Eduqas GCSE Geology · 2.3

Geochronological Principles

50 revision questions with answers for 2.3 Geochronological Principles in Eduqas GCSE Geology (spec C480QS). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, Five Degrees, Associations, or read every question and answer below. Not official Eduqas material.

All 50 questions and answers

Question 1
What is relative dating?
Answer:
Placing events or rocks in sequence as older or younger without necessarily giving numerical ages.
Question 2
What is absolute dating?
Answer:
Estimating a numerical age, usually with an uncertainty, for a geological event or material.
Question 3
What does uniformitarianism mean?
Answer:
Processes observed today help us interpret geological evidence of similar processes in the past.
Question 4
How can present-day ripple formation help interpret ancient sandstone?
Answer:
Modern ripples show how moving water or wind forms comparable structures in ancient sediment.
Question 5
What is original horizontality?
Answer:
Sediments are generally deposited in approximately horizontal layers before later deformation.
Question 6
What is lateral continuity?
Answer:
A sedimentary layer originally extends sideways until it thins, ends or changes character.
Question 7
What is superposition?
Answer:
In an undisturbed sequence, younger sedimentary layers lie above older layers.
Question 8
What is the cross-cutting principle?
Answer:
A fault, intrusion or other feature that cuts a rock is younger than the rock it cuts.
Question 9
What is the principle of included fragments?
Answer:
A fragment included within a rock is older than the rock enclosing it.
Question 10
A dyke cuts beds A and B. Which is younger, the dyke or the beds?
Answer:
The dyke is younger than both beds it cuts.
Question 11
A pebble of granite occurs in conglomerate. Which formed first?
Answer:
The granite pebble's parent rock formed before the conglomerate.
Question 12
Three undisturbed beds A, B and C lie bottom to top. Put them in age order.
Answer:
Oldest to youngest: A, then B, then C.
Question 13
If a fault cuts three beds but not a younger overlying bed, when did it move?
Answer:
After the three cut beds formed and before the younger overlying bed was deposited, assuming no later reactivation.
Question 14
How does an unconformity affect relative dating?
Answer:
It shows a break in deposition and/or erosion between older underlying and younger overlying rocks.
Question 15
An intrusion cuts schist and is covered by undeformed sediment. State its relative age.
Answer:
Younger than the schist it cuts and older than the sediment that overlies it.
Question 16
Why is a numerical date alone not a relative-age explanation?
Answer:
Relative age states an event's sequence compared with other events and uses relationships as evidence.
Question 17
What is geological correlation?
Answer:
Matching rock layers of the same or similar age between different locations.
Question 18
What is a zone fossil?
Answer:
A fossil used to identify and correlate a limited interval of geological time.
Question 19
What makes a useful zone fossil?
Answer:
A short geological time range, wide distribution, abundance and features that allow recognition.
Question 20
Why is a fossil restricted to a short time interval useful for dating?
Answer:
Its presence narrows the possible age of the rock containing it.
Question 21
How can the same zone fossil in two distant beds help correlation?
Answer:
It suggests the beds overlap in age, although other evidence should also be considered.
Question 22
Which cephalopod groups are named in the specification?
Answer:
Goniatites, ceratites and ammonites.
Question 23
What feature distinguishes the named cephalopod groups for dating?
Answer:
Differences in the patterns of their shell suture lines.
Question 24
What is a suture line in an ammonoid fossil?
Answer:
The line where an internal chamber wall meets the outer shell.
Question 25
What features of graptolites are used to identify evolutionary changes?
Answer:
The number and arrangement of stipes and the shape or arrangement of thecae.
Question 26
What is a stipe in a graptolite?
Answer:
A branch of a graptolite colony bearing thecae.
Question 27
What is a theca in a graptolite?
Answer:
A small cup-like part of the colony that housed an individual organism.
Question 28
Why do evolutionary changes in fossils assist relative dating?
Answer:
Different forms lived during different intervals, allowing fossil-bearing beds to be placed in a sequence.
Question 29
Can a fossil be used to date a rock that is older than the organism?
Answer:
No. A body fossil occurs in material deposited after the organism existed, barring later reworking.
Question 30
Why should possible reworking be considered when using fossils?
Answer:
An older fossil can be eroded from its original rock and redeposited in younger sediment.
Question 31
What is radioactive decay?
Answer:
The spontaneous change of an unstable parent isotope into a daughter product over time.
Question 32
What is a half-life?
Answer:
The time taken for half of the remaining radioactive parent atoms to decay.
Question 33
After one half-life, what percentage of the original parent remains?
Answer:
50%.
Question 34
After two half-lives, what percentage of the original parent remains?
Answer:
25%.
Question 35
After three half-lives, what percentage of the original parent remains?
Answer:
12.5%.
Question 36
After four half-lives, what percentage of the original parent remains?
Answer:
6.25%.
Question 37
If 25% of parent remains, how many half-lives have passed?
Answer:
Two: 100% to 50% to 25%.
Question 38
A mineral retains 12.5% of its parent isotope. Its half-life is 400 Ma. Calculate its age.
Answer:
Three half-lives have elapsed; 3 x 400 Ma = 1,200 Ma, assuming a closed system.
Question 39
Assuming no initial daughter and a closed system, what percentage is daughter after two half-lives?
Answer:
75% daughter and 25% parent remain.
Question 40
Why is a closed-system assumption important in simple radiometric calculations?
Answer:
Loss or addition of parent or daughter material can change the ratio and distort the calculated age.
Question 41
Why might heating by an intrusion affect a radiometric date?
Answer:
Heating may disturb or reset the isotope system, so the measured date may reflect the later event.
Question 42
What does Ma mean?
Answer:
Millions of years ago, or million years as a duration when the context makes this clear.
Question 43
What is meant by deep time?
Answer:
The immense span of geological history, extending billions of years into the past.
Question 44
What approximate age of Earth is given in the specification?
Answer:
About 4.6 billion years.
Question 45
How did James Hutton contribute to the idea of deep time?
Answer:
His interpretation of geological processes and unconformities supported an Earth far older than a few thousand years.
Question 46
What did Archbishop Ussher use to estimate Earth's age?
Answer:
A chronology based on the Bible, producing a much younger estimate than modern geological evidence.
Question 47
Why did Kelvin's estimate differ from modern estimates?
Answer:
His cooling model did not account fully for internal heat sources such as radioactive decay.
Question 48
How did radioactive dating contribute to Holmes's estimate of Earth's age?
Answer:
Radioactive decay provided a numerical method indicating a much older Earth.
Question 49
How did Joly attempt to estimate Earth's age?
Answer:
He used the accumulation of salts in the oceans as the basis of an estimate.
Question 50
Why did estimates of Earth's age change over time?
Answer:
Methods and evidence improved, and later models incorporated processes earlier estimates had missed.

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Geochronological Principles

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