The Earth Rocks
Exploration Phase
Topic: Rock Types – Igneous, Sedimentary, and Metamorphic
Activity I:
Rock Identification Using Rock Kits
1. Using the rock kits provided determine which rocks samples are igneous, sedimentary
and metamorphic.
2. Use the nail and magnifying lens to help you test the properties of each rock.
3. Place each rock you have identified on the appropriate corresponding sheet of paper
labeled Igneous, Sedimentary or Metamorphic Rock.
4. Leave any rock samples you were not able to classify in the rock kit box.
Activity II:
Peer Review
1. Share your findings and review another group’s results from the initial rock
identification.
2. Make suggestions as to which rocks may have been identified incorrectly and discuss the
rock classifications amongst yourselves.
3. As we discuss the rock samples in class, note which rocks you identified correctly and
which were incorrect.
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Content Review:
Igneous Rocks
Igneous rocks – rocks that form when molten rock (rock liquefied by intense heat and pressure)
cools to a solid state
- when molten rock cools, it always forms a mass of intergrown crystals and/or
glass; therefore, all igneous rocks have a crystalline or glassy texture
Igneous Processes
Intrusive vs. Extrusive Igneous Rocks
Intrusive – rocks that form by the cooling of intrusions within the earth
Extrusive – igneous rocks that form at the planet’s surface; they are extruded or
violently ejected onto the surface
Bodies of Igneous Rocks
Batholith – massive igneous intrusions (covering regions of 100 km2)
Sill – sheet-like intrusions that force their way between layers of rock
Laccolith – blister-like sills
Pipe – vertical tubes that feed volcanoes
Dike – sheet-like intrusions that cut across layers of rock (sheet dike, ring dike, radial dike)
Textures - dependent on nucleation; the atoms are mobile in a magma and free to nucleate
nucleation - initial formation of a microscopic crystals to which other atoms progressively bond
- generally if magma cools more slowly, the atoms in the magma have time to grow
- if the magma cooled quickly, the mineral crystals will be smaller because they
didn’t have time to grown and nucleate
obsidian - formed when the intense heat of a volcano fuses masses of silica together very
quickly forming the hard glass
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Examples of Igneous Rock Textures
Pegmatitic – crystals > 1cm, very slow cooling
Phaneritic – crystals 1-10mm, slow cooling
Porphyritic – large and small crystals (phenocrysts = large crystals, matrix = smaller
more numerous minerals
Aphanitic – crystals < 1 mm, rapid cooling, fluid lava
Glassy – rapid cooling
Vesicular – rapid cooling of gas charged lava, gas bubbles in lava (scoria, pumice)
Pyroclastic – particles or fragments emitted from volcanoes (tuff – volcanic ash, volcanic
breccia)
Mineral Composition
Mafic vs. Felsic Minerals
Mafic minerals (dark-colored) – ferromagnesian minerals (iron and magnesium)
Biotite Mica (black)
Amphibole (dark gray)
Pyroxene (dark green)
Olivine (green)
Felsic minerals (light-colored)
Quartz (gray)
Plagioclase feldspar (white)
Potassium Feldspar (K-spar) (pink)
Muscovite mica (brown)
Color Index (CI) – is the percentage (by volume) of mafic mineral crystals in the rock
- a rough measure of the proportions of mafic and felsic minerals
Felsic igneous rocks: 0-15% mafic minerals
Intermediate igneous rocks: 16 – 45% mafic minerals
Mafic igneous rocks: 46-85% mafic minerals
Ultramafic igneous rocks: 86-100% mafic minerals
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Sedimentary Rocks
How do sedimentary rocks form?
