UNIT VI. GEOLOGY
This unit is designed to cover 8-10 classes, typically
offered twice a week over a month, with one double-period field trip.
AN INTRODUCTION TO GL GEOLOGY
In this unit we hope students will experience Earth as a
dynamic system, one that is always in motion, always changing. No component, in fact, of the earth's
system is static: mountains are made and erode, rivers go straight and layer
meander; plants break apart rock; and continents move slowly but inexorably
about the globe, sometimes hovering over the equator, sometimes plowing into
each other with enough force to create the tallest mountains.
The challenge for teachers is to bring those forces that are
out of view, whether beneath the surface of the Earth, in the air, or active at
the invisible molecular level. For example, where does energy come for all of
these changes on Earth? All changes, after all, require energy. The answer is
found in the radioactive decay of elements of the core, which, heated to
thousands of degrees, forces the cooler mantle segments and crust to move in
sweeping slow convection currents.
We should not take for granted that students can see or
believe easily any of this large story.
The trees, boulders, and beaches they have known in their childhood do
not move visibly. What we can hope
for is that they become accustomed to investigating the world around them as
scientists do, and will develop a thirst for understanding their geological
past as well as an ability to predict and evaluate possible futures.
Week 1A: Rocks Around Us: Your Geological
Field Trip (teachers)
Materials
study site map
plastic bags (10)
masking tape
marker
field guide to local rocks (optional)
camera (digital preferred)
newspapers meter stick or centimeter ruler
spade or soil auger
GL Journals
Preparation:
If your class cannot go outside because of cold weather or
because a heavy snow layer is covering the land and its rocks, simply proceed
to the next activity.
1. Examining the rocks at the study site
In their journals, students make a rough sketch of the rocks
on the surface of the study site, the larger the better. Sketch and briefly
describe individual rocks and rock outcrops, marking their locations on your
study site map.
They can also write descriptions of rocks on the study
site. Encourage them to consider:
¥ Is there one type of stone that is most common on your
site?
¥ Are there tops of larger rocks under the ground?
¥ Are there outcroppings or towers of stone?
¥ What colors are the rocks?
¥ What textures are
the rocks?
¥ Do the rocks seem to have been placed there by humans?
Could they have been moved there by glaciers?
¥ Are there clear boundaries around different kinds of
rocks, or are they all found together?
¥ Is there sand? clay?
* In the larger rocks, are there layers and are they tilted
at an angle?
If there are rock breaks, look for layers and sketch them
with different colors. Be careful while approaching any ledges.
While investigating the site, help the students speculate
about the how their land might be shaped. If they have a rock or sand,
challenge them to think about where they came from and what forces might have
influenced them.
2. Collecting rock and sand samples
1. Ask students to collect several samples of the dominant
rock type and a sample of other types of rocks for the class rock
collection. Ask them to look
around and notice if there is a "parent" rock from which it has
broken.
2. Place each sample in a plastic bag and label it (using
masking tape and marker) with the location where it was collected.
3. There will be an opportunity to look more closely, to
draw or photograph the rocks at close range in the next class, but some
students might want to begin this process.
4. Enter the location of the collected rock on your study
site map.
Back at the Classroom
Wash the rocks with warm soapy water, dry and return to a
bag.
Extension: Road Cuts
If your students can observe any rock cuts in the local
roadways, ask them to sketch them and write their observations. Alternatively you could take pictures
yourself and show them in class.
Ask then to observe:
Are there layers? Do the layers alternate light (ocean
calcium deposits) and dark (vegetation)?
Are there intrusions of other materials as large veins
(dikes?)
Homework reading (Russian
only): Student Textbook Section 1: The Origin of Mountains
Your Geological Field Trip (student journal)
1. Make a rough sketch of the large boulders and
outcroppings, sand or clay deposits on the surface of the study site area.
2. Sketch and
briefly describe individual rocks, using the journal table and marking their
locations on your study site map.
¥ Is there one type of stone that is most common on your
site?
¥ Are there tops of larger rocks that have parts
underground?
¥ Are there outcroppings or towers of stone?
¥ What colors and textures are the rocks?
¥ Do the rocks seem to have been placed there by humans?
Could they have been moved there?
¥ Are there clear boundaries around different kinds of
rocks, or are they all found together?
¥ What size are many of the particles? Is there sand? Clay?
3. Collect at least ten samples of the dominant rock
type in the study site area, and a few samples of other types of rocks of rock
for the class rock collection.
4. Place each sample in a plastic bag and label it (using
masking tape and marker) with the location where it was collected.
5. Enter the location of the collected rock on your study
site map.
Back at the Classroom
Wash the rocks with warm soapy water, dry and return to a
bag.
Homework:
(Russian only) Student Text Geology 1.The Origin of Mountains
My Field Observations (journal)
My Rock Collection
Student Name:
Date:
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ROCK
NUMBER
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Where was it found?
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Color
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Texture
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Shape
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What was near it?
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Any unusual features?
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Rock # 1
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Rock # 2
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Rock # 3
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Rock # 4
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Rock # 5
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Rock # 6
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Rock # 7
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Rock # 8
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Rock # 9
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Rock #10
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Examples:
Color (white? white with black specks? purple)
Texture (smooth?
rough?)
Unusual features (veins of another material, big crystals)
Shape (round?
flat? sharp?)
Where did you find it? (on our study site, in a river, on a
beach)
What was near it? (a river? A woods? A beach?)
Adapted from the American Museum of Natural History
www.ology.amnh.org
Week 1B: Observing and Organizing the Rock Samples (teacher guide)
(1 – 2 hours)
Preparation
This activity builds on the trip to the geological study
site. If your class, however,
could not go outside, then there are several ways to obtain rocks for the
activity: use a school rock
collection, make your own collection, or ask each student to bring in a handful
of rocks.
Materials
Rocks from study site, so marked, and some others. If the rocks are from a school or local
collection, ideally there would be samples of igneous, metamorphic and
sedimentary, but not identified as such.
Magnifiers
Pencils
Microscopes
Digital camera, if possible
Overview
In this activity students organize their notes and
observations from the field trip and the rocks they collected, or explore the
rocks available in the classroom. They compare the rock samples, characterize
the features, and then hypothesize about the processes that might have formed
the rocks. They have not yet learned formally about geological processes, so
this is simply an opportunity for them to begin to generate geological
concepts.
Procedures
1. Ask your students to begin by organizing the notes
they took at the field site.
2. Then lay out and sort the rock collection. Students should:
¥ draw and take pictures of them, if they have not already;
¥ examine the rocks with magnifiers, and compare the rocks in size,
composition, texture and color
and
¥ place the rock samples in various categories. Encourage them to try more than one
arrangement.
3. Discuss the following:
* How are rocks the same and different?*
* What are rocks made of? (minerals, organic residue) (and,
finally)
* How do you imagine rocks are made?
Let the students develop their own ideas. Record them so that they can revisit
their early ideas later in the unit.
This discussion should pave the way for a discovery of the
different minerals that make up rocks, if the class undertakes a mineral
identification, and for an investigation of the three main processes that form
them.
4. Ask the students ÒWhat are other ways to tell rocks
apart?Ó
You might allow them to play with magnets, vinegar,
scratching tools to detect any differences.
