A Resource for
Teachers
Soils and Us
WORM
Digging deeper - finding out
more about soil
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Activity 7 - The things people do to improve
their soils
Background
Soils are in a delicate balance with nature. When they are continuously
cropped and nutrients are being taken from the soil by growing plants, the
condition of the soil will deteriorate. Soils need to be ‘conditioned’ with the
addition of organic matter and nutrients so that the balance is maintained.
Poorer quality acid soils can be improved through the addition of organic
matter, nutrients and lime (which reduces the acidity).
In this activity students interview a range of people who use the soil to find out
what things they do to ‘condition their soils’.
Students will need to think of people in their community
who use soil.
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Students will interview someone in their community who uses soil, for
example, a farmer, orchardist, flower grower, market gardener, home
gardener or a Landcare group member.
Students give their interviewees the background information that some soils
are better than others from Activity 6, then ask the person being interviewed
what things they do to look after and/or improve their soil.
Different groups of students could interview different land users.
When all the identified users have been interviewed, students share the
information that they have found out.
Information could be shared orally or with a drawing which is explained to
the rest of the class.
Wrap up
All the information researched could be displayed in a wall mural with each
group drawing and writing the results of their investigation about how people
improve and care for their soils.
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Soils and Us: A Teachers’ Resource
Activity 8 - How deep is soil?
Background
The earth’s crust is a very small part of the total make up of the earth. The
greatest depth that has been drilled is about 12 kilometres into the crust.
Scientists believe the very centre of the earth (the inner core) is a very dense
hot solid rock, while the next layer (the outer core) is liquid rock. The next
layer out from the outer core is the mantle, a hot plastic rock. The earth’s crust
floats on this hot layer. In a weak part of the mantle, for example where there
is a fault, hot magma can burst through and erupt onto the surface of the earth
to form a volcano and sometimes shower us with tephra (ash). The concept of
being able to dig a hole through the earth and come out the other side is a
‘myth’ that it is explored in this activity.
The equatorial circumference of the earth is 40,074 km, with a radius of
6,378 km. To relate these concepts of distance to your students use the nearest
town and how many times you would have to go there and back to have
covered the same distance.
Discussion
Use the book the “Diggyest Dog in the World” as motivation for this investigation.
Or you could ask your class: “How deep a hole do you think you can dig?”
and “Where do you think you would end up?”
After reading the book ask students to consider the idea - could you (or your
dog) dig right through the earth from one side to the other? Why or why not?
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Students write their ideas to this question on strips of paper and stick them
to a sheet for others to view.
Use this as a gauge for yourself to determine the attitudes and concepts that
you will be dealing with.
Ask students “How are we going to find out what is 50 centimetres under
the ground? One metre? Five metres? One kilometre? Five kilometres?”
(Young students may need visual references to comprehend these distances).
Accept all suggestions and then work logically through, eliminating ideas
that are not practical.
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Some suggestions
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Dig a deep hole or investigate a hole that has already been dug, for
example, at a building site, road excavation or fence line posthole.
View a bank side/road side cutting.
Research answers through the Internet, encyclopaedia, books and experts.
Discuss the diameter, radius and circumference of the earth.
Look at the percentage of the earth that is crust, mantle and core.
After your investigations it should be clear to the students that you cannot
dig from one side of the earth to the other. Although you can drill for a
very long way into the earth’s crust this is only a very small part of the
earth’s total make up.
Have the students return to their original statements on the strips of paper
and reconsider what they have written. If necessary they may need to alter
their original statement.
Wrap up
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Ask students what part of the earth is it that we are studying from - the
crust, mantle or core?
Reiterate that this is a small and fragile part of the earth that we are
responsible for. We must ensure that this very important resource that is
used by us today should be used sensibly and sustainably so that the future
generations that follow us will also be able to use it for their life on earth.
Return to some of the methods discovered in Activity 7 as a reminder of
some of the things that we can do.
crust
mantle
outer core
inner core
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Soils and Us: A Teachers’ Resource
Activity 9 - What are the major rock types?
This activity has been adapted for use in this unit through the permission of the
Southland Regional Council, where it first appeared in their Teaching Unit “The
Soils of Southland - Te Oneone o Murihiki”.
Background
There are three main types of rocks on earth: sedimentary, metamorphic
and igneous.
Sedimentary rocks are formed from sediment, especially rock fragments and
shells that have moved and been deposited in water. Examples of sedimentary
rocks include limestones, sandstones and mudstones.
Metamorphic rocks have been formed under pressure or high temperatures.
Examples of metamorphic rocks include schist, marble and slate.
Igneous rocks have formed from the cooling and hardening of molten volcanic
materials, for example, basalt. Materials from deep within the earth are called
plutonic igneous rock, for example granite, which has solidified under the
surface of the earth.
Students are to investigate the different types of rocks using edible models.
Please ask students to wash their hands before this activity.