They form when sediments accumulate and are lithified (meaning hardened by
compression or cementation), or when masses of intergrown mineral crystals precipitate
from aqueous solutions
- Lithification of sediments
- Cementation – thin films of chemical residues “glue” grains together
- Precipitation of aqueous solutions (i.e. rock salt)
Sediments – these are loose grains and chemical residues of rock fragments,
mineral grains, animals or plants, and rust (hydrated iron oxide
residue)
- Sediments are the products of weathering processes
- All sediments have a source; either produced by biochemical (organic) processes
of
plants and animals or by chemical or physical weathering processes of
organic and inorganic materials
Physical weathering – the cracking, scratching, crushing, abrasion, or other physical
disintegration
- Large rocks will be broken down into individual clasts (broken pieces of rock fragments
and minerals)
- Plant matter, logs and animal shells will be broken down into peat and shell gravel
Chemical weathering - the chemical decomposition or dissolution of earth materials
- Feldspar and mica -- broken down into clay minerals
- Calcite -- goes to calcium and bicarbonate ions in solution
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Classification of Sedimentary Rocks
A) Clastic (a.k.a. Detrital) – rocks made up of mostly rock fragments, quartz grains, feldspar
grains, or clay minerals
B) Biochemical (a.k.a. Bioclastic) – rocks made mostly of grains that are fragments or shells
of organisms (plant/animals)
C) Chemical – made mostly of mineral crystals precipitated from aqueous solutions and/or
chemical residues (e.g. rust)
Texture of a Sedimentary Rock
- Texture is a description of its constituent parts and their sizes, shapes and
arrangements
-
Sediments can be transported great distances by wind, water and ice
-
This causes the sediment grains to be dragged, bounced, rolled, and
carried and causes grains to be scratched, broken, rounded and worn
(glacial action)
Grain Shape
Angular grains
Subangular
Subrounded
Rounded
Grain Sizes
Gravel - includes grains larger than 2 mm in diameter (granules, pebbles, cobbles,
boulders)
Sand - all grains are visible and feel gritty between your fingers (1/16mm-2mm in
diameter)
Silt - grains usually too small to see (grains from 1/256mm to 1/16mm in diameter)
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- You can feel them as tiny grits between your fingers or teeth
Clay - grains too small to see w/out microscope (grains less than 1/256mm in diameter)
- Feels smooth when rubbed between your fingers
Sorting of Sediments (Grain Arrangements) – wind and water currents transport and naturally
separate sediments into different grains sizes and densities
Well– sorted – composed of sediments that are of similar sizes; usually well-rounded
Poorly– sorted – many different sizes and/or densities of sediment grains mixed together
Metamorphic Rocks
Metamorphic Rocks – rocks that are changed from one form to another by intense heat and
pressure or by the action of watery hot fluids inside of the earth
- Examples: marble, quartzite, slate, phyllite, schist, gneiss,
metaconglomerate, anthracitic coal, etc.
Parent Rock – the original rock that was metamorphosed into a new rock; also known as
protolith; can be any of the three types of rocks (igneous, sedimentary or
metamorphic)
- Examples: limestone, sandstone, shale, conglomerate, mafic or ultramafic igneous
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Common Metamorphic Rock forming Minerals:
Quartz, Calcite, Dolomite, Feldspars, Muscovite, Biotite, Chlorite, Garnet,
Tourmaline, Serpentine, Talc, Kyanite, Sillimanite, Amphibole (Hornblende)
Contact metamorphism – occurs locally, adjacent to igneous intrusions and along fractures that
are in contact with watery hot fluids (hydrothermal metamorphism)
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- Hydrothermal Metamorphism – involves the condensation of gases
to form liquids which can precipitate mineral crystals along
fractures
- Zones of contact metamorphism are narrow from millimeters to tens
of meters thick
- Caused by conditions of moderate pressure and heating for days to
thousands of years
Regional metamorphism – occurs over very large areas (regions), such as deep within the cores
of rising mountain ranges, and is generally accompanied by folding
and shearing of rock layers
- Caused by 1) large igneous intrusions that form and cool over long
periods, 2) extreme pressure and heat, and/or 3) widespread
migration of hot fluids
* Note: most major intrusions are preceded by contact metamorphism
and then followed by regional metamorphism
Recrystallization – a process where small crystals of one mineral will slowly convert to fewer,
larger crystals of the same mineral, without melting the rock
Metamorphic Rock Textures
1) Foliated: rocks with a layered appearance
Slaty rock cleavage – very flat foliation developed along closely spaced shear planes
