pressure builds up in the crust. The pressure can build and build until the rocks snap, releasing seismic waves. The sudden release of these seismic waves is called an earthquake. 

Earthquakes tell us about the Earth's Interior Structure
Because P and S waves travel at different speeds and through different types of materials (S waves cannot travel through solids), scientists were able to determine that the Earth had 4 layers.  Since the S waves could not travel through the liquid outer core, the waves cannot travel through to the other side of the Earth.

1.  Measure the thickness of each layer in centimeters.
2.  Create a scale for each layer by making the number of centimeters of each layer equal to the number of kilometers of each layer in the ACTUAL interior of Earth.
3.  Calculate the scale factor each layer by dividing the number of centimeters in each layer (from the model) by the number of kilometers in each layer (of actual Earth).
4.  If the scale factor is the same for each layer, then the model is to scale!  If the scale factor is NOT the same for each layer, then the model is not to scale.

The density of a material can be found by measuring its mass (g) and volume (mL for liquids, cm3 for solids), then dividing the mass by its volume.  But can the density of a material change?  Below we will address this question by determining of shape, size/amount, or temperature can change the density of a material.

As we have observed, a material that is more dense than the material around it will sink.  Material that is less dense than the material around it will float. This explains why the Earth layers in the way that it does!  The most dense layer (inner core) "sinks", while the least dense layer (crust) "floats"!

Since the mass and volume both do not change when re-shaping the clay, the density does not change.  Even though it may seem as if the clay is more compressed (tightly packed) in the oval than in the hollow square, the spacing between those tiny particles that make up the clay is constant (does not change).  Therefore, the shape of a material/substance does not affect its density.

2.  Does size (or amount) affect density?
Dr. OPHERC holds two different amounts of molasses that came from the same jar.  Does the amount of molasses affect its density?

Again, in order to answer this question, we simply need to measure the mass and volume of the molasses at each amount.

The mass and volume both change when changing the amount of molasses.  However, the density does not change.  This is because the mass and volume increase at the same rate/proportion!  Even though there is more molasses (mass) in test tube A, the molasses also takes up more space (volume).  Therefore, the spacing between those tiny particles that make up the molasses is constant (does not change).  In other words, the size or amount of a material/substance does not affect its density.

3.  Does temperature affect density?
If we heat or chill the same amount of water, then does the density of the water change?  Fairly measuring the mass and volume of the water (in order to address this question) is a bit more challenging, because water evaporates when heated, thus affecting both the mass and the volume of water being measured.

Check out the video below on "lake stratification" in order to learn more about how temperature affects the density of water (and other materials).

Assignment
Complete the assignment on Google Classroom.

Continental Drift
About 100 years ago, German scientist Alfred Wegener noticed that the coasts of western Africa and eastern South America matched up like pieces of a jigsaw puzzle.  Although he was not the first to notice this, Wegener was the first to formally present evidence suggesting that the two continents had once been connected.  Wegener's hypothesis was called "continental drift".  

Wegener was convinced that the two continents were once part of an enormous super-continent called Pangaea, meaning “all earth,” that split apart over hundreds of millions of years.  He knew that the two areas had many geological and biological similarities. For example, fossils of the ancient reptile mesosaurus are only found in southern Africa and South America.  Mesosaurus, which lived in  freshwater lakes and rivers, was only about one meter long and would not have been able to swim across the salty Atlantic Ocean.   

Wegener also used climate clues as evidence to support his hypothesis (claim) of continental drift. Fossils of warm-weather plants had been found on the island of Spitsbergen in the Arctic Ocean. Wegener explained that Spitsbergen likely "drifted" from warmer, tropical regions.  In the same way, glacial deposits and rock surfaces polished and marked by glaciers are found in warm regions where glaciers do not exist, such as South America, Africa, India, and Australia.  Wegener argued that these continents were likely connected and partly covered with ice near Earth's south pole a long time ago.

Plate Tectonics
For a very long time, other scientists did not accept Wegener’s theory of continental drift.  But today, scientists know that the Earth's lithosphere is broken into massive tectonic plates that float on the asthenosphere, and are always moving and interacting.  This is called the theory of plate tectonics.  

So then what is causing the tectonic plates to move?  Convection currents in the Earth's mantle.  As a result of the uneven heating of the Earth's plastic mantle (asthenosphere), hotter, less dense mantle is continually rising, and cooler, more dense mantle is continually sinking.  This transfer (and cycling) of heated material is called convection.   Convection can occur in any gas or liquid where there is uneven heating. 

