Rock strata correlation – Solutions
Part 1
1. What is the principle of superposition? Explain why this cannot always apply to
rock strata samples taken.
This assumes that the layers at the top are younger than those below. In areas of
frequent earth movement, layers are disturbed and re-aligned. Also in areas where
humans have mined and excavated large sections of rock, this principle cannot be
applied.
2. When comparing rock strata from different locations, index fossils can be used
to help determine approximate ages. Explain how this is done.
Index fossils are those fossils that were present on earth for a limited time and were
found widely distributed. When these types of fossils are found in rock strata, their
known age makes it easier to estimate if a layer of rock is older of younger than
others.
3. Fossilised pollen grains are also used to assist when dating rock or soil sample.
Explain how these fossils can be used.
These fossils can provide information about the vegetation that existed at the time
when the deposit was laid down. This means scientists can construct a picture of the
climatic conditions prevailing at the time which may assist in working out the
approximate age.
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Part 2
1. When several rock strata samples are taken from one location and compared,
often the various layers no longer align – as shown in Series A and B. Suggest a
reason why this is so.
Earth movements, animal scavengers and human activity can all contribute to layers
of rock being realigned from their original position.
2. Look at all three rock strata and determine which is oldest and youngest. Explain
how you arrived at your answer.
Series A is the oldest and C is the youngest based on matching the layers
containing the same types of fossils. For example A1 matches with B5 and B3
matches with C8.
3. Are there any index fossils present? If so, list the layers that they are found in.
Yes in layers A1, B5 and B1, C6 and B3, C8.
4. Carbon-14 dating was used to date a fossil found in layer A5 at 50,000 years
old. What can you infer about the relative ages of B6 and C8?
They are younger than 50,000 years old because when the layers are correlated
both B6 and C8 are located above A5.
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