(slate)
Phyllite texture – wavy to wrinkled foliation of cryptocrystalline platy minerals (phyllite)
Schistosity – a scaly, glittery layering of visible platy minerals (medium-tocoarse-grained), and/or linear alignment of long prismatic crystals (schist,
garnet schist)
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Gneissic banding – alternating layers of light and dark medium-to-coarse-grained
minerals
(gneiss)
2) Non-Foliated: no obvious layering present
Crystalline texture – aggregate of intergrown crystals, medium-to-coarse grained
(marble)
Microcrystalline texture – very fined-grained aggregate of intergrown crystals (hornfels)
Sandy texture – medium-to-coarse-grained aggregate of fused sand-sized grains
(quartzite)
Glassy texture – no visible grains (anthracite coal)
3) Other Metamorphic Features
Stretched or sheared grains – deformed pebbles, fossils, or mineral crystals that have
been
stretched out (i.e. metaconglomerate)
Porphyroblastic texture – large crystals set in a finer-grained groundmass
Hydrothermal veins – fractures healed by minerals that precipitated from hydrothermal
fluids
Folds – bends and buckles in rock layers that were originally flat
Lineations – lines on rock at the edges of foliation, shear planes, etc.
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Application Phase
Activity:
1. Pass around and discuss the rock hand samples (larger classroom samples) and determine
what minerals comprise each rock.
2. Classify the hand samples by type (igneous, sedimentary or metamorphic).
Terms: Parent rock, igneous, metamorphic, sedimentary, batholiths, intrusion, mafic, felsic,
pyroclastics, lithifaction, foliation, color index, sedimentation, weathering, metamorphosis,
extrusion, layering, pressure, heat, texture.
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Teacher Notes: Additional Classroom Learning Activities
Magma Lab Activity
Objectives
When you have completed this lab you should be able to:
1. explain why magma rises through the lithosphere, often making it to the surface and out of a
volcano.
2. describe the process of crystallization and how the rate of cooling of a melt affects the sizes
of the crystals formed.
Activity #1: Why Does Magma Rise?
Materials: covered test tube of salol (phenyl salicylate)
plastic beaker of hot tap water (get from front sink)
hot plate
large glass beaker with a little boiling water in it
thermometer
insulated gloves
test tube rack
empty test tube
crushed ice
Activity
1. Melt almost all of the salol: Measure the temperature of the hot tap water. If it is below
120°, pour some out and add a little boiling water. Hold the test tube of salol in the hot water,
swirling it around gently. Periodically remove the test tube from the hot water and see if the
salol has melted. Continue this process until the crystals are almost all melted (leave a piece
of crystalline salol, about 1/8 inch across, in the melt to act as a seed crystal). This process is
analogous to the melting of rock deep within Earth’s crust or mantle.
2. Place the test tube of salol in an upright position in the metal test tube rack.
3. Fill the unsealed empty test tube about 1/3 full of tap water. Place a few pieces of crushed ice
into the water (if the ice melts, just add a little more ice).
Questions:
1. Draw two diagrams, one showing the seed crystal inside the test tube of melted salol and one
showing the crushed ice inside the test tube of water.
Test tube with a few crystals
of salol in molten salol
Test tube with a few pieces
of crushed ice in water
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2. Which has a higher density, crystalline (solid) salol or molten (liquid) salol? How do you
know?
3. Which has a higher density, water or ice? How do you know?
4. When rock melts, deep under ground, it typically isn't any hotter than the unmelted rocks
around it; it merely has a lower melting temperature than the rocks around it. Yet, the melt
(magma) tends to rise, often making it all the way to the surface as a lava flow. Why does
magma begin to rise, even though it's no hotter than the unmelted rocks around it?
Activity #2: Melting and Crystallization
Materials: 2 Petri dishes, containing salol (phenyl salicylate)
hot plate
insulated gloves
1 metal bowl with ice on the bottom (get ice from front lab table)
10x magnification hand lenses
large example of radiating clumps of crystals (in a box)
large example of a single crystal (in a box)
Make a Prediction: In this activity, you will be melting and then cooling (and therefore
crystallizing) molten salol at two different speeds. The possible results are as follows:
a. The salol whose temperature drops faster will form larger crystals.
b. The salol whose temperature drops more slowly will form larger crystals.
c. The rate of cooling will not make any difference; the crystals will be the same size, no
matter how quickly the temperature of the salol drops.
