Download Fall and Spring/Physical Science Title: GEOLOGY Revised 11/95

Title: GEOLOGY
Fall and Spring/Physical Science
Revised 11/95
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Program Goal: Each student will gain a deeper understanding and appreciation of their “place”,
including their community, their regional surroundings, their planet, and the universe.
Class Goals: Students will gain an appreciation and understanding of the Earth’s processes,
geologic history and dynamic nature.
Class Theme: “Every rock tells a story, and we can learn how to read those stories with the
science of geology.”
Correlation with California Science Framework Themes: Systems and Interactions, Energy,
Scale and Structure, Patterns of Change, and Evolution. Green Meadows themes: Sense of Place.
Objectives:
1. Students will recall the three main types of rock and how they are formed
2. Students will become aware of the vast nature of geologic time, and gain an approximate
knowledge of the sequence of events in the geologic history of the Sierra Nevada.
3. Students will be able to describe the origin of granite (plutonic vs. volcanic rock) and name
the four main minerals that compose granite.
4. Students will become acquainted with various geomorphic process, and will be able to name
at least 5 ways rocks can change due to these processes.
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Materials:
Samples of various igneous, metamorphic, and
sedimentary rocks
Rock hammer(s)
Goggles
Hand lenses
Mineral samples: Biotite, Hornblende, Feldspar,
Quartz
Timeline cards
Poster of Earth layers
Oreo Cookies
Erosion Boxes (set up and leave up)
Each One Teach One cards
Course Description
I.
Introduction: Know Your Rock
Supply each student with a rock from the pack. Give the students about one minute to get
familiar with their rock. Tell them that they need to get to know their rock so well that they can
identify it later. Ask them to feel the texture, to look at the color, shape. size and to think of
words to describe their rock.
Have the students give their rocks back to the instructor. Mix up the students, help them
get into a circle and then sit down with their hands behind their backs. The instructor then gives
each student a rock and calls out “pass” at about two second intervals. The students must pass the
rocks clock-wise. As soon as someone believes that they have their original rock they call out
“rock.” They check and keep it in front of them if it is theirs. Then they continue passing rocks
behind their back. The game continues until everyone has found their original rock.
A shorter version is to simply pile the rocks in the center and mix them up, then have
each student find their rock. This happens very quickly.
II.
A.
Rock cycle
Rock Cycle Role play
Tell the students that far below the surface of the earth, where this journey begins, it is
hot enough that rock is molten. This hot liquid rock underground is called magma. Your students
begin their role play as a swirling mass of magma. After they have swirled sufficiently, they get
shot out of a volcano and land on the earth’s surface. To demonstrate this, have them run from
one area to another. Once they get there, they begin to cool and slow down because they are
hardening into rock. The rock that they become, lava rock, is an igneous rock because it forms
from cooled magma. To symbolize a large mass of igneous rock, have the students clump
together connecting hands to shoulders.
You then become the forces of erosion (wind, water) and begin to erode the mass of
students. As you disconnect students from each other have them follow you, telling them that
they are now tiny pebbles flowing downstream towards the ocean.
Once you get to the “ocean” (another area) the pebbles will start to settle to the bottom.
The larger pieces will sink first and the smaller later. To simulate this, break the group up into
three or four smaller groups, line each group up shoulder to shoulder, and have them “settle out”
as a group. One group will stop settling on a line that represents the bottom of the ocean. Each
successive group will line up behind the first group. As they settle, they will compact close
together in their respective lines and will form sedimentary rock. Sedimentary rocks are formed
by the compaction of tiny pieces of pre-existing rocks.
As their rock gets compacted further this pressure coupled with the increased heat from
being buried can change the rock once again. A rock that has undergone change due to heat and
pressure is called metamorphic rock. Simulate this by compacting the students even more and
pushing in on the sides giving their lines a rippled effect.
They have just undertaken one possible trip through the rock cycle. Ask the students how
the cycle could continue. Possibilities include: the metamorphic rock could get buried further,
melt and reform into an igneous rock. The magma could cool beneath the Earth’s surface and
form granite instead of lava. The rocks on top of the metamorphic rock could erode exposing the
metamorphic rock to the forces of erosion. It is important to note that rocks change from one
type to another in many ways and this simulation is just ,one possibility.
