UNIT 8: THE EARTH
8.1 ROCKS, MINERALS,
AND SOILS
ROCKS, MINERALS, AND
SOILS
• 
The surface of the earth is covered in a layer
of rock. This is called the crust.
• 
Geologists: scientists who study rocks,
minerals, and the earth
ROCKS
• 
Rocks: clusters or groups of one or more
mineral stuck together.
• 
• 
ex) Granite, Basalt
There are three main types of rock:
• 
• 
• 
Igneous
Sedimentary
Metamorphic
MINERALS
• 
Minerals: different types of
materials that make up
rocks
• 
Each mineral is made of
one chemical substance.
• 
Minerals can form crystals
• 
ex) Granite is made of large
crystals from 3 types of minerals
SOIL
• 
Soil is made up of small particles of rock,
minerals, and the remains of organic matter.
• 
This organic matter ( remains of dead plants and
animals) is called humus.
• 
Many bacteria, fungi,
and small animals live
here.
• 
The bacteria and fungi
break down the
organic matter.
SOIL
• 
Particles in soils are
many different sizes.
• 
Sand is tiny and clay
is even smaller!
SOIL & WATER
• 
Some soils allow water to pass through them
very quickly while others take a long time.
• 
• 
• 
This depends on what the soil is made of.
Sandy soils drain quickly, clay doesn’t.
This matters a lot to farmers.
SOIL & WATER
• 
Soils that have poor drainage have particles
of clay that are small and stick together. This
makes the water unable to move.
• 
Soils that have larger
spaces between
them let water pass
through.
• 
Humus also helps to
hold water.
QUESTIONS
1. 
What is a geologist?
2. 
How can you tell the difference between a
rock and a mineral?
3. 
Name 3 kinds of minerals.
4. 
What do we call organic matter in soil?
8.2 CLASSIFICATION OF
ROCKS
IGNEOUS ROCKS
• 
Rocks are classified by the way they are
formed.
• 
Igneous Rocks: Rocks that are formed when
magma cools and solidifies.
MAGMA
• 
The Earth’s crust is made of solid rock, but
below it are melted, liquid rocks – magma.
IGNEOUS ROCKS
• 
Magma is a mixture of different minerals.
• 
This means magma can form different kinds of
rocks when it cools and becomes solid.
IGNEOUS ROCKS
• 
The way magma cools also affects the kind of
rock that is formed.
• 
When it cools deep
underground, it does
so very slowly. This
allows large crystals to
form.
• 
• 
Ex) Granite
When it cools closer to
the surface, it does so
quickly. This allows only
enough time for small
crystals to form.
IGNEOUS ROCKS
• 
When magma comes straight out of a hole in
the Earth’s surface, it cools even faster!
• 
There isn’t time for
any crystals to form.
• 
EX) Obsidian
VOLCANOES
• 
When magma reaches the surface of the
Earth it is called lava. The lava erupts from
volcanoes.
VOLCANOES
• 
Volcanoes are a rupture in the crust of the
Earth that allows lava, volcanic ash, and gas
to escape from a magma chamber below
the surface.
SEDIMENTARY ROCKS
SEDIMENT
• 
Sediment: little fragments (pieces) of rocks.
• 
Carried by rivers and eventually settle out of the
water, perhaps when the river reaches the ocean.
FORMING SEDIMENTARY
ROCKS
• 
Layers of sediment collect on the sea bed.
• 
As more layers are added, the weight of the
new layers presses the particles in the deeper
layers together.
• 
Solid rock is formed –
Sedimentary Rock
HOW DO YOU KNOW?
• 
How do you know a rock is a sedimentary
rock?
• 
• 
• 
It has layers
It could contain fossils.
It is made of grains or particles that are stuck
together. There are often tiny gaps in between the
grains, so we call it porous. Water can soak into these
gaps.
SANDSTONE
• 
Sandstone is a sedimentary rock formed when
grains of sand were pressed together.
LIMESTONE
• 
Limestone is a sedimentary rock formed from
little fragments of shells from animals, such as
corals.
• 
The grains are made of calcium carbonate.
GRAND CANYON
• 
The grand canyon contains about 40 layers of
sedimentary rock above a layer of metamorphic rocks.
• 
The youngest rocks are 200 million years old and the
oldest are almost 2 billion years old.
QUESTIONS
1. 
What clues would you look for to show a
rock is sedimentary?
2. 
Explain why sedimentary rocks are porous.
3. 
Explain why fossils are never found in igneous
rocks.
4. 
Pumice is an example of an igneous rock
that is porous. How do you think pumice
become porous?
8.8 FOSSILS
FOSSILS
• 
When animals and plants die, their bodies
may fall into sediments. Usually, they just
decay.
• 
Sometimes they
can become
part of
sedimentary
rock.
FOSSILS
• 
As the rock layers build up, the rock becomes
solid.
• 
The minerals
in the rock
can replace
the minerals
in parts of
the dead
bodies.
• 
This takes
millions of
years.
FOSSILS
• 
Fossils: Remains of living organisms that have
changed to rock.
• 
Fossils can also be made by imprints from
footprints or burrows made in wet sand or
mud.
• 
When more sediment is deposited on top of the
imprint, and the rock hardens, there may be a mark
left on the rock.
CLUES FROM FOSSILS
• 
Fossils can help us learn how a rock was
formed.
• 
Limestone has fossils from sea animals and
plants. So we know limestone was formed
under the sea.
COAL
• 
Coal sometimes contains fossils of ferns. So we
know coal was formed from trees that have
fallen in swamps.
FOSSILS
• 
Fossils tell us about the plants and animals that
lived millions of years ago.
• 
Some are very similar to those found today.
• 
This means that some types of plants and
animals have been around for millions of
years.
8.9 THE FOSSIL RECORD
THOUGHT EXPERIMENT
• 
A geologist is examining
different layers of rock, as
shown on the right. Using just
the image to the right, she is
able to determine at least 2
things.
• 
What are these 2 things?
• 
How do you know?
THOUGHT EXPERIMENT
• 
She is able to
determine:
• 
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The relative age of the
rocks
The relative age of the
fossils
THE FOSSIL RECORD
• 
The Fossil Record: The
order of different kinds of
fossils in different layers of
sedimentary rock.
• 
Tells us when different
species of animals and
plants first appeared on
the Earth.
• 
It shows us when a
species first appeared,
when it disappeared, and
how it changed over
time.
OLDEST FOSSILS
• 
The oldest fossils
found are bacteria
• 
They are about 3.5
billion years old
• 
3,500,000,000 years
old
THE FOSSIL RECORD
• 
Due to deposition, the
youngest layers of rock
are usually on top.
• 
The Law of Superposition:
The deeper a rock is, the
older it is.
• 
Therefore, the deeper the
rock in which a fossil is
found, the older it’ll be.
QUESTIONS
• 
What is different
about the top layers
compared to the
bottom layers?
• 
Would could this
mean?
EXTINCTIONS
• 
Sometimes, fossils found in older rocks are not
found in younger rocks.
• 
This indicates that the species of organism has
died out, they have become extinct.
MASS EXTINCTION
• 
The fossil record helps show us mass
extinctions.
• 
Mass extinctions: Events in Earth's history when
unusually large numbers of species die out
simultaneously or within a short amount of
time.