5. GL SHARE:
a. Upload
drawings and photographs of their landscape and rock collections on the Global
Lab web site;
b. Share their rock categories with the class, and then vote
for those to share with Global Lab as well as the best drawings and
descriptions.
c. Compare their rocks to those of other classes
d. Make your own new rock or landscape collection of photos
drawn from those of others. Post your personal favorites? Write to author if
you want to know details.
Looking At Your Rock Collection (student journal)
Materials
journal
drawing supplies
magnifiers
Digital camera
Steps
1. Examine each rock carefully. If possible, draw or photograph it at close range.
2. See if you can locate any of the following special
features.
a. Crystals, and if so, how
big are they?
- Groupings of different crystals. Granite – the continental rock you are MOST likely to
find – is made of three minerals—feldspar, mica and quartz.
- Flat planes of crystal that can
be peeled off. (e.g. mica)
- Empty small geometric holes where
crystals have fallen out of rock
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Large untwisted crystals can be from volcanic rock. (ex: gabbro)
b. Veins of a contrasting
mineral that runs into or around a rock.
(Often the vein is white, as material with lots of chalk-like compounds
like calcite dissolves easily and
will pour through a rock opening. Green – antigorite.
c. Holes.
Smooth holes – can be fossil holes of early life such as
worms or shrimp
Many rough holes –might be
from gases in volcanic eruptions. This material cooled too quickly for
crystals.
d. Folds and twists. The rock has been twisted in collision.
e. Swirls – rock has been so molten it flows like syrup
before it hardens.
f. Bands – sediment
was laid down and hardened.
g. Colors
Rust stains -- from iron oxide
crystals in rock cracks.
Red, purple and yellow – also
from iron oxides
Black – from volcanoes,
igneous like basalt.
White "icing" –
maybe left over from a white layer of soft material that has worn away.
Green- iron oxides formed in
low-oxygen environment
3. Sort the rocks into 3 kinds of groupings. Make your own decisions about which
ones are the best.
4. Share your categories with the class, and then
select the best categories to share with Global Lab. Share pictures of the rock
collection with GL, along with any drawings and descriptions you can make
available.
In your annotation you can also share ideas of how to
display your rocks.
Homework: (Russian only) Student Text Geology 2.
(Rocks, Minerals and) Crystals
IC. Rocks, Minerals and Crystals
(English - student background reading –
probably unnecessary or teacher)
Rocks are composed
of minerals, the hard, stable crystals and glasses that make up the Earth are
called minerals. Most of the hard
stuff on the surface of the earth is rock.
Minerals are made up
of one or more one element (one kind of atom) and can exist in a pure form,
like diamonds and gold. Most are combinations.
The rock granite, for example, is a type of rock that
includes three kinds of minerals -- quartz, feldspar, and black mica. So to
identify the minerals in a rock we usually have to do a number of tests.
Quartz, on the other hand, is a single mineral (quartz!).
In fact, there are over 3000 different types of minerals!
Amazingly, most of the EarthÕs crust (99%) is made of just ten types of
minerals (the most common being feldspar and mica).
Crystals are a form
of minerals in which the atoms have had time to assemble in an orderly way.
Large crystals are often formed underground, where they can
grow slowly, atom by atom, undisturbed. Small crystals can be formed
quickly.
Percent of EarthÕs Crust by Weight
Oxygen (O) 46.0%
Silicon (Si) 27.7%
Aluminum (Al) 8.1%
Iron (Fe) 5.0%
Calcium (Ca) 3.6%
Sodium (Na) 2.8%
Potassium (K) 2.6%
Magnesium (Mg) 2.1%
Look at the list above of the key elements of the EarthÕs
crust. Which two elements make up most of the crust?
IC. Mineral Testing (advanced
student lab/journal or linked)
How can you
identify the minerals in a piece of rock? Geologists examine a variety of
characteristics to identify minerals. You can perform several simple tests in
the classroom to identify the minerals in your rocks.
Perform the following tests, record your findings, and
compare your results against the Common Mineral Identification Chart to
identify your mineral. Record the results of all of your tests in your Global
Lab Journal.
A First Test: Color
Often you can identify a mineral by its color, though not
all have distinctive colors.
Materials
rock guide book (optional)
Procedures
1 Each teammate
should carefully observe the color of the mineral, ideally under sunlight.
2 The team should
discuss the mineralÕs color and agree on a final color.
3 Teammates should
record the color in their journals.
A Second Test: Streaking
Another way to identify a mineral is to examine the color of
the streak when a mineral is rubbed across a flat surface. Sometimes the streak
has a different color than the mineral itself.
Materials
a porcelain tile (the backs of porcelain tiles offer rough
surfaces on which to streak minerals, other similarly rough surfaces will work)
Procedures
1 Rub the mineral
across the back of a porcelain tile.
2 Have teammates
examine the color of the streak,ideally under sunlight.
3 If the mineral is
harder than the tile and leaves no streak, carefully scratch the mineral with a
nail.
4 The team should
discuss the streakÕs color (or the scratch caused by the nail) and agree on a
final color.
5 Teammates should
record the color in their journals.
A Third Test: Hardness (Mohs Test)
Although most minerals may feel equally hard to our touch,
their hardness actually varies. In 1812, a German mineralogist, Friedrich Mohs,
developed a scale of hardness with which to classify minerals. The scale ranges
from 1 to 10, with 1 being talc and 10 being diamond.
The table to the right lists standard minerals by MohsÕ
scale and common items that are their equivalent in hardness.
Be careful if your test requires a nail, knife blade, or
steel file. These can easily slip off the mineral being tested and cause
injury!
Materials
copper coin
iron nail
glass tumbler
penknife blade
steel file
sandpaper
Procedures
1 Scratch your
mineral with your fingernail. If your fingernail scratches the mineral, the
mineral has a hardness of 2.
2 Otherwise, scratch
the mineral with a copper coin. If your mineral is scratched, it has a hardness
of 3.
3 Otherwise,
continue scratching your mineral with increasingly hard objects (use the
objects listed in the table above) until one scratches it. The corresponding
hardness number in the first column is the hardness of your mineral.
4 Teammates should
record the hardness of their mineral in their journals.
MohsÕ Common Equivalent scale Mineral
1 Talc none
2 Gypsum fingernail
3 Calcite copper coin
4 Fluorite iron nail
5 Apatite glass
6 Orthoclase penknife blade
7 Quartz steel file
8 Topaz sandpaper
9 Corundum none
10 Diamond none
Identify Your Mineral
Refer to the Common Mineral Identification Chart. Identify
the mineral whose color, hardness, and streak characteristics are most like
your results.
This is the name of your mineral.
The Common Mineral Identification Chart does not list all
minerals, so if you do not find a mineral in the chart with the same color,
hardness, and streak characteristics of your mineral, it is possible that your
mineral is not listed here. If you cannot find a match, ask your teacher for
help. You might want to ask a local amateur or professional geologist to help
you identify it.
The chart is available as PDF only.
An Additional Test: The Carbonate Test
You can test your mineral to see if it is a carbonate, an
important group of minerals that contain carbon and oxygen. The chief carbonate
mineral is calcite, from which limestone and marble are made. Limestone and
related carbonate rocks comprise 13 to 21 percent of the sedimentary rocks
exposed on the surface of the land. Carbonates are soft and often whitish in
color. Chalk, for example, is a carbonate. A distinguishing characteristic of
carbonates is the way they react to acid. An acid solution, if strong enough,
can dissolve carbonates and weaker solutions make them bubble and fizz, because
of the release of carbon dioxide as the carbonate dissolves.