B.
Rock Type Game
.Teach the students hand motions for each type of rock as follows:
Sedimentary = slap one hand on top of the other, alternating hands, while saying “layer after layer
after layer after layer.”
Metamorphic = slap hands together and simultaneously rub and push while saying “heat and
pressure, heat and pressure.”
Igneous = make an exploding motion with arms while saying “volcano! volcano!” The students
sit in a circle with one person as “it” standing in the center of the circle. “It” tries to catch
students off guard by choosing someone and saying one of the three rock types three times fast
(e.g., “igneous, igneous, igneous!”). The chosen student must make the correct hand motion and
statement about how that rock type is formed before “it” has finished saying the rock type the
third time. If the student fails to say the correct rock type in time, they become the new “it.”
C.
Review Original Rocks and classify
As a follow up/check for understanding, have the students take the rocks they got to know in the
first activity and have them try to classify them based on what they know. Remind them of the
possibilities: igneous rock could have formed intrusively, that is, below the surface of the
Earth, and cooled very slowly, thus allowing time for crystals to form, or it could have formed
extrusively, that is, cooled on the surface of the Earth, very quickly, with no time to form visible
crystals, but there may be gas bubbles. Sedimentary looks like the sediment it was formed from
(sandstone looks like sand, mudstone like mud, etc.) and shows layers. Metamorphic may have
layers, but they will show some crystals and be shiny, sparkly, or be wavy. Metamorphic rocks
are harder than sedimentary rocks because of the pressure.
III.
A.
Hike to stream (behind V-ball, near Miwok, or past beaver pond area)
Examine cobbles
1.
Why are they round? The creek moves and smoothes the rocks by rolling them
and knocking them against each other. Most movement occurs in large floods.
2.
Erosion: Water moves more than rocks -- lots of sediments from up hill get
washed into creek and carried downstream and deposited. All of the fertile soil of the
Central Valley came from the mountains originally. As the river carries materials, it
scours out its bed, deepening the channel and eventually the valley.
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B.
Break apart granite rock
1.
Examine fresh face: What do students notice about it? Get descriptive words, such
as speckled, shiny, rough, etc. Why is it like that? What are the speckles?
2.
Minerals in granite: there are four main types of minerals in all granitic rocks.
They are present in varying amounts and crystal sizes, creating the different types of
granitic rocks such as diorite, granite and granodiorite. The minerals can be found as sand
grains on the beach, or by examining larger rocks, especially if any freshly broken pieces
can be found. The four minerals are as follows:
a.
Biotite Mica: A flat, finely layered mineral which is black (sometimes
with a gold sheen -- it is often mistaken for “fool’s gold” in Big Creek), shiny and
has a hexagonal or round shape when viewed from the “top.” The layers can be
split apart with a fingernail if you can find isolated grains in the sand.
b.
Hornblende: Also black, but, not shiny or flat. Less dark, almost charcoal
in color, forming little oblong shapes or rectangles in the granite.
c.
Feldspar: An opaque white or pink mineral with faces that shine at certain
angles. Turn your sample in the light to see the shiny faces. Forms rhombus
(squashed square) shaped crystals.
d.
Quartz: Glassy in appearance. In granite, usually a whitish, glassy looking
pebble rather than a well-defined six-sided quartz crystal.
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C.
Hunt for same minerals in sand: See how many of the four minerals students can find
lying loose in the sand. Who can find the best specimens? You might want to keep some to add
to our collection. How did the minerals get out of the rocks and into the sand?
IV.
Play Mineral Tag
A large outdoor playing area with visible landmarks is designated: this bush is Big Creek, this
tree is Secret Meadow, this rock is Observation Mountain, this tree is White Chief Mountain.
The teacher calls out a landmark. Everyone must run to the landmark before the count of five.
Anyone who is late is now magma. The teacher next calls out the name of a crystal. The students
must get into the proper formation: Mica is two people back to back with their arms linked (flat).