Choose the result that you think will occur. Explain the reasoning behind your answer.
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Activity
1. Melt the salol: Set the hot plate on low. CAREFULLY—supporting the bottom of the Petri
dish so that it doesn't fall, place the Petri dish on the hot plate with one side hanging 1/4 inch
or so over the edge. Let all the salol melt except for a small amount at the overhanging edge.
2. Remove the salol from the hot plate: Wearing the insulated gloves, CAREFULLY—
supporting the bottom of the Petri dish so that it doesn't fall—remove each Petri dish from
the hot plate and place it on the lab table.
2. Simulate the formation of a volcanic rock: Place one of the Petri dishes on hte bowl of
ice, causing it to cool rapidly. This rapid cooling process is analogous to the formation of a
volcanic rock; the melted rock (lava) cools and crystallizes quickly because it erupts onto the
Earth's surface, which is much cooler than the depths of the Earth. Look at the crystals with
a hand lens; note the sizes of the crystals.
3. Simulate the formation of a plutonic rock: Meanwhile, back at the lab table, the
remaining Petri dish has been cooling slowly. This slow cooling process is analogous to the
formation of a plutonic rock; the melt cools and crystallizes slowly because it stays deep
underground and has a thick insulating layer of rock above it. Look at the crystals with a
hand lens; note the sizes of the crystals.
Questions:
1. Which procedure produces larger crystals, a rapid temperature drop or a gradual temperature
drop? Why?
Hint: Be sure to base your answer on the sizes of individual crystals; not on clumps of small
radiating fibrous crystals (see the large example of similar clumps of crystals). Large
individual crystals of salol are diamond shaped if they are free to grow without bumping into
other crystals (see the large example of a similar crystal).
2. Draw enlarged sketches of some of the crystals in each test tube.
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Crystals that formed when the
salol cooled quickly
Crystals that formed when the
salol cooled slowly
3. Which should have larger crystals, volcanic rock or plutonic rock? Explain the reasoning
behind your answer.
4. What would happen if the melt were chilled so suddenly that the crystals had no time to
form? Why?
5. In terms of crystal size, what would happen if the liquid salol cooled slowly for awhile and
then was cooled quickly (placed in ice water)? Explain the reasoning behind your answer. If
there's time, try it!
5. If magma cools slowly deep underground for awhile and is then expelled quickly onto the
surface, will the crystals be big or small? Explain the reasoning behind your answer.
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Activity #3: Watching the Crystallization Process
Materials: glass Petri dish full of salol (phenyl salicylate), with glass cover.
hot plate
10x magnification hand lenses
insulated gloves
paper towels
Activity
1. Melt the salol: Set the hot plate on low. CAREFULLY, supporting the bottom of the Petri
dish so that it doesn't fall, place the Petri dish on the hot plate with one side hanging 1/4 inch
or so over the edge. Let all of the salol melt except for a small amount at the overhanging
edge.
2. Remove the salol from the hot plate: Wearing the insulated gloves, CAREFULLY—
supporting the bottom of the Petri dish so that it doesn't fall—remove the Petri dish from the
hot plate and place it on the lab table. If the cover glass fogs up (usually it does), briefly
place the cover glass upside down on the hot plate; then wipe the inside with a paper towel
and put it back on the Petri dish.
3. Watch the salol crystallize again: Using the magnifying hand lens, watch the crystals form
and grow.
Questions:
1. Do crystals start growing all over the dish or do they start in a few spots and grow bigger
from there? Describe what happened.
2. Try repeating the experiment but place the dish on a bed of ice. This time, do the crystals
start growing all over the dish or do they start from a few spots and grow bigger from there?
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Sedimentary Processes Lab
Objectives
When you have completed this lab activity, you should be able to:
1. explain the essential difference between chemical sediment and detrital sediment.
