Geologic Time

Practice exam questions written by Timothy H. Heaton,
Professor of Earth Sciences, University of South Dakota

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  1. What is relative dating?
    Going on a date with a sibling or cousin.
    Establishing that something happened a very long time ago.
    Establishing a sequence of events.
    Placing a specific date on an event.
    The concept of radioactivity.

  2. If a dike protrudes through several layers of rock, what can we conclude?
    A batholith resides nearby.
    A volcano resides nearby.
    The dike formed before the rock layers.
    The rock layers formed before the dike.
    The rock layers are igneous.

  3. What is an unconformity?
    A sedimentary surface that represents a time gap in the sedimentary record.
    An offset of sedimentary layers along a fault.
    The boundary between two rock types such as sandstone and shale.
    The top of an anticlinal fold.
    Tilted (non-horizontal) strata.

  4. What is the meaning of 'superposition' in reference to a layered sequence of sedimentary rocks?
    The name of the highest layer.
    The name of a dike or other feature that cuts across the layers.
    The position of layers forced upward along a fault.
    The principle that the layers were originally horizontal.
    The principle that higher layers are younger.

  5. What is meant by the principal of original horizontality?
    All rocks were originally horizontal.
    Each layer of rock is older than the one above it.
    Foliation in metamorphic rocks was originally horizontal.
    Layers of sediment are deposited in a nearly horizontal orientation.
    The original crust of the earth was almost perfectly flat.

  6. If a sandstone in contact with a granite contains fragments of the granite, what can you infer?
    The sandstone and granite are the same age.
    The granite is younger than the sandstone.
    The granite is older than the sandstone.
    The granite was intruded into the sandstone.

  7. What do we call the feature left by a cycle involving deposition, then removal of previously-deposited sediment by erosion, then a return to deposition?
    Cross-cutting.
    Inclusion.
    Rock cycle.
    Superposition.
    Unconformity.

  8. Match rock type under an unconformity with the name of the unconformity.
    Rock type Unconformity
    Igneous rock.
    Metamorphic rock.
    Sedimentary strata parallel to the unconformity.
    Sedimentary strata not parallel to the unconformity.
    Angular unconformity.
    Disconformity.
    Nonconformity.

  9. Which of the following is not generally part of the formation of an angular unconformity?
    Erosion.
    Folding.
    Marine regression.
    Marine transgression.
    Metamorphism.

  10. Which principle frequently uses dikes and faults for establishing sequences of events?
    Cross-cutting relations.
    Faunal succession.
    Inclusions.
    Original horizontality.
    Superposition.

  11. Which principle involves the use of fossils to correlate rocks?
    Cross-cutting relations.
    Faunal succession.
    Inclusions.
    Original horizontality.
    Superposition.

  12. Which of the following dating processes is most accurate for calculating the age the earth?
    Heat loss from earth.
    Radioisotope dating.
    Rate of erosion.
    Saltiness of the ocean.
    Superposition.

  13. Which requirement for absolute dating is violated by the method of rates of sedimentation?
    Initial condition.
    Final condition.
    Mode of process.
    Rate of process.
    All of the above.

  14. Which requirement for absolute dating is violated by the method of ocean salinity?
    Initial condition.
    Final condition.
    Mode of process.
    Rate of process.
    All of the above.

  15. Which requirement for absolute dating is violated by the Lord Kelvin's method of heat loss from the earth?
    Initial condition.
    Final condition.
    Mode of process.
    Rate of process.
    All of the above.

  16. Match each nuclear change to the name given to that type of decay.
    Nuclear change Decay type
    Loss of a gamma ray.
    Loss of a helium nucleus.
    Loss of an electron.
    Gain of an electron.
    Atomic number +1, mass unchanged.
    Atomic number -1, mass unchanged.
    Atomic number -2, mass -4.
    Alpha decay.
    Beta decay.
    Electron capture.
    Gamma decay.

  17. What condition(s) effect the decay rate of radioisotopes?
    Bonding characteristics.
    Ionization.
    Pressure.
    Temperature.
    All of the above.
    None of the above.

  18. Match each radioactive parent isotope with its stable daughter isotope.
    Parent isotope Daughter isotope
    Carbon-14.
    Potassium-40.
    Rubidium-87.
    Thorium-232.
    Uranium-235.
    Uranium-238.
    Argon-40.
    Lead-206.
    Lead-207.
    Lead-208.
    Nitrogen-14.
    Strontium-87.

  19. What does the term 'half life' refer to?
    Half the time required for an atom of a given radioisotope to decay.
    Half the time required for all the atoms of a given radioisotope to decay.
    The time required for a decaying uranium atom to move half way toward becoming lead.
    The time required for half the atoms of a given radioisotope to decay.
    The time required for half of the nuclear material to leave an atom.

  20. Match each radioactive parent isotope with its half life.
    Parent isotope Half life
    Carbon-14.
    Potassium-40.
    Rubidium-87.
    Thorium-232.
    Uranium-235.
    Uranium-238.
    5730 years.
    0.7 billion years.
    1.3 billion years.
    4.5 billion years.
    14.1 billion years.
    47.0 billion years.

  21. If one billion atoms of a radioactive isotope are left for two half lives, about how many of these parent atoms will be left unchanged?
    1,000,000,000.
    500,000,000.
    333,333,333.
    250,000,000.
    None.

  22. If argon gas has escaped from a rock being dated by the Potassium-Argon method, what type of error is possible?
    It makes no difference in the determined age.
    The determined age will be too old.
    The determined age will be too young.
    The determined age can be too old, the same, or too young.

  23. Which method is used to date organic remains?
    Carbon-Nitrogen
    Potassium-Argon
    Rubidium-Strontium
    Thorium-Lead
    Uranium-Lead

  24. Which method was primarily used to establish the Geologic Time Scale?
    Carbon-Nitrogen
    Potassium-Argon
    Relative dating
    Rubidium-Strontium
    Uranium-Lead

  25. What does the term Paleozoic mean?
    Ancient life.
    Future life.
    Middle life.
    Recent life.
    Visible life.

  26. What time units are eras subdivided into?
    Days.
    Eons.
    Epochs.
    Periods.
    Years.

Please report any problems or errors to Dr. Heaton.