You can test your mineral for carbonates by dropping some
vinegar (a mild acid) on it. You should also examine the mineral with a
magnifying glass to observe reactions that are too faint for the unaided eye.
You may want to practice the procedure on a piece of blackboard chalk.
An Additional Test: Magnetism
Hold a small magnet next to your mineral. Is the mineral
magnetic? Record
your finding in your journal.
Special Characteristics
Look for other special characteristics of your mineral. Is it
glassy? Metallic?
Silky? Does it feel greasy? Soapy? How does light interact
with your mineral?
Is it translucent? Transparent?
Record your observations in your journal.
Тесты на наличие минералов
(Experiences with minerals)
Как
вы можете
определить минерал
в обломке
породы?
Геологи
изучают широкий
спектр
характеристик
для определения
минералов. Вы
можете
провести
серию простых
опытов в
классе для
определения
минералов в
породах,
которые есть
у вас. Проведите
следующие
опыты,
запишите
результаты и
сравните их с
Таблицей
определения
простых минералов
для
определения
ваших
минералов.
Занесите
результаты
ваших опытов
в свой Журнал
ГлобалЛаб.
Опыт первый:
цвет
Часто
вы можете
определить
минерал по
его цвету,
хотя не у
всех
минералов
есть характерные
цвета.
Руководство
по
исследованию
материала
горных пород 1 Каждый
член команды
должен
внимательно
изучить цвет
(выбранного)
минерала, в
идеале это
следует
делать при
солнечном
свете. 2 Команда
должна
изучить цвет
минерала и договориться
о том, какого
же он цвета. 3 Члены
команды
должны
записать
этот цвет в свои
журналы.
Опыт второй:
отслаивание
Другим
способом
определения
минерала является
изучение
цвета штриха,
при натирании
плоской
поверхности
минералом.
Иногда слои
имеют цвет,
отличный от
цвета самого
минерала.
Исследование
материала
фарфоровая
пластина
1 Потрите
минерал о
фарфоровую
пластину
2 Члены
команды
должны
изучить цвет
слоя; предоставьте
для
нанесения
слоя грубую
поверхность
3 Если
минерал
жестче, чем
пластина и не
оставляет
следа,
аккуратно
нанесите на
минерал
царапины
гвоздем.
4 Команда
должна
обсудить
цвет слоя
(или нанесенной
гвоздем
царапины) и
договоритесь
о том, каков
цвет.
5 Члены
команды
должны
записать
этот цвет в свои
журналы.
Опыт третий:
жесткость
Хотя
на ощупь
большинство
минералов
одинаково
жестки, на
самом деле их
жесткость
различна. В 1812 г.
немецкий
исследователь
минералов
Фридрих Мохс
разработал
шкалу
жесткости
для
классификации
минералов.
Шкала имеет
деления от 1
до 10, где 1 – это
тальк, а 10 – это
алмаз. В
табличке справа
перечислены
типичные
минералы по шкале
Мохса и
различные
предметы,
являющиеся
их
эквивалентами
по жесткости
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.
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Материалы
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Порядок
работы
|
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Медная
монета
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1
|
Поцарапайте
минерал
ногтем, если
остаются
царапины, то
у минерала
жесткость 2
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Железный
гвоздь
|
2
|
В противном случае, поцарапайте минерал медной монетой. Если
остаются
царапины, то
у него
жесткость 3.
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|
Стеклянный
стакан
Лезвие
перочинного
ножа
Стальной
напильник
Наждачная
бумага
|
3
|
Если
нет, то
продолжайте
царапать
минерал все
более
жесткими предметами
(используйте
предметы,
перечисленные
в таблице
выше), пока не
появятся царапины.
Соответствующий
показатель
жесткости в
первой
колонке –
это
жесткость
вашего
минерала
|
|
|
4
|
Члены
команды
должны
записать
жесткость своих
минералов в
свои
журналы
|
Определите свой минерал
Обратитесь
к Таблице
определения
простых
минералов.
Определите
минерал, чей
цвет,
жесткость и слой
наиболее
схожи с
вашими
результатами.
Так вы
узнаете
название
своего минерала.
Таблица
определения
простых
минералов не
содержит все
минералы,
поэтому если
вы не найдете
минерал с
характеристиками
цвета,
жесткости и
слоя вашего
минерала, то,
возможно, вашего
минерала в
таблице нет.
Если не
можете найти
эквивалента,
попросите
помощи у преподавателя.
Можете
привлечь
местного
геолога
любителя или
профессионала
для определения
минерала.
|
Шкала
Мохса
|
Минерал
|
Эквивалент
|
|
1
|
Тальк
|
нет
|
|
2
|
Гипс
|
ноготь
|
|
3
|
Кальцит
|
медная
монета
|
|
4
|
Плавиковый
шпат
|
железный
гвоздь
|
|
5
|
Апатит
|
стекло
|
|
6
|
Ортоклаз
|
лезвие
перочинного
ножа
|
|
7
|
Кварц
|
стальной
напильник
|
|
8
|
Топаз
|
наждачная
бумага
|
|
9
|
Корунд
|
нет
|
|
10
|
Алмаз
|
нет
|
Будьте осторожны,
если для опыта нужен гвоздь,
лезвие ножа или стальной напильник.
Они
могут легко
соскользнуть
с минерала и поранить
кожу!
Week IIA. The Rock Cycle: The Layers of Earth (student reading)
Most of the EarthÕs rocky surface –the crust -- is just a thin layer on the EarthÕs surface. It makes up
the continents and the ocean floors. It is thinnest under the oceans
(6–11 km) and thickest under the largest mountain ranges (up to 70 km).
You can get a sense of how thin the rocky crust is by
drawing a large circle; the EarthÕs crust is proportionately even thinner than
the width of the circleÕs chalk line. You can also peel an apple – in
this case the thin peel represents the crust.
Continental crust and oceanic crust differ. The continental crust is 33 km thick and light, so
it floats on the lower layers. It is made up largely of granite and sedimentary
layers. It is much deeper under mountains. The oceanic crust is thinner (10
km), more dense, and made of basalt, a darker volcanic mineral.
From USGS
The crust plates slide slowly about on a much thicker thick
layer of rock called the mantle.
The mantle is about 2,900 km thick and makes up about 80% of the planetÕs
entire volume. How do scientists know when they have reached the mantle? The
rock in the mantle is so hot that it is often partially molten.
In a volcanic explosion, or in a situation in which rocks
crack, material comes from the mantle through the crust and cools on the
surface.
Under the mantle in the EarthÕs core is a dense ball of elements such as nickel and
iron. Temperatures within the core reach 3,700¼C.
lithos is Greek for ÒrockÓ or Òstone,Ó and sphairais Greek for ÒglobeÓ
How Do Scientists Know? Listening to Waves as They Pass
Through Earth Materials
When there is an earthquake, scientists have an opportunity
to listen to the way the energy waves of the earthquake travel through
different parts of the Earth's crust, mantle, and core. Adding waves together
from many earthquakes, they generate a three-dimensional model of the Earth.