Hornblendes three people together like a train (small rectangle). Feldspar is four people holding
hands in a square. Quartz is six people, in a circle, with their hands all together above their
heads. If anyone is left over they become magma. Now when the teacher calls out a formation,
the magma students must try to tag them before they reach their landmark. The magma students
must run with linked arms, “blob tag” style. Anyone who is tagged by the magma is also magma.
V.
Hike to Lava Rock outcrop (up Star Lakes Road, to Secret Meadow, or past it on road,
or up horse trail past Eagle Rock)
A. Examine Lava rocks/compare to granite. This rock is different than the granite we found in
the creek. What is different about it? What kind of rock do you think it is? Did it cool fast or
slow? Notice the bubbles -- these were from escaping volcanic gasses. The lava cooled so
quickly that the bubbles are frozen in place.
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B. Where are the volcanoes? We’re standing on them! This lava flow is the most recent in
Yosemite’s history “only” about 3 million years old. The ancestral Sierra Nevada was a range of
volcanoes, much like today’s Cascades. The lava from those ancient mountains has all eroded
away, leaving only the granite that was 6 miles below the surface as a magma chamber. Guess
where the eroded lava ended up? The Central Valley. There are thousands of feet of sediments in
the Valley, and they are all from these mountains.
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VI.
Geologic history of area
A. Timeline Activity: Human Timeline:
Pace off a 45-step line -- each step represents 100 million years of the Earth’s lifetime (4.5
billion years old / 45-steps equals 100,000,000 years a step). Then distribute event cards, one to a
student (some can be left out if there aren’t enough students).
Event Cards (Event only and no date are written on the cards):
1.
Beginning of the Earth - 4.1 billion years ago (Early Precambrian)
2.
Unicellular life - 3.4 billion years ago (Middle Precambrian)
3.
Multicellular life - 700 million years ago (Cambrian)
4.
Bone bearing animals - 500 million years ago (Silurian)
5.
Fish are the major life form - 400 million years ago (Devonian)
6.
Dinosaurs appear on earth - 225 million years ago (Triassic)
7.
First birds appear on earth - 175 million years ago (Jurassic)
8.
Flowering plants appear - 150 million years ago (Cretaceous)
9.
Dinosaurs die out (become extinct) - 65 million years ago (Cretaceous)
10.
Sierra Nevada begins uplifting -- 25 million years ago (Tertiary)
11.
Horses, apes, dogs, and cats appear - 10 million years ago ( Tertiary)
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12.
Hominids ( human ancestors) - 3.5 million years ago (Quaternary)
13.
Human appear on earth - 100 thousand years ago ( Quaternary)
14.
Last glaciers retreat from Yosemite - 10 thousand years ago (Quaternary)
15.
Yosemite National Park created by an act of Congress - 100 years ago.
Ask students to line themselves up on the 45-step line in the order that the events on the cards
happened, and also spaced from the start (beginning of the Earth) at what they think are the
correct time intervals. When this is done, you’ll usually get close to the correct order, but they’ll
be equally spaced along the line. Now you come along and remind them that each step is
100,000,000 years of the Earth’s history, and position them ( or let them position themselves) as
you read off the dates and distances.
1.
4.5 billion years ago -- Start of the line
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2.
Two billion years ago -- 20 feet from the end of the line
3.
600 million years ago -- 6 feet from the end of the line
4.
500 million years ago – 5 feet from the end of the line
5.
400 million years ago -- 4 feet from the end of the line
6
300 million years ago -- 3 feet from the end of the line
7.
200 million years ago -- 2 feet from the end of the line
8.
100 million years ago -- 1 foot from the end of the line
9.
80 million years ago -- 9 inches from the end of the line
10..
10 million years ago -- 1 and 1/4 inches from the end of the line
11.
8 million years ago -- 1 inch from the end of the line
12.
2 million years ago -- 1/2 inch from the end of the line
13.
10,000 years ago -- hair’s width from the end of the line
14.
100 years ago -- 1/100 hair’s width from the end of the line
Why is everybody so crowded at the end? Humans haven’t been around too long, have we?
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B. Sierra Nevada Timeline: Now fit in the dates of events in the geologic history of the Sierra
Nevada to the timeline.
500-220 million years ago: Deposition and formation of sedimentary rocks under water on the
sea floor adjacent to the western North American continent.