The Earth is Forever Changing
The constant movement changes the Earth's surface, rearranging and reshaping its landmasses, creating mountains, new sea floor, volcanoes, Earthquakes, and land rifts.  In fact, the continents are still moving.  North America and Europe are moving away from each other at the rate of about 2.5 centimeters per year.  In another 360 million years, it is even possible that another super-continent may form someday!

Earth's Interior Structure
The Earth is made up of four layers:

• Crust: Solid, outer layer of the Earth (5-40 km)
• Mantle: Molten rock beneath the crust (~2900 km)
• Outer Core: Molten iron layer beneath the mantle (~2250 km)
• Inner Core: Solid iron layer beneath the outer core (~1200 km)

The lithosphere is made up of the crust and the upper most part of the mantle.  Beneath the lithosphere is the melted part of the mantle is called the asthenosphere.  The asthenosphere is not quite liquid or solid.  The asthenosphere is thick and gooey, much like lava.  In fact, lava is the molten rock that erupts from volcanoes, but is called magma when beneath the surface (crust) of the Earth.  Scientists often refer to this thick and gooey texture as plastic, which describes things that are easily shaped or molded.  In case you didn't know, molten = melted (think: molten chocolate cake). 

Why do you think the density (how tightly packed the particles of a substance), pressure, and temperature all increase as you go deeper into the Earth?  On the right is a picture that may help you make an inference before we learn more about the properties of matter in the upcoming weeks.  Who do you think is feeling the most pressure?  Who do you think is feeling the least pressure?  Who do you think is feeling the warmest?  Who is the most squashed?!

The Different Physical Properties of Earth's Layers
The video below further divides the Earth's four layers (crust, mantle, outer core, inner core) according to their physical properties.  If you have ever wondered if it is possible for someone to dig to the center of the Earth, you'll find the answer below, too!

Model of Earth's Interior
Every year, Ms. Shon's students build scale models of Earth's interior.  Keep in mind that In order to do this, students must understand both the interior structure of Earth, and how to convert units.  Are you ready to design and build a scale model of Earth's interior?  (interior = inside) I hope so!

Scientists have organized the Earth’s 4,600 million year history (=4.6 billion history) into a massive timeline called the Geologic Time Scale (GTS).  The Geologic Time Scale is divided into huge time intervals that are further sub-divided into smaller time intervals.

Scientists have divided this timeline into huge “chunks”, or intervals, of time.  The largest "chunk" of time is known as the Supereon.  Supereons are broken down into smaller units of time called Eons. Eons are further divided into Eras, and Eras are divided into periods.  The “chunks” are all divided by huge events that end one and begin another.  

Since the Earth is so old, scientists describe most events in terms of “Million Years Ago” (MYA).

MYA = million years ago
1.  Cenozoic Era (65 MYA to present)
2.  Mesozoic Era (250-65 MYA)
3.  Paleozoic Era (544-250 MYA)
4.  Precambrian Eon (4600-544 MYA)

The Precambrian Supereon makes up the first 4 billion years of our planet’s history, which is almost 90% of the earth’s entire history!  The Precambrian Supereon began with the birth of the earth, and ended with an event called the “Cambrian Explosion”.  During the Precambrian Supereon, the atmosphere and oceans formed, and marine life originated.   We know this from fossils that date over 60 million years old. Some fossils include worms, jellyfish, corals, and other primitive invertebrates.

The Paleozoic Era began with the “Cambrian Explosion”, which was about 544 million years ago.  The “Cambrian Explosion” introduced a diversity of new marine life forms, as well as life forms on land.  The Paleozoic Era ended with the greatest extinction on earth caused by the impact of an asteroid 250 MYA.  

The end of the Paleozoic era brought on the beginning of the Mesozoic era, which was the era of dinosaurs and the first mammals!  During this time, the super-continent “Pangea” also began to break up.  The Mesozoic Era ended when a meteor hit the earth 65 MYA, killing many life forms, as well as making dinosaurs extinct. 

This event marked the beginning of the Cenozoic Era, which is the age of mammals, birds, bony fish and flowering plants. The Cenozoic Era began 65 million years ago and has not ended yet.  During this era, a number of mountain ranges were formed. Some of these were the Alps, Andes, and Himalayas. Along with mountain ranges, some volcanoes were formed. The animals and plants that we are familiar with today came in to existence during this period, including human beings.  

We humans are very new to planet earth.  The first human ancestor was on earth only 2 MYA, and the first modern human was on earth only 0.4 MYA!

Check out the following online interactive resources about the Geologic Time Scale:

• BrainPop: Geologic Time (Username: ms881, Password: ms88rocks)
• UCMP Berkeley: Understanding Geologic Time
• National Geographic: Pre-historic Timeline

Assignment
See the questions on the Google Classroom stream/wall.