One type of seismic wave can only move through solid rock
and not through liquid. It moves particles up and down or side to side.
Another type of wave generated by an earthquake moves in the
direction it is being "pushed".
This wave goes through both liquids and solids.
Sonar can generate waves through the Earth, too, for nearby
materials
http://www.geo.mtu.edu/UPSeis/making.html
.
Week IIA. The Rock Cycle: Introducing Continents (teachers)
1. Using the world map, have students explore EarthÕs
major land formations—its continents.
The goal of this initial discussion is to draw out some
general observations about the amount of land on Earth and its distribution.
Students can try to estimate the relative amounts of land and water on Earth,
and can describe the major patterns of land masses.
Continental shelves are less understood than many geological
features, and may be worth underlining with your students. Continents are
actually larger than the areas visible above sea level. The land underwater
consists of continental shelves. Continental shelves slope gently from ocean
shores down to depths of about 180 meters. The land then slopes downward more
sharply into the oceanic depressions.
If the area of the continental shelves were included,
continents would account for 35 percent of the EarthÕs surface. These shelves
explain why England is part of Europe and New Zealand is part of the Australian
continent.
2.
Have student teams brainstorm what
defines a continent.
For example, why is Australia a continent? Why is England a
part of Europe and New Zealand a part of the Australian continent? To what continent
does Japan belong? Where do continents begin and end? Antarctica at the South
Pole is a continent. Why is the Arctic at the North Pole not a continent? The
answer is at least partly historical convention. (see http://en.wikipedia.org/wiki/Continent)
3. Ask students to place themselves on a GL Continent in their journal. Have a discussion of what
their placement appears to mean.
They will see an unlabeled version of this map.
Labeled picture for teacher version
What difference does it make to be:
On a certain place in a watershed?
(e.g. a mountain origin of a river or the delta?)
On one side of a mountain or
another?
Near an old mountain range or a new
one?
4. Finally help students put the continents in
perspective by reviewing or assigning the reading of the structure of the
earth.
Homework: (Russian only) Student text GEO 3-7.
Week IIA. The Rock Cycle:
Locating Our Study Site on the GL Continent
(student journal)
Background
The Earth presently has seven continents. Continents have
important features, including:
1. Large slabs of bedrock, called shields, and their
eroded version, platforms. These can be found in Canada, the high plains of
North America, the interior of Australia, and the high plateaus of Africa and
Asia. A lot of land gets added to the edges of these shields.
2. A continental shelf, the area sloping from land
into the ocean. Continents are actually larger than the areas visible above sea
level. The land underwater consists of continental shelves.
3. Long belts of mountains around the shields. Mountain
building (orogenesis) occurs when tectonic plates disturb the crust, when one
landmass pushes into another, or when oceanic plates are drawn under another
plate.
4. Glaciers in the highest sections of mountains.
5. Sedimentary basins, which are low areas filled
with sedimentary rock from present or ancient seas.
6. A major drainage river
7. A delta where the river spreads out as it enters
the ocean
8. Rocky shores and sand beaches
9. A rain shadow on one side of a mountain ridge, creating drier land on
the other side.
The
Activity
In this activity, you can locate yourself on a drawing of a
continent. It has been simplified
to show typical continental features. It includes the land beneath the
continent, as it is important, too!
Answer the following questions in your GL Journal.
1. Place numbers from 2-7 on the continent outline below.
(#1 is usually hidden from view.)
Hint about #6: Where might the weather come from, if North
is towards the top of the page?
2. Where on this Òtypical continentÓ might your town,
school, and study site be best located? Place a mark there. Can you write
something about the effects of this location? (For example, is it moister or
drier colder or warmer?)
3. Choose another distant Global Lab school and decide where
it might reasonably be placed. What are the advantages and disadvantages of its
location? To determine this, you can review the schools introductory data (e.g.
altitude), use Google Earth to fly to the site and look around or simply write
and ask them.
4. Are there important features you think have been left out
of the ÒGL continent?Ó If so, what are they? Why are they important?
Extra Credit:
Find places on the map where each kind of rock might be formed. Mark the
map with I for igneous, S for Sedimentary or M for metamorphic.
The Origin of Rocks (students)
(For English version only. This piece has been largely
– but not entirely - covered
by Sergei and Boris's textbook.) Only add in what is missing in SL version.
Generally, rocks are
formed by one of three processes. They are classified into the following
categories:
Igneous
Igneous rocks are made from magma that rises toward the
EarthÕs surface and either stays underground (and is exposed later through
weathering) or erupts from volcanoes.
igneous
Ignis is Latin for Òfire.Ó
We turn on the ignition
in the car.
Metamorphic
Under extremely strong forces igneous and/or sedimentary
rocks can be reshaped into metamorphic rocks. Rocks change under pressure,
becoming more compact. They are significantly pressured in a side-to-side
direction.
Crystals and fossils in the rocks can be stretched and
distorted by this pressure. Rocks can also be changed by heating, for example,
when they are pressed against hot magma. In addition, they can be changed by
chemical activity. Water can dissolve minerals and then crystallize them within
a rock.
metamorphic
Meta is Greek for
Òchange.Ó
Morphos is Greek for Óshape.Ó
To ÒmetamorphoseÓ
means to change shape.
Sedimentary
Most surface rock (66%) is sedimentary, so you might expect
to find some sedimentary rock near you. There are three kinds of sedimentary
rock, depending on the source of the sediment.
Sediment comes from:
¥ the weathering of mountains;
¥ the compressed remains of organisms (limestone, for
example, is made from shells and coal is made from compressed vegetable
matter); or
¥ chemical processes that decompose rock.
sedimentary
Sedere is Latin for Òto sit.Ó Some people have sedentary
lifestyles.
Think
about:
IF
sedimentary – How did it get laid down? Water?
Weathering? Both?
IF
igneous –Was the magma intrusion or volcanic
IF
metamorphic – What changed the earlier made rock, heating, plate movement,
deep burial, all?
Week IIB. The Rock Cycle Stages
(Teachers guide)
The major processes that turn rocks into soil and again into
rock are:
¥ mountains are born; the movement of the EarthÕs crust up
or down;
¥ mountains are worn down; the erosion, or Òweathering,Ó of mountains into boulders,
rocks, sand, and eventually (with the addition of organic material) into soil;
¥ particles are carried by wind and water and laid down in
layers.
¥ material returns to the interior of the Earth where it is
reheated and returned to the surface as magma (liquid rock)
STEP ONE: Mountains are Born
Mountains are born when two continents collide or when magma
rises up from the EarthÕs core. As plates move, the EarthÕs crust stretches and
is crushed, cracked, folded, and crumbled. These movements also open new faults
through which magma from the mantle can come out and create a layer of igneous
rock.
Boulders fallen from the mountains are slowly worn away
by the stream.
STEP TWO: Mountains are Worn Down (weathering)
As soon as they are formed, mountains begin to be worn down,
"weathered" by ice, water, and wind into smaller particles. We tend
to think of large mountains as eternal, but whole mountain chains have come and
gone in EarthÕs history. The Appalachian Mountains in the United States were
once as tall and large as the Rockies, but have been weathered down to their
present gentle rises.