2. describe how and why detrital sediment is deposited.
3. describe how and why chemical sediment are deposited.
4. explain how the speed of flowing water affects (a) the sizes of detrital sediment particles
that the water can carry and (2) the sizes of detrital sediment particles that the water
deposits.
5. explain why detrital sediment is often layered by particle size.
6. distinguish two very different mechanisms by which crystals can grow in a fluid.
7. explain how sediment is transported from far inland to the sea.
8. describe how running water can transform a featureless terrain into a complex landscape of
ridges and valleys.
9. distinguish between erosion and deposition.
10. identify the following features of a river: tributaries, trunk stream, delta, distributaries
Important Definitions
Dissolved: a substance is dissolved in a fluid (liquid or gas) when its component ions, atoms or
molecules have become separated and individually surrounded by molecules of the fluid.
Sediment: solid material that has settled to the ground or to the bottom of a body of water.
Chemical Sediment: Sediment that was once dissolved in water.
Detrital Sediment: Sediment that was never dissolved in water.
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Activity #1: Chemical vs. Detrital Sediment
Materials: 1 clear plastic cup containing fine-grained halite (table salt)
1 clear plastic cup containing powdered clay
water
2 stirring rods
Prediction: Which do you think will dissolve in water: the salt, the clay, neither or both? Explain
the reasoning behind your answer.
Activity: • Add water to each cup until it is approximately 2/3 full.
• Thoroughly stir the contents of each cup for at least a minute.
• Observe each cup right after you have finished stirring.
Questions:
1. Draw diagrams of the two cups immediately after you have finished stirring.
Water + Salt
Water + Clay
2. Which substance dissolved in the water: the clay, the salt, neither or both? Use your
observations of the two cups to justify your answer.
More Activity: • Let the two cups rest undisturbed on the lab table for an hour or so.
More Questions:
3. Draw diagrams of the two cups after they have rested on the lab table for an hour or so.
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Water + Salt
Water + Clay
4. Explain why the distribution of sediment in the two cups is so different.
5. Clay is a
Salt is a
detrital
detrital
/
/
chemical
chemical
sediment (circle the correct answer).
sediment (circle the correct answer).
Activity #2: Causing the Precipitation of Chemical Sediment from a Solution
Materials: salt water (solution of sodium chloride in water)
spoon
one glass Petri dish
10x magnification hand lenses
metal stand with a heat lamp on it, pointing down
Activity
1. Place a few spoonfuls of salt water into the Petri dish. Look at the solution with a hand lens. Draw a diagram of the Petri dish in the
space provided below (Question 1).
2. Place the Petri dish under the heat lamp and let the water gradually evaporate. Go on and
do Activities 3 and 4. After 10-15 minutes, examine the Petri dish and answer the questions
below.
Questions:
1. Draw diagrams of the Petri dish, before and after the water evaporated.
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







Before Water Evaporated
After Water Evaporated
2. What caused the crystals to form in the Petri dish?
3. How is the process that formed these crystals fundamentally different from the process
that formed the crystals of salol in the test tubes (you did this a couple of weeks ago)?
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Activity #3: Studying the Deposition of Detrital Sediment
Materials: Mason jar with water and detrital sediment in it.
Dry detrital sediment: Mixture of gray pea gravel, fine white sand and a small amount of
dark silt (the black "dirt" in central and western Chico is ideal).
Activity:
1. Shake the jar vigorously; the water picks up the detrital sediment, just as a flowing stream
does.
2. Stop shaking the jar and watch what happens to the detrital sediment as the water slows down
and comes to rest.
Questions:
1. What causes the detrital sediment to become suspended in the water?
2. What causes the detrital sediment to settle to the bottom of the jar?
3. Do the smallest grains land on the top or on the bottom of the layer? Why?
4. What is the important factor in determining which grains land on the bottom of the layer,
their weight or their density? Why?
(Hint: what happens to the density of a large boulder when it's broken into small pieces?)
5. What natural river or ocean processes could result in the deposition of detrital sediment?
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6.
