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Earth & space science · Grades 9–12

Rocks, plate boundaries and geological timescales

Igneous, sedimentary and metamorphic rocks describe formation processes. Material can move among these categories through several possible pathways.

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Prerequisites

Relevant school subject foundations and careful reasoning.

Study notes

Rock cycle

Igneous, sedimentary and metamorphic rocks describe formation processes. Material can move among these categories through several possible pathways.

Plates

Lithospheric plates move relative to one another. Boundary types influence deformation, volcanism and earthquake patterns but do not make every location identical.

Time

Relative dating orders events under geological principles; numerical ages require suitable measurements and models. Geological rates can vary over time.

Evidence

Combine structures, fossils where appropriate, mineral evidence and dating constraints. A single sample rarely describes an entire geological history.

Worked examples

Which process forms igneous rock?

Igneous origin involves molten material cooling and solidifying.

Solidification of melt

Which boundary has plates moving apart?

Divergence means separation.

Divergent

Check your understanding

  1. At a stated constant relative rate of 2 cm/year, find movement after 50 years.

  2. Why should a rate measured today not automatically be extended unchanged across all geological history?

  3. What does relative dating establish directly?

    1. Always mineral mass
    2. Event order
    3. Always an exact age in years
    4. Only sample colour

  4. Convert 3 million years into years.

Answers and marking guidance

Answers and marking notes
  1. 100 cm

    Distance=rate×time under the constant-rate model.

  2. Rates and conditions can change, and extrapolation needs evidence for persistence of the model.

    Credit temporal variability and modelling assumptions.

  3. Event order

    Relative dating orders events rather than necessarily measuring absolute time.

  4. 3000000 years

    A million is 1000000.

Further reading and review references

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