Extinction — Science definition

Defined in 2 courses:

Where it is taught

In use

Extinction — a species ceasing to exist — is read from the record too, and carefully, because the fossil record is patchy: a species vanishing from one sequence of layers may have died out, or moved, or simply stopped being preserved there.

Fossils, Rock Layers & Life History

Loss can mean fewer individuals, local disappearance, reduced genetic variation, or global extinction.

Biodiversity Loss

Questions using extinction

Problem 1

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 2

A population estimate falls from 500 to 350 under comparable methods. Find percent decline. Explain why this does not prove global extinction or identify a unique cause.
Answer and explanation

Decline=(500−350)/500=30%. Living individuals remain in the defined population, and the record alone cannot distinguish survival, reproduction, movement or the pressures affecting them.

Decline=(500−350)/500=30%.

Living individuals remain in the defined population, and the record alone cannot distinguish survival, reproduction, movement or the pressures affecting them.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical or environmental mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 3

Independent chapter check: A population estimate falls from500 to350 under comparable methods. Find percent decline. Explain why this does not prove global extinction or identify a unique cause.
Answer and explanation

Decline=(500−350)/500=30%. Living individuals remain in the defined population, and the record alone cannot distinguish survival, reproduction, movement or the pressures affecting them.

Decline=(500−350)/500=30%.

Living individuals remain in the defined population, and the record alone cannot distinguish survival, reproduction, movement or the pressures affecting them.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical or environmental mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

Problem 4

Explain why extinction is considered a more serious environmental problem than many others, such as air pollution.
Answer and explanation

Most environmental problems can be reversed — polluted air and water can be cleaned, and a warmed climate could eventually cool. Extinction is permanent: once the last members of a species die, that species and its unique genes and ecological role are gone forever and cannot be brought back. That irreversibility is what makes biodiversity loss especially serious.

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