After most of the detrital sediment has settled, draw a diagram of the sediment in the jar,
noting especially any variations in the size and/or color of the sedimentary particles.
More Activity: Open the top of the jar and add another 1/4 cup or so of sediment; watch it settle.
Repeat several times. Note the layering; such layering is always present in
sedimentary rock.
Questions:
7. Draw a diagram of the multiple layers of detrital sediment in the jar, noting especially
any variations in size and/or color of the sediment.
8. Describe a natural scenario that could result in the deposition of distinct layers of detrital
sediment.
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Activity #4: Watching Running Water Modify a Landscape1
Materials: 2 large plastic trays, each with a small hole in one end
small rubber stopper
moistened sediment (diatomaceous earth--the kind used for swimming pool filtration- mixed with a small amount of fine sand)
flat plastic spatula
large (1 or 2 liter) plastic beaker
spray bottle full of water
sponge
Activity:
1. Initial set-up
a. The sediment in your tray should be pre-moistened. If it is not, ask your instructor to do
it.
b. Plug the hole in the tray with the rubber stopper. Mix the moistened sediment well, using
the plastic spatula and/or your hands. You will have to scrape the sediment off of the
bottom using lots of elbow grease. Mix the sediment well until the sand (tan) is evenly
distributed in the diatomaceous earth (white). If necessary, add some water until the
sediment has the consistency of a mud pie.
c. Turn the empty tray upside down. Rest the tray containing the moistened sediment on the
edge of the empty tray, with the plugged hole on the uphill side of the tray.
Rubber stopper
Empty Tray
Tra y Co
ntai ning
M
oistene d
Se dim e
nt
d. Push the sediment to the side of the tray opposite the hole. The sediment should cover
about half of the bottom of the tray.
e. Firmly pat the sediment with your hands to make its upper surface as flat as possible (it
will become very soupy when you do this).
f. Use the sponge to clean as much sediment as possible from the exposed bottom of the
tray.
1This
laboratory activity was modified from
a) The River Cutters unit of the Great Explorations in Math and Science (GEMS) curriculum materials for Grades
6–9, published in 1989 by the Lawrence Hall of Science, University of California at Berkeley.
b) The Stream Tables activity of the Landforms Module of the Full Option Science System (FOSS) curriculum
materials for grades 5–6, published in 1990 by the Lawrence Hall of Science, University of California at
Berkeley; distributed by Encyclopaedia Brittanica.
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Comments: This is a small-scale model of a landscape. An inch on the model represents about a
mile on a real landscape. A grain of sand represents a boulder. Regarding evolution of the
landscape, one minute of the experiment is equivalent to about 1000 years in real life.
2.
Running the Experiment:
a. Gently and slowly (so as not to disturb the sediment), place the tray of sediment flat on
the upside-down tray.
b. Fill the plastic beaker with water and SLOWLY pour water into the sediment-free side of
the tray just until there are no more dry spots on the bottom of the tray. This water
represents the ocean; the sediment represents the land.
Shoreline
Land
Ocean
c. Watch as water drains off of the “land.” It will form several streams. At first, nothing
may appear to be happening. Be patient and keep watching. Try to be the first in your
group to see a stream appear.
d. Continue watching as the running water carves a landscape by eroding, transporting and
depositing sediment. Be sure to watch what happens in the ocean as well as what happens
on land.
Questions:
1. Where, in the model, is erosion occurring?
2. Where in the model is deposition occurring?
3. Explain the essential difference between erosion and deposition.
4. What is the predominant sediment that is eroded from the land, transported by the streams,
and deposited into the ocean? The diatomaceous earth (white) or the sand (tan)? Why?
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5. Is sediment deposited as one even layer in the ocean, or is more sediment deposited near the
shoreline? Explain why this occurs.
More Activity: Continue Running the Experiment:
a. Gently spray a fine mist of water over the land (a few “squirts” should be enough)--you
have just made it rain!
b. Watch the water run off the land. Notice how efficiently the streams channel the water
from the land to the ocean.
c. Repeat several times, causing the landscape to continue to evolve.
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