Biology • Year 11 • Module 3 • Lesson 10
Fossil Evidence
Lock in the core vocabulary, the principles of stratigraphy, the significance of transitional fossils, and the methods and limitations of radiometric dating.
1. Term–definition match
The eight definitions below are shuffled. In the right-hand column write the matching term from this list: fossil record, transitional fossil, relative dating, radiometric dating, stratigraphy, index fossil, superposition, half-life. 8 marks
| # | Definition (shuffled) | Matching term |
|---|---|---|
| 1.1 | The preserved remains and traces of past organisms, collectively. | |
| 1.2 | Determining the relative age of a rock layer by comparing its position to the layers above and below it. | |
| 1.3 | A fossil showing intermediate characteristics between an ancestral group and a derived group. | |
| 1.4 | The study of rock layers and their sequence, used to reconstruct relative geological time. | |
| 1.5 | Calculating absolute age using the known decay rate of a radioactive isotope. | |
| 1.6 | The principle that in an undisturbed rock sequence, deeper layers were deposited before the layers above them. | |
| 1.7 | A widely distributed fossil of a species that lived only during a specific time period, used to date rock layers. | |
| 1.8 | The time required for half of a radioactive parent isotope to decay into a daughter product. |
2. True or false — with correction
For each statement, circle T or F. If the statement is false, write the corrected version on the line below. 8 marks (1 for T/F, 1 for correction where needed)
2.1 In undisturbed rock strata, the deepest layers are the oldest. T / F
2.2 The absence of transitional fossils between two groups proves those groups are not related by common ancestry. T / F
2.3 Carbon-14 is the most appropriate isotope for dating rocks that are hundreds of millions of years old. T / F
2.4 Tiktaalik is an example of a transitional fossil showing both fish features and tetrapod-like features. T / F
2.5 Gaps in the fossil record completely undermine the reliability of fossil evidence for evolution. T / F
3. Function recall
Answer each question in 1–2 sentences using precise terms from the lesson. 8 marks (2 each)
3.1 How does stratigraphy allow scientists to make evolutionary inferences about fossils?
3.2 What is the difference between relative dating and radiometric dating?
3.3 Why does soft tissue rarely fossilise, and how does this limit the fossil record?
3.4 Why is Archaeopteryx important as a transitional fossil?
4. Cloze — complete the paragraph
Fill each blank with the correct word from the word bank below. Use each word once only. 8 marks
Word bank: absolute | decay | deeper | derived | gaps | sedimentary | superposition | transitional
Most body fossils form in environments where rapid burial preserves remains. The principle of states that in an undisturbed sequence, layers are older than those above. This gives scientists a relative age for fossils before any age can be measured. Radiometric dating uses the predictable of radioactive isotopes to estimate ages in years. A fossil shows a combination of ancestral features and more features, providing evidence of evolutionary transition. in the fossil record reflect preservation bias and do not invalidate the pattern already observed.
Q1 — Term–definition matches
1.1 fossil record • 1.2 relative dating • 1.3 transitional fossil • 1.4 stratigraphy • 1.5 radiometric dating • 1.6 superposition • 1.7 index fossil • 1.8 half-life.
Q2 — True / False with correction
2.1 True.
2.2 False. Correction: Absence of transitional fossils reflects preservation bias — fossilisation is rare and not every organism is preserved. Absence of a fossil is not evidence of non-relationship.
2.3 False. Correction: Carbon-14 is only useful for relatively recent once-living remains. For very old rocks, uranium-lead dating is used instead because uranium-238 has a much longer half-life appropriate for geological timescales.
2.4 True.
2.5 False. Correction: Gaps in the fossil record reflect that fossilisation is rare and preservation uneven. An incomplete record can still be strongly informative if the preserved pieces show a consistent pattern consistent with evolutionary theory.
Q3.1 — Stratigraphy and evolution
Stratigraphy arranges rock layers in time order using the principle of superposition. When fossils in different layers are compared, scientists observe that older layers contain different forms from younger layers — simpler or earlier forms below and more recently evolved groups above — consistent with descent with modification over time.
Q3.2 — Relative vs radiometric dating
Relative dating determines whether one fossil is older or younger than another by comparing the rock layers they are found in, without assigning a specific age in years. Radiometric dating calculates an absolute age in years by measuring the ratio of parent radioactive isotopes to daughter products and using the known half-life of the isotope.
Q3.3 — Why soft tissue rarely fossilises
Soft tissue decays rapidly and is not protected by mineral content, so it is rarely buried quickly enough and in the right conditions to be preserved. This means the fossil record is biased toward hard parts such as shells, bones and teeth, and many organisms with soft bodies leave no trace at all, creating gaps in the record.
Q3.4 — Why Archaeopteryx matters
Archaeopteryx has reptile-like features (teeth and a long bony tail) alongside bird-like features (feathers and wings). This combination is exactly what would be expected near the transition between theropod dinosaurs and early birds, linking these major groups with a predicted mix of ancestral and derived traits.
Q4 — Cloze answers (in order of blanks)
sedimentary • superposition • deeper • absolute • decay • transitional • derived • gaps