220-80 million years ago: Subduction of a tectonic plate to the west causes uplift and folding of
the sedimentary rocks into an “Ancestral Sierra Nevada” volcanic mountain range and
emplacement of granite underneath. El Capitan granite cools and crystallizes 108 million years
ago, Half Dome granodiorite cools and crystallizes 87 million years ago.
80-25 million years ago: Erosion reduces ancestral Sierra Nevada to rolling upland with low
relief, granite core is being exposed.
25-10 million years ago: Uplift and tilting of Sierra Nevada batholith. As stream gradient
increases, canyon cutting produces current Sierra Nevada with high relief.
20-3 million years ago: Volcanic activity is renewed in the Sierra Nevada north of Yosemite
with lava flows, volcanic tuff, and volcanic mudflows. Local eruptive events in the southern
Sierra continue to create small lava flows and basalt plugs such as seen at “Little Devil’s
Postpile,” formed 9 million years ago. The most recent igneous activity in Yosemite was about
3.5 million years ago near Fish Camp!
10-2 million years ago: A significant uplift of Sierra Nevada. Onset of San Andreas Fault.
Rivers continue to cut and deepen V-shaped valleys.
2.5 million to 20 thousand years ago: “Ice Ages” of several major glacial periods. Canyons
widened to steep, U-shaped valleys.
700 thousand to 600 years ago: Volcanic activity on the east side of the Sierra produces the
Long Valley Caldera, Mammoth Mountain, Inyo Craters, Devil’s Postpile, and the newest
mountain range, the Mono Craters.
10 thousand years ago: Ancient Lake Yosemite is formed by meltwater from glaciers filling up
Yosemite Valley, dammed by moraines. Streams from the receding ice dump sediment into the
lake, building deltas and slowly filling it up. Most of the rocks of the “Ancestral Sierra Nevada”
have by now been worn down and washed away. The few remaining examples are referred to as
“roof pendants.”
4 thousand years ago: First humans (Native Americans) enter the Yosemite Area.
150 years ago: First Europeans “discover” Yosemite
130 years ago (1865): Josiah Whitney theorizes the formation of Yosemite Valley by “the
bottom dropping out’ via earthquakes. John Muir argues that “the bottom never dropped out of
anything the good Lord made,” and theorizes that the Valley was formed by glaciers. Whitney
calls him an “ignoramus” and a “mere sheepherder.”
115 years ago (1879): Galen Clark dynamites El Capitan moraine, draining Yosemite Valley’s
wet meadows.
83 years ago (1913): There are now 12 different theories explaining Yosemite Valley’s origin.
65 years ago (1930): Francois Matthes, after much mapping and studying, comes out in favor of
John Muir’s glaciation theory of the formation of Yosemite Valley.
Present: continuing uplift on eastern boundary of Sierra Nevada causing occasional earthquakes.
The mountains are getting higher faster than they are wearing down, so the range is still growing
about 1 ½ inches every 100 years.
VII. Is Geology still going on today?
A.
Geologic forces:
1. Earthquakes/plate tectonics -- Mountains still rising
a. Journey to the Center of the Earth Activity: Show poster of Earth’s cross
section (or draw on dry erase board, like a pizza slice -- anyone like pizza?) Get
into a slice of the Earth and label the parts:
i. Crust = 2 - 25 miles deep. Volcanoes, even the magma chambers, are all
in the crust, and do NOT go all the way to the center. The crust includes
part of the lithosphere, which is made up of moving rock plates, the
tectonic plates.
ii. Mantle = 1800 miles deep. The upper mantle includes the lower part of
the lithosphere and the asthenosphere, which is made of rocks not as
strong and stiff as the lithosphere, semi-fluid or plastic in nature.
iii. Core = 2160 miles deep. Made up of the outer core, which may be
liquid -- molten nickel and iron, and the inner core, which is thought to be
solid, extremely dense iron and nickel.
Have the students act out the layers in their “slice” of Earth pizza like so:
1 student = Inner Core, flexes muscles and says “dense, solid iron”
2 students = Outer Core, say “hot, dense, plastic, material”
3 students = Deep Mantle, say “Hot rocks! Hot rocks!”