The speed at which weathering occurs depends on a number of
factors.
Some types of rock are harder than others. Hot and humid
climates break down rocks more quickly. Some land is shaped so that water and
wind can get at the rock more easily, and areas vary in the presence of
organisms and plants that get into cracks in the rocks or live on the surface
and make soil. Some soil-making processes called ÒweatheringÓ are shown in
these photographs.
The hard volcanic core of this mountain remains after the
surrounding material has eroded away.
Weather and water grind rocks down boulders into silt, sand,
and clay.
Physical (or mechanical) weathering occurs when
temperature changes cause cracking. Water then gets into the cracks, freezes
into ice, and expands to break the rock further. Cycles of cooling and warming
are among the most powerful forces for breaking down rocks. But sometimes the
material is so hard\to break down that it remains solid while the material all
around it has been eroded. This is true of the cores of old volcanoes.
Chemical weathering creates the smaller particles of
soil by changing rockÕs chemical nature. Water from rain and rivers,
combined with certain atmospheric gases, forms weak acids that wear down rocks. For example, water combines with carbon dioxide in
the air and produces carbonic acid. Carbonic acid can react with some minerals
inside rocks to cause disintegration and decomposition.
Biological weathering. Biological organisms promote
disintegration too. Lichens and moss are known as true pioneers because they
are the first plants to attach to rock surfaces. Later, complex plants send
their roots deep into the rocks, causing them to crack. This allows other types
of weathering to follow. The decayed remains of these plants become integrated
into soil and create a medium for the growth of more microorganisms.
Macroorganisms (for example, insects and rodents)
also play a role in disintegrating rock into soil. They burrow or tunnel among
small rocks, creating openings in which physical and chemical weathering can
take place. Earthworms process tiny particles of rock through their guts and
excrete them as soil, changing the pH of the soil as they go. The remains of
these animals are eventually decomposed into the soil as well. This
disintegration of rocks caused by the action of organisms (micro and macro) and
plants is called biological weathering.
STEP THREE: Particles are carried by wind and water and laid down in
layers. (Sedimentation)
Glaciers, moving water, and wind carry pieces of rocks that
collide and rub against each other, breaking off smaller and smaller particles.
These tiny particles are then deposited elsewhere as soil. Small particles and
organic matter are carried away by wind and water and set down in layered
sediments.
There are a few
useful rules of sedimentation that help us ÒreadÓ the Earth.
¥ Younger layers are laid down on top of older layers. For
example, as we travel into the Grand Canyon in the United States, we go back in
history, layer by layer, step by step.
¥ Layers are generally horizontal, and when we see abrupt
breaks in the layers, or folds, we know that strong geological forces have
shaped the breaks. We can piece together history by finding continuities and
discontinuities in the rock formations.
* Intrusion is younger than the stratified layers. Soil
formation is occurring all around the globe, but the rate of formation is
greater in regions where high temperatures, rainfall, and humidity are
prevalent. These conditions promote both chemical weathering because of the
abundance of water and biological weathering by supporting plant and animal
life.
¥ Younger layers are laid down on top of older layers. For
example, as we travel into the Grand Canyon in the United States, we go back in
history, layer by layer, step by step.
The Grand Canyon in the USA
STEP FOUR: Mountains are reborn. Material returns to the interior of the Earth where
it is reheated and returned to the surface as magma (liquid rock
This step is described in detail in the next week's work.
For a brief reference, see:
http://neic.usgs.gov/neis/qed/
Learning from Sand (background
reading)
by Linda Maston-McMurray, GL teacher, San Antonio, Texas
What can you learn from your sand?
¥ In studying sand, the first thing one can do is decide
whether the sand is made of fragments of once-living things (biogenic) or made
of nonliving material (abiogenic).
¥ Next, one can determine whether the sand came from an active continental edge
or a passive continental margin by the sand's composition. Sands from active
volcanic regions will have a higher percentage of dark minerals, giving them a
salt-and-pepper type appearance. Sands from passive regions may include some
dark minerals, but the percentage will be low. They are essentially
light-colored. You may find sands from areas that were active in the past. In
such cases, metamorphic rocks have eroded down and formed sands that appear to
be from an active edge, but in fact are not. Indeed, the margin ceased activity
many millions of years ago! See if you can determine why ÒpassiveÓ sand can
look Òactive.Ó
¥ Continents are basically composed of granite, and regardless of where the sand was formed, it
will reflect these granite origins, unless it is biogenic. Granite is light
colored and diverse ranging from grays to pinks.
¥ Oceanic crust is dark and basaltic. Therefore, sand formed in places like Iceland,
Hawaii, and Malaysia consists primarily of dark, heavy minerals. Those sands
are often high in basalt, olivine, or magnetite.
¥ Sands can be told apart by the degree to which they
have been sorted. Sands formed along
beaches tend to be well-sorted (with uniform grain size) and well-rounded (no
rough edges). Sands formed in deserts, lakes, and rivers may at first glance
appear the same, but they are usually poorly sorted. Shake a small sample of
such sand in a clear container and look underneath it. You will see that it
separates by grain size, and that the granules have many rough edges.
ÒRoundnessÓ does not mean that the grain is spherical. It means that,
regardless of shape, the grain has no (or very few) rough edges
Faster running water generally can carry larger pieces of
rock, so there is less likelihood of
finding only very fine grains in a swift river. The same principle applies to
beaches. Winter storms provide more energy to the water, so beach sand is
coarser in winter than in summer.
You can also determine the approximate slope of a beach
by looking at the sand. Beaches made of
coarser sand have steeper slopes than beaches made of fine grain sands. You can
get a sense of this by dumping a bucket of dry sand onto a flat surface and
measuring the angle of the slope that it forms. This also changes seasonally;
winter beaches will be just a bit steeper than summer beaches.
This piece was contributed by Global Lab teacher Linda
Maston-McMurry, formerly in San Antonio, Texas.
Understanding Clay, the smallest piece of rock
Every year the ocean moves the sand on Florida beaches,
sometimes into less convenient positions, and every year soil dredgers operate
large compressors to blow clean white sand back onto Florida beaches. One man
had been swept overboard three times in high waves as his platform with the
dredging machinery maneuvered large bays, such as the Chesapeake, or coastal
regions of Georgia and Florida. ÒClay,Ó he exploded, Òis the worst thing for
our machine! It stops it right up. But sand is easy; it moves right through. I
love sand, not clay!Ó
When minerals break down/ (weather), they produce small
particles – sand, silt, or, smallest still, clay.
You can see a chart of different sizes here:
http://en.wikipedia.org/wiki/Particle_size
Clay is made up of
particles less the 2 micron.
or 0.002 mm, which are even smaller than sand and silt. Clay particles
can be so small that it could take hundreds of years for them to settle from
the top to the bottom of a bottle of water; so small even water and air are
obstacles to their movement. Anything
they encounter slows them down!
Silt particles,
which are larger than clay particles, can be carried by swiftly flowing water
to the mouth of a river where they settle. Silt buildup creates islands and
blocks the mouths of rivers. The smaller clay particles settle out when the
water flow becomes slower yet.
Clay particles are flat and tend to interlock tightly like
tiny bricks. They bound together with water. You can easily slide in clay
because the attachment of the particles is so strong along planes.
