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A1.1.8 (HL)—Search for extraterrestrial life and water

Liquid water helps define planetary habitability because it supports chemistry for life, so astronomers examine habitable zones when searching for extraterrestrial organisms.

Syllabus
First assessment 2025
Objective
A1.1.8
Level
HL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceMay 2025
Most common paper—
Typical marks1

Common command terms

  • Identify
  • Interpret

Scoring notes

Common mistake
Treating location in the habitable zone as proof that life exists.

Recent exam appearances

May 2025Paper1A HL · TZ12[ 1 ]A1.1.8 (HL)—Search for extraterrestrial life and water
Practice this objective

Coverage 2025–2025 · Updated 14 Jul 2026

Concept essentials

  • Liquid water supports chemical interactions required by known life.
  • The habitable zone describes where liquid water may be possible.
  • Distance from a star influences planetary temperature.
  • Habitability evidence indicates possibility, not proof of life.
ConceptIB Biology HL