4 students = Asthenosphere, say “liquid, moving, molten material”
5 students = Lithosphere, imagine carrying full plates of pizza overhead
and shout “Moving plates! Moving plates!”
Debrief with a discussion of what plate tectonics means to us today. [Earthquakes,
mountains still rising, volcanoes, hot springs, minerals like gold and silver that are
deposited geothermally, iron ore deposits for metal]
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b. Oreo geology (plate tectonics experiment): Pass out Oreo Cookies and show
students how to demonstrate plate tectonics with them: separate the halves, then
have the half with the cream filling get “subducted” beneath the other half,
scraping all the filling into a pile. That’s kind of like mountain building! Snack
time!
c. “Push Up” model of Sierra: Demonstrate that the Sierras are tilting by having
one student get into push-up position. Lowered position is like the Sierra after the
Ancestral Sierra Nevada eroded down to low rolling hills. Then the movement of
the plates changed below the range and uplift was renewed (do a push up). The
east face (where the person’s face is) is very steep, but the western slope, the side
we are on, is more gentle As the slope increased (sot steeper), the rivers flowed
faster and had more erosive power to cut deeper valleys.
2. Erosion -- rivers still cutting canyons, carrying sediment and depositing it
a. Stream tables/erosion boxes experiment: Shallow boxes with sand in them
serve as demonstrations for the erosive power of water. Try different angles to see
the different patterns water makes in the sand. See if you can create alluvial fans,
steep canyons, or meandering streams.
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3. Weathering of rocks: rocks weather and erode into smaller and smaller pieces,
becoming sand and eventually fine silt in the soil. Granite “decomposes” via mechanical
and chemical weathering into its separate mineral grains which we call sand. There are
some good examples of decomposing granite on this trail and the same mineral grains
seen in the granite rocks can also be seen as grains of sand on the trail.
a. Chemical weathering: The mineral structure of the crystals in granite is
affected.
i. When water comes into contact with the finely layered biotite mica
crystals, it gets between the crystals, causing them to expand and break
apart the matrix of the rock.
ii. Feldspar is chemically changed into clay upon exposure to rainwater
for great periods of time, which removes it from the rock matrix,
loosening the other mineral grains present.
b. Mechanical weathering: Physical forces act on the rock, breaking the rock into
smaller pieces. Examples of mechanical weathering are
i. Earthquakes and breakage by other rocks hitting them in rock slides,
ii. tree roots breaking them, or other plants such as the lichens breaking
them down slowly with weak plant acids,
iii. rounding by rivers and streams (the actual rounding is not from the
water, but from the movement and bumping and rolling for years and
years),
iv. and ice wedging. This occurs when water gets into tiny cracks or joints
in the rock and freezes. Water expands when it freezes and acts as a
wedge, making the cracks larger. Years of this will ultimately result in
pieces of rock, from small to enormous, being broken off.
4. Examine the Lichen on the boulders.
a. Lichen grows very slowly, some species only grow a few millimeters per
century! So some of the patches of lichen may be hundreds, even thousands of
years old, if they are very large. Lichen is therefore used by geologists to date
glacial episodes and rock slides, and even old stone monuments like those on
Easter Island.
b. Lichen can also be used to determine air quality, as it is sensitive to pollution.
c. There are three main forms of lichen:
i. Crustose, mostly on the rocks -- very flat (crust-like), pale bluish-green,
olive green, bright orange, and yellow;
ii. Foliose, leafy, like the paler green variety that often grows on the
branches of trees and sometimes grows on rocks, with “leaves” that are
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cup-like and olive green on the inside, and
iii. Fruticose. highly branched, like the chartreuse green variety on the
trunks of the trees that indicates the snow level.
d The lichen story: “Alice Algae and Freddy Fungus took a lichen (liking) to
each other! Their relationship is often on the rocks, but they will also go out on a
limb for each other. It’s a very traditional relationship, because Alice does the
cooking (she’s got chlorophyll, so she makes food with sunlight, CO. and water
by photosynthesis) and Freddy built the house so Alice could move away from the
water where she normally lives. Freddy is a real Fungi (fun guy), but Alice’s
parents aren’t happy, because she and Freddy are living in sym(biosis),”
e. Symbiosis. Lichen is not just one organism, but two organisms living together
in mutual symbiosis. Mutual symbiosis means that both organisms benefit from
the relationship. Ask the students how the algae and the fungus parts of the lichen
benefit from their relationship.
