1. Geological Evolution
Grade 8
Science

2. Geological
Evolution refers
to Earth’s
gradual
change over its
history.
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3. One of the ways in
which the Earth
evolves is through
plate tectonics,
which is the
process that
explains how
large pieces of
the Earth’s
outermost layer
move and
change.
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4. One aspect of plate
tectonics is the
Continental Drift
Theory, which states
that the gradual
shifting of Earth’s
plates causes
continents to change
their global positions
over time.
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5. The boundary formed by the collision
(coming together) of two plates is
called a convergent plate
boundary.
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6. The boundary formed between two
plates moving apart from each
other is called a divergent
boundary.
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7. Scientists believe that at one point in
Earth’s history all of the continents
were once connected to form a
gigantic land mass called Pangaea,
also known as the super-continent.
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8. Relative Dating
The use of information about rock
layers and the fossil record to
determine the age relationships
between rocks is called relative
dating.

9. The Law of Superposition is the
principal that states that each layer
of sedimentary rock is older than the
layer above it.
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10. Law of Superposition
In simple terms, this means that the
top layer of sedimentary rock is the
youngest and the bottom layer is
the oldest.
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11. An extrusion is an igneous rock layer
that forms when lava cools and
hardens on Earth’s surface.
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12. Extrusions are usually horizontal and
can be treated as a sedimentary
rock layer when trying to use
relative dating.
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13. An intrusion is when
magma cools and
hardens beneath
Earth’s surface.
These layers are not
horizontal and show
where magma has
broken through
sedimentary rock
layers.
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14. Intrusions are always younger than
the sedimentary rock layers they
have broken through.
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15. A fault is a break or
a crack in Earth’s
crust. A fault is
always younger
than the rock
layers that it
breaks through.
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16. An unconformity is where a newer
rock layer meets a much older rock
layer. It is a gap in the geological
record. It shows were some rock
layers have been lost due to
erosion.
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17. An index fossil is a fossil of an organism
that was present on Earth during a
short time range, but was common
on the Earth.
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18. Index fossils are used
to date rock layers,
because scientists
know that the rock
layer in which an
index fossil is found is
the same age as the
index fossil.
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