[Picture of Vermont slate and rock]
Shale or slate (the metamorphic form of shale) is clay that
has been turned to stone. If you find shale or slate, you can imagine that the
area was once a calm, shallow water environment where the particles fell to the
bottomÉslowly.
Clay comes in many different colors because of the minerals
that attach easily to the small particles. Red, yellow, and red-brown colors indicate the presence of
iron.
Every year Pueblo potters of New Mexico, USA (above) go to
look for the right clay, a clay that fires well, takes a glaze, and is suitable
for pot-makers. Each tribe knows where its clay can be found, and the pots of
each pueblo reflect the differences in the clays.
If you heat clay in an oven without oxygen it will turn
blue-green or black. The black tones of the pottery made by Native American
potters of San Ildefonso Pueblo are famous in the United States. When rubbed
with a stone, those pots take on a shine. Clay in a body of water that cannot
get oxygen, such as a slow-moving estuary, is also black.
Some scientists think life may have begun in clays. Iron in
clays could capture nitrogen and carbon dioxide and make citric acid. Amino
acids, the building blocks of proteins, can be made from citric acids. IN fact,
one iron-rich mineral, when seen in cross-section, looks remarkably like DNA!
Week III: Geological Forces Over Time:
3A. Was It Always This Way?
The Geological Timeline (teacher guide)
In this activity,
students focus on change on a global scale, just as they explored change on
their study site. They revisit the importance of historical context when
studying any object, and they place the EarthÕs continents into such a
prospective. Students discuss the observations made by scientists and scholars
that indicate the EarthÕs surface is a dynamic and changing system.
StudentsÕ work in this activity helps prepare them for the
theory of plate tectonics. This theory offers plausible explanations for
scientific phenomena that puzzled Earth scientists for centuries.
Activity-at-a-Glance
¥ Students reconsider the value of investigating the history
of an object of study.
¥ Students consider the concept of geological time.
¥ Students solve ÒmysteriesÓ about how the continents
have changed over time.
Materials
Dating Rocks (Reading)
Continental Mysteries
Geological Timeline Global Lab
Classroom Management and Preparation
The beginning of the activity is done as a class discussion.
In Step 2, there are two versions of the Geological Timeline. One demands
somewhat more class time than the other, so you will want to be familiar with
both versions in order to decide which to use. Both this step and the
Continental Mysteries in Step 2 can be done as a class discussion or in student
teams. However you organize Steps 2 and 3, be sure to leave time for the class
discussion in Step 4.
Recommended Procedures
1. With students, revisit the importance of
placing an object of study into a historical context.
Accounting for how an object of study appears as it does
today often depends on reconstructing its past and the history of forces acting
upon it. Students themselves are a good example of change over time. Have they
changed over time? How? In size? In body development? In personality? In
knowledge? For how long have these changes been occurring? What evidence of
these changes could they provide an alien who just arrived on Earth?
2. Discuss geological time.
Geological time—covering hundreds of millions of
years—is difficult for the mind to comprehend. The Geological Timeline
supplement illustrates this very large number as a proportional 12-hour scale.
This is an opportunity to help students understand both timelines and the
visualization of large numbers. Younger students might want to start by
locating their birth years or other key dates in their community on the
timeline.
3. Challenge students to solve one or more
of the Continental Mysteries.
Is there evidence that continents changed over time? To
answer this question, students will consider the same phenomena explored by scientists. The goal here
is to have students learn that even the continents themselves have changed. The
mysteries demand that students use their critical thinking skills to
hypothesize about the dramatic changes to the EarthÕs surface over the course
of many millions of years. The, students might arrive at a bold hypothesis:
that the locations of the continents relative to the equator and the poles have
changed over EarthÕs history. Later students will examine this hypothesis more
formally when they are introduced to the theory of plate tectonics.
Mystery 1: The Oceans of Kansas
During the late nineteenth century, practitioners of the
fledgling science of paleontology were rushing to what was then the Òwild westÓ
of America to dig up incredible troves of fossils. What they found in the area,
now the state of Kansas, were fossils of Mosasaurs and other extinct marine
life. Kansas is located in the middle of the North American continent, far from
seas or oceans. How did these fossils get to Kansas?
Continents have changed dramatically over time. Kansas, for example,
was once the floor of a large inland sea that extended up from what is now the
Gulf of Mexico. Sea animals died and were preserved on the floor. And when the
waters finally receded after millions of years, their fossils remained on dry
land. You may want to ÒsolveÓ Mystery 1as a class and then have student teams
work on the remaining three mysteries.
4. Thinking about the past
The Continental Mysteries may be hard for students, so we
suggest you take time at the end of class to discuss their hypotheses. The
important point is not the specifics of the mysteries themselves, but
developing in students a willingness to think creatively and critically about
evidence in order to hypothesize about prior events. In this case, we want
students to consider the concept of change on the scale of continents and over
immense spans of time.
There are many ways to extend the work on the Geological
Timeline in order to emphasize the use of timelines in general and the
construction of scales. For example, students can choose and construct another
scale with which to equate geological time. An example might be the length of
their classroom. Students could measure the length of the classroom and then
calculate where along this length the key dates of EarthÕs history would
appear.
How Do Scientists Know the Age of Rocks?
(Student Reading)
Pick up a rock,
any rock, and examine it. Can you see any way to determine its age? Is it ten
years or ten million years old? You cannot tell just by looking at it. For this
reason, scholars for nearly all of human history had no way of knowing the age
of the Earth or its rocks. Up to the 19th century, for example, many people in
Europe believed the Earth was only about 6,000 years old. Yet, to those who
looked, the Earth offered bizarre clues of a deeper past.
One such person was Leonardo da Vinci, the great artist and
engineer who was also an extraordinary scientist and observer of the world
around him. He had seen fossil remains of animals where they should not be. In
one of his notebooks, he asked,
Why do we find the bones of great fishes and oysters and
corals and various other shells and sea-snail on the high summits of mountains
by the sea, just as we find them in low seas?
—Leonardo Da Vinci
The Notebooks of Leonardo Da Vinci, Vol II (Jean Paul
Richter, ed.),
Dover Publications, Inc.: New York, 1975, p. 217
Fossil Monsters
An even more difficult puzzle was the discovery of the bones
of animals that no longer lived. In 1770, for example, the huge jaws of a
primeval beast were discovered in Holland (later identified as belonging to a
Mosasaurus) and elephant bones were discovered in Paris. These and other fossil
remains persuaded scholars that the EarthÕs past must have been quite different
from its present. In the 17th century, progress was made in dating rocks when
Nicolaus Steno, a Danish anatomist, discovered what would be called the law of
superposition. He realized that
the layers of rock closest to the surface generally were younger than those
underneath. In other words, the deeper the layer, the older the rocks.
In 1796, William Smith, an English surveyor, noticed that
the most distinctive characteristics of many rock layers were their fossils. He
concluded that layers of rock containing the same fossils were the same age.
Therefore, by indexing their fossils,
rocks, regardless of their composition or location, could be correlated with
each other by when they were made.