B. Rock to Rock (rock cycle review)
Imagine that you are a rock as big as a baseball. Your home is on a sunny hillside
and you can see down into a deep valley with a river roaring far below. You like your
home. Sometimes it is very hot there. Can you feel the sunlight warming you?
During winter you get worried about the ice that freezes in the crack on top of
you. This crack grows bigger each year because the ice pushes hard on the sides of the
crack.
One spring it is very wet, wetter than you can ever remember. The rain pours in
little streams rushing down the hillside. Feel the water flowing over you and into the soft
mud below.
Suddenly you feel a rumbling and the Earth begins to shake. You look uphill and
a large wall of mud rushes down and sweeps you up. You begin to roll down, down,
down into the valley. Ow! You hit another rock and you split along the crack. Now you
are two halves rolling down the hill.
Splash! You land in the river. For days and days you are pushed by the swift,
strong waters. Rolling and bumping along, you are getting all broken up into gravel and
sand. Finally, the river enters the ocean and your many pieces settle onto a large, flat area
along with millions of other pieces of sand, gravel and silt.
Some pieces settle on top of you and you are getting squashed. You yell out,
“Stop pushing!” but more and more weight presses down. Your pieces get pushed and
stuck together with other pieces. You are now hardening and becoming a sedimentary
rock.
The pressure grows and you begin to get warmer and warmer. You change color
and form into many hard crystals. Now you’re a metamorphic rock.
You keep getting pushed farther down. It is hot. It is boiling hot! Everything
begins to melt and you are part of a hot mass of melted rock called magma deep
underground. It seems like forever that you are part of this big melted sea of rock. Will
you ever see the sun again? You want to be back on your hillside feeling the warm sun
and the cool wind and rain.
Wait, you’re being pushed up and the Earth is shaking and rumbling again. You
can feel yourself rising higher and higher. Fire, ash, dust and steam surround you and,
with a loud explosion, you burst up out of the top of a volcano. Red-hot lava is all
around. You are a scalding, steamy piece of lava shooting through the air when,
suddenly, you land on a high point of the volcano away from the hot flow of lava below.
Slowly, the volcano begins to quiet down and the lava cools and hardens. You are
now a cold, grey igneous rock on top of a high volcano looking down at a river flowing
far below. When the dark ashes blow away and the sky clears, the sun comes out and
warms you high up on the volcano -- your new home.
[From Keepers of the Earth, p. 61]
VIII. Each One Teach One as review on hike back
Find a comfortable spot for your group to hang out. each student needs to be assigned a
number. The numbers will match up to the number on the hike cards. there are 17 hike cards
(number 18 is for the instructor) so you will need to pair up some of the students if you have
more than 17, or you will need to give some students two hike cards if you have less than 17. Do
not give out the hike cards ahead of time.
The instructor hikes down the trail about 50 feet with the number 1 student. the student
receives the first hike card with information about tectonic plates. The instructor needs to model
for the student how to teach the information. It is that student’s duty to teach all other students
about tectonic plate action. The student will stay in that spot until the cabin leader comes to her
station to pick her up.
The instructor moves up the trail about 35 feet, (farther if it is a path that is well known to
your students) and waits for the next student. Meanwhile, the cabin leader sends the next student
on the trail. He/She will send one student, or pair of students, every 2 ½ minutes. The instructor
continues to hand out the cards to the students every 35 feet (or more) along the trail. The
instructor will wait at the end with card number 18.
The cabin leader will be the last one down the trail. He/She will pick up the students at
each station. The group will grow ever larger. Finally, student number 17 will teach the entire
group about Hornblende. The entire class hikes to the last station where the instructor will
conduct a review.
This can also be done without cards, just verbally give a mini-lesson to the student who
will be teaching. make sure to keep the messages really simple, only review of what has already
been learned. Give them an action, or an object to look at, or question for the other students.
Break the messages up into smaller parts so they will be remembered, if necessary. This is
sometimes called a Professor hike, or a waterfall walk.