Fossils, Rock Layers & Life History — Practice · Grade 7 Science

Chapter: Evolution, Evidence & Life History

What this practice covers

By the end of Fossils, Rock Layers & Life History you should be able to:

8 questions, written answer and multiple choice, each with a worked explanation.

Vocabulary used: fossil, trace fossil, relative age, extinction, fossil record.

Problem 1

Can a footprint be a fossil without a preserved body?
Answer and explanation

Yes. It can preserve evidence of an organism’s activity and is a trace fossil.

Problem 2

Does the relative order give exact years?
Answer and explanation

No. It gives an older-younger relationship under the assumptions; numerical ages need additional dating evidence.

Problem 3

Why can fossil absence be uncertain?
Answer and explanation

Preservation, exposure, and sampling vary, so an organism may leave no detected record.

Problem 4

Why is “newer means more perfect” not a scientific conclusion?
Answer and explanation

Perfection is not a defined biological measure, and evolution involves branching and context-dependent traits rather than one universal ranking.

Problem 5

Illustrative upright undisturbed layers: bottom contains Species A; middle A and B; top B. No numerical ages or complete regional survey are supplied. State relative order, describe detected species patterns, and qualify an extinction claim.
Answer and explanation

The bottom layer is relatively oldest and the top youngest under the stated assumptions. A is not detected in the top record, while B occurs in middle and top. This local pattern alone does not prove A became extinct everywhere or supply exact dates. Preservation, sampling, and other locations need consideration.

Order bottom before middle before top.

A is detected in lower two; B in upper two.

Separate local non-detection from global extinction.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 6

A real layer sequence is overturned. Can its present bottom automatically be called oldest?
Answer and explanation

No. The simple rule assumed upright undisturbed deposition. Investigate the geological history before assigning order.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 7

Which is trace evidence?
  1. A preserved footprint
  2. A graph axis
  3. A fictional budget
  4. A lens factor
Answer and explanation

A preserved footprint

A footprint records activity rather than preserving the whole body.

Problem 8

Why does one fossil collection not inventory every species that lived?
Answer and explanation

Preservation and exposure vary, and collections sample limited places and materials. Many organisms leave no detected fossil in that collection.

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