Equipment
For each group of three to four students you will need:
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/2 cup of peanut butter
12 crackers
bread knife
12 chewy lollies (that can be squashed)
8 pieces of waxed paper
4 paper towels
1/ cup of melted chocolate
2
chocolate moulds
spoon.
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Methodology
1. Discuss the formation of sedimentary rocks with the students.
2. Let them make peanut butter/cracker stacks to show the layers in
sedimentary rocks.
3. Discuss the formation of metamorphic rocks. Have the students choose
three chewy lollies of different types and colours (the actual lolly not the
wrapper) and two pieces of waxed paper.
4. Unwrap the lollies and stack them on one piece of paper. This will be easier
if the lollies are warm.
5. Cover with the other piece of waxed paper and press down on top of the stack.
6. Look at the layers that have formed to represent metamorphic rocks.
7. Discuss the formation of igneous rocks. Have the students spoon melted
(molten) chocolate into the moulds. As it cools and hardens, it takes the
shape of the mould.
8. Have the students draw a diagram of the three different types of rocks.
9. Compare their rocks with real rocks.
Wrap up
Discuss the students’ diagrams and the formation of different rock types again,
comparing them with their models. Then let them devour their formations!
Variation
Complete just one type of rock formation per lesson and compare your
diagrams/drawings once all three-rock types have been explored. It is
important that the focus always returns to the formation of rocks in a highly
motivational activity such as this one as the students may focus on the model
making rather than the demonstration that the model is providing.
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Soils and Us: A Teachers’ Resource
Activities 10 and 11 - Investigation of the
soil horizons
Use the Compact Disc - ‘New Zealand Soils on CD’
Background
Having investigated that the earth’s crust is very small compared to the whole
earth, students are now going to investigate the characteristics of layers of soil
in a pit or road cutting or a site of erosion.
The shallow surface layer of the topsoil is the ‘O’ horizon, usually only a few
millimetres deep (under a forest environment it can be centimetres thick) and
contains organic matter, such as plant material.
The second layer down is the ‘A’ horizon, which is the dark organic rich layer,
which varies in depth from a few centimetres to about 30 cm depending on
soil type and location.
The third horizon down the soil profile is the ‘B’ horizon, normally the sub-soil
that can vary in depth from a few centimetres to several metres thick.
The ‘C’ horizon usually consists of the parent material and can be many metres
deep. Students will be looking to find examples of all of these horizons and
attempt to identify the parent material that the soil is formed from.
Many road cuttings in the hilly areas of the Region show multiple tephra layers
(volcanic ash) beneath the present day soil. Discuss volcanic eruptions and the
depths of the layers and what would be the effects of one of these eruptions if
it occurred next week – damage to structures, crops, pastures, water supplies
and disruption to transport and communication systems.
Action
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Visit a roadside cutting or take a soil sample
using an auger or make a substantial hole in
your school grounds or have a series of photos
of a cliff face or roadside cutting.
Students must be able to clearly view the layers
within the soil profile.
When selecting your site you must be aware
of safety issues if you are on the roadside
or if you are entering private property.
The purpose of the visit is to allow students to clearly view different soil
horizons. Get the students to examine the soil in detail. They should look
at the surrounding land use and investigate how the soil may have formed
in the environment that it has. Things to consider include slope angle,
topography, aspect and vegetation.
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Activities at the roadside cutting.
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Have students measure the depth (cm) of each layer or horizon that is
clearly visible.
Take soil samples from each horizon, labelling each sample according to its
respective placement, that is, ‘O’, ‘A’, ‘B’ and ‘C’.
Have students take notes about what they see in each horizon, in particular
any clues as to what may have influenced the soil make-up.
Take photos of the site and surrounding land use to refer back to.
Collect parent materials such as rock or sediments if present to investigate
back at school.
Have the students look around at the current land use and any other
geological features that might be important when considering the formation
of the soil.
Describe the soil structure in each horizon and record the different colours seen.
Complete a pH and soil textural test for each layer of the soil.
Back in class make a mural (to scale or as close to life size as possible) of the
cutting you visited.
Soil samples from each level could be glued on after a simple soil analysis has
been completed. Refer to Activity 2 of this unit.
Questions to investigate:
You will need to act as facilitator so that students ask questions that are most
important to them, but also so that they cover the range described below.
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Why has each layer formed to the depth and level that it has done?
Why isn’t the soil all the same colour?
How many layers did we see?
What types of soil do we think this might be?
Is the soil texture and structure the same all the way through?
Do soil colours change down the profile?
What things have happened in the geological history of New Zealand that
would be important when considering the layers that we see?
How has this soil formed?
Can we establish what the parent material is?
If we know what sort of parent material it is, what can we find out about
how these soils were formed?
How old do we think this soil is?
Wrap up
Students should make some tentative hypotheses when attempting to answer some
of the above questions. They should then use the following activities and the
results of their own investigations and research to determine what they can about
how the soil in the area that you visited was formed and will continue to form.
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Soils and Us: A Teachers’ Resource