Listening to the Atoms
Scientists had discovered geological time and were able to
determine the relative ages of rocks, but the rocksÕ actual ages remained a
mystery until the twentieth century when scientists were able to peer inside
their atoms. Scientists first saw that living organisms contain carbon-12 and carbon-14 isotopes
in the same ratios. Isotopes are forms of the same element that have different
numbers of particles in their nuclei. Carbon-12 has
six neutrons and 6 protons, while carbon-14 has
8 neutrons. When an organism dies, however, the carbon-14 decays into another isotope—nitrogen-14. Most importantly, the carbon-14 decays at a constant rate; half the atoms
decay every 5,730 years, which is called the elementÕs half-life.
Therefore, by examining the ratio of carbon-14 atoms to carbon-12
atoms, scientists could determine the age of organismsÕ remains up to
about 70,000 years. In 1960, this feat, called radiocarbon dating, earned its discoverer, American chemist William
Frank Libby, the Nobel Prize for Chemistry.
Scientists then applied this dating technique to inorganic
materials like rocks. They were able to measure the decay of various isotopes
like uranium- 238 and thorium-232 in rocks to determine their absolute ages.
The half-life of uranium-238, for example, is 4.5 billion years. Based on this
science, we have been able to date rocks tens and hundreds of million years old
and have determined that the Earth itself is some
4.6 billion years old.
Like so many
other discoveries in science, our ability to date rocks is built on the careful
observations and scientific testing of many people, often over the course of
centuries. Maybe someday, you will make an observation or discovery that
will contribute to our understanding of our Earth and the universe we live in.
Continental Mysteries (student homework or
class discussion)
For each
mystery below, try to develop a hypothesis—a testable
explanation—for the evidence presented.
Mystery 1: The Oceans of Kansas
During the late nineteenth century, practitioners of the
very young science of paleontology were rushing to what was then the Òwild
westÓ of America to dig up incredible numbers of fossils. What they found in
the area, now the state of Kansas, were fossils of Mosasaurs and other extinct marine
life. Kansas is located in the middle of the North American continent, far from
seas or oceans. How did these fossils get to Kansas?
Mystery 2: The Reptiles of Antarctica
In the 1960s, scientists discovered fossils of a
Lystrosaurus, a mammal-like reptile that lived in the early Triassic Period.
What was remarkable about the discovery was not the fossils themselves, but
where they were found—on Antarctica! How could such a creature, which is
believed to have lived in swampy habitats, be found on the ice-swept continent
of Antarctica?
Reptiles could not survive the cold temperatures of
present-day Antarctica (they are poikilothermic). Therefore, the presence of
these fossils indicates to scientists that the continentÕs climate was once
warmer than it is today. As you learned in Unit I, climate is greatly
influenced by the intensity of available sunlight, and light intensity is
determined by location on the EarthÕs surface. Yet, Antarctica lies on the
South Pole where the Sun angle is low and, consequently, sunlight is not
intense.
Under what circumstance could the continent of Antarctica
receive much more sunlight than it does today?
Mystery 3: Was New York Too Hot for New Yorkers?
Geological and paleontological evidence has revealed a
curious phenomenon about the state of New York. Half a million years ago, New
York was a cold, polar-like landscape with glaciers. Two hundred and fifty
million years ago, its climate was hot and desert-like. Fifty million years
before this, its climate was tropical. Climate is greatly influenced by light
intensity, yet there is no evidence that the Sun was once significantly hotter
than it is today, or that it cooled down half a million years ago, only to warm
up again. How can New YorkÕs changing climate be explained?
Mystery 4: The Tropical Ferns of the Arctic
Just as the fossil record indicates that the climate of
Antarctica may have changed substantially over time, scientists made a similar
discovery on the North Pole. They found fossils of tropical ferns on the Arctic
island of Spitsbergen. How could land on both the North and South Poles have
had very different climates than the very cold climates they have today?
Mystery 5: The Migration into North America
The Native Americans in North America have been found to be
genetically similar to those people who live in parts of Asia. But between Asia and North America
there lies the Pacific Ocean. How
could they have crossed an ocean to reach America?
3B. The Movement of Plates (teacher or
student background reading)
Why does some land in Australia looks very much like land in
India?
How can the same kinds of fossil plants be found in
Antarctica and also found in Australia, and India, although they are separated
by oceans?
What
if at one time all the land masses were once joined together?
Alfred Wegener
(left), a German meteorologist, described this idea in a book published in
1915. People laughed at his presentation, but we now know that Wegener was
right. He based his theory on the evidence of shape, fossils, rock types,
patterns of glaciers, and records of climate long ago. (If you look at the
pieces at the end of this reading, you will see they fit together.)
The EarthÕs surface consists of eight large plates and
several small ones, all moving in different directions at the speed of a
growing fingernail.
For example, at one point North America was located near the
equator. You can image how different the climate was then.
The Earth's Engine
What force is moving the plates around the globe? Beneath the crusts, the
EarthÕs material is slowly rolling (the more technical term is ÒroilingÓ).
We call these big patterns of circulating magma Òconvection
patterns,Ó and they work on the same principles as boiling water on your stove
or big air circulation patterns in our weather. When matter is hot, it expands,
becomes lighter, and rises. As it cools, it contracts, becomes denser, and
sinks. As a result, there are places where magma is rising and spreading out
and there are other places where magma is sinking. In between, the magma is
moving horizontally.
The continents float on this unstable fluid. It is no wonder
they are pushed around like sheets of ice on turbulent water. Sometimes they
crash into one another, sometimes they are pulled apart, and sometimes they
grind past each other going in different directions.
What were the clues the scientist Wegener used to piece the
puzzle together?
1. Fossils are the
remains and impressions of ancient plants and animals preserved in layered
rock. Fossils of plankton were useful for reconstructing continental history.
They lived in colonies only during specific ages of Earth. Their locations can
be matched up. For example, a section of Australia can be matched to a section
in India by looking for these fossil plankton.
2. Other rock layers (strata) with certain characteristics
(volcanic ash, meteorite dust, glacial tills, changes in sea level, sand sizes,
ancient shell beds) can be
compared with one another and coordinated..
3. Patterns of magnetism. The final piece of
evidence that led to international acceptance of plate tectonic history came
from magnetic data taken in the 1960s. The movement of the EarthÕs liquid outer
core generates a magnetic field, and the core behaves like a magnet. Every half
million years the polarity of this magnet changes because the currents in the
EarthÕs core change. When liquid
magma rises from deep in the Earth and solidifies, the iron within lines up
with the magnetic field]. Essentially, the magnetic field present when the
magma solidifies is frozen into the rock.
The ocean is growing.
When a scientist went to measure the magnetic patterns of the Atlantic Ocean,
he got astonishing results: the magnetic patterns on either side of the
Atlantic Ridge (out of which new magma was slowly pouring) were mirror images
of each other. The pattern of stripes could be compared with stripes in known,
dated rocks. Each stripe represented sea floor created while the magnetic field
was steady for about a half-million years. Newer material was closest to the
ridge, and older material was located further away. So the sea floor was
obviously spreading apart! Long ago this process had split a large landmass
apart and created the Atlantic Ocean. The ocean is still growing!
When Plates Pull Apart
Where two plates are pulled apart, two things can happen. If
the break is in the ocean where the crust is thin, like in the Atlantic, fresh
liquid magma oozes out, filling the opening and making a ridge. If the break is
caused by magma rising under a continent, the continent can break apart.
First the magma ÒdomesÓ under the continent, lifting it up.
