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Fossils, fossilisation and dating fossils sheet
4-mark answer frame

What is fossilisation? Explain how the age of fossils is determined.

How to lay out the answer. Follow the frame, then write it in your own words.

  1. 1 · Define. Fossils are remains or traces of ancient organisms. Fossilisation is the process by which they form.
  2. 2 · Explain how a fossil forms.
    • The dead organism is buried in mud or sand
    • Soft parts decay; hard parts remain
    • Sediment hardens into rock
    • Minerals replace the tissue (petrifaction)
  3. 3 · Explain dating. Radiocarbon dating (W. F. Libby): ¹⁴C decays after death with a half-life of 5730 years, so the ¹⁴C left gives the age. Uranium or potassium methods date older rocks.
  4. 4 · Link to daily life. The fossil tree trunks at Tiruvakkarai in Villupuram district are petrified wood.
  5. 5 · Close in one line. Fossils and their dates show the order in which life evolved.

Scoring tip: Write 'half-life 5730 years' and name Libby. Both are frequent 1-mark answers too.