Then erosion extends the gap. There are signs that there was an unsuccessful
rift in the Great Lakes area of the United States. A rift is successfully
opening on the African continent. Usually the pressure to pull apart reveals
itself in a three-armed radiation pattern, where bodies of water are created in
the arms as water moves into the rift. Can you see where this is happening near
the Horn of Africa?
If a break happens where the crust is thick or no magma is
rising, deep trenches can occur. On land, this can cause deep lakes like Lake
Baikal that is so deep that it contains 10% of all the EarthÕs freshwater! If
this happens in the ocean, deep underwater trenches are formed such as the
Philippine trench that goes further below sea level than Mount Everest is above
sea level!
When Plates Meet
When continents encounter each other, several things can
happen. The plates can move alongside each other (causing a transform fault),
one can slide under the other (creating a subduction zone), or they can move
together and effectively join another (forming ridge axes).
When Two Plates Collide
Where two plates collide, the lighter one rides up on top of
the other. This causes frequent earthquakes as the plates buckle and bend. The
lower one is pushed down and its material is heated until it becomes liquid.
Most of 
this
liquid is then returned to the EarthÕs center. This area is called the Òsubduction zone.Ó Some of the hot
liquid is too light to continue down and melts its way up through the upper
plate and makes volcanoes. All around the Pacific, continental plates are
moving over heavier oceanic
plates.
A few miles inland, over the subduction zone, there are
often volcanoes: Fuji in Japan and Mt. Saint Helens in the United States are
examples. What are other examples? Can you see why the region around the
Pacific is called the ÒRing of Fire?Ó
The pushing of plates against each other also creates
spectacular mountain folds, even folds that double back upon themselves. India
was once a separate continent. It crashed into Asia and the impact created a
huge ridge axis called the Himalayas.
subduction
sub is Latin for Òunder,Ó ducere is Latin for Òto lead]
Mountains are Born
Mountains are born when two continents collide or when magma
rises up from the EarthÕs core. As plates move, the EarthÕs crust stretches and
is crushed, cracked, folded, and crumbled. These movements also open new faults
through which magma from the mantle can come out and create a layer of igneous
rock.
Resources
AMNH
Plate tectonics
Plate
tectonics http://ology.amnh.org/earth/plates/tour.html
A classroom exercise: Hands-On
Plate Tectonics
Ask your students to:
1. Place your hands palms down on a table to show the
interaction of tectonic plates. Thumbs tucked, fingers flat, the hands side by
side, press your hands hard together until they buckle upward. The hands are
two continents converging, colliding—making mountains. The Himalayan
mountains were made that way.
2. Placing the hands flat again, then slowly move them
apart. These are two plates separating, one on either side of a spreading
center. The Atlantic Ocean was made that way.
3. Slide one hand under another. This is subduction, a
geologic process in which one edge of a plate is forced below the edge of
another. Ocean floors are consumed that way.
4. Tuck your thumbs, fingers flat, palms again side by side,
and then slide one hand forward, one back, the index fingers rubbing. This is
the motion of a transform fault, a strike-slip fault such as the San Andreas
fault in California, USA.
Adapted from John McPheeÕs description of a teacher teaching
plate tectonics. (Assembling California, New York: Farrar, Straus & Giroux,
1993, pp. 16–17).
ASSEMBLING PANGAEA (journal)
You can either cut out the pieces and try to piece them
together, using cues, or draw lines connecting them
Изменяющееся лицо мира
(Changing face of the world?)
Рисунки
показывают
как
изменилась
поверхность
Земли за
тысячелетия.
На этих картах
континенты
выделены
темным
цветом, расширяющееся
морское дно
обозначено
серым, а океаны
белые.
Последняя
карта
показывает
прогноз того,
как Земля
может
выглядеть через
пятьдесят
миллионов
лет.
180 млн.
лет назад
участок суши,
называемый
Пангея, начал
распадаться.
По
восточному
побережью
Африки стали
появляться
морские пути,
а между
западной
Африкой и
Северной Америкой
начал
формироваться
Атлантический
океан. 
Около
140 млн. лет
назад стал
открываться
новый океан,
когда Южная
Америка и
Антарктика отделились
от Африки.
Северная
Америка продолжила
движение от
Европы, а
Атлантика расширялась
на север.
Индия
продолжила
двигаться в
сторону
евразийского
континента.
Illustrations from EARTH IN MOTION: The Concept of Plate
Tectonics, by Ronald V. Fodor, with diagrams by John C. Holden. Copyright © by
Ronald V. Fodor. By permission of Morrow Junior Books, a division of William Morrow
& Company, Inc.
Investigation 1
Шестьдесят
миллионов
лет назад
наши современные
континенты
стали
узнаваемы.
Индия
продолжала
свой путь на
север.
Австралия и
Антарктика
отделились
друг от
друга, как и
Мадагаскар
от Африки.
Атлантический
океан продолжил
расширяться.
http://pubs.usgs.gov/gip/dynamic/historical.html
Geological Time Circle [journal]
The position on a
clock can represents a location in time. You can place important events in
earth history on a 12-hour time
circle by drawing a letter or a small picture/icon in the right time position.
Before you start,
or read further, write down your prediction of when humans appeared in the time
line.
_______________
I. The First Eleven Hours
A 4,500 million years (00:00)
The Earth is
formed.
B 4,300 million years (FIRST EVENT) (00:32)
Radioactive and
gravitational heating release water, and gases --methane, ammonia, hydrogen,
nitrogen, and carbon dioxide.
C 3,800 million years (1:52)
Water in the
atomosphere cools and condenses into oceans.
D 3,500 million years (2:40)
The first LIFE
appears—microscopic bacteria, the simplest form of life known today or in
the past. The first photosynthesis begins as tiny algae emit oxygen into the
atmosphere, strengthening the ozone layer.
E 1,500 million years (8:00)
The first
multicellular organisms appear.
F 545 million years (10:32)
First hard-bodied
organisms appear. Until now, nearly all organisms had been microscopic.
G 500 million years (10:40)
The first fish,
which are the first creatures to have backbones.
H 430 million years (10:51)
Algae begin to
live on land.
I 420 million years (10:52)
Millipedes are
the first land animals.
II. The Eleventh Hour
Do the same for
events in the last hour.
J 375 million
years (11:00)
The first
primitive sharks.
K 350 million years (11:04)
The first
amphibians, insects, and ferns,
the first plants
with roots.
L 300 million years (11:12)
The rise of
reptiles.
M 250 million years (11:20)
The Permian mass
extinction.
N 225 million years (11:24)
The first
dinosaurs.
O 200 million years (11:28)
The
supercontinent Pangaea starts to
break up as the
first mammals appear.
P 136 million years (11:38)
The first
primitive kangaroos.
Q 65 million years (11:49)
The dinosaurs
become extinct.
R 55 million years (11:51)
Rabbits evolve.
S 20 million years (11: 57)
Chimpanzees and
hominids evolve.
T 4 million years (11:59 and 39
seconds)
Human ancestors
stand up.
U .05 million years (11:59 and 59
seconds)
Homo sapiens, our
species, exists.
V .01 million years (11:59 and 59.5
seconds)
First permanent
human settlements and
the first use of
fire to cast copper and harden pottery.