This lesson explores where Earth’s water came from and why it has stuck around for billions of years. Students examine the asteroid origin hypothesis and its supporting evidence, the roles of gravity, temperature, and atmosphere in water retention (with early Mars as a contrasting case), and the concept of the Goldilocks zone in the search for habitable exoplanets and extraterrestrial life.

Includes: 30-slide lesson presentation with Do Now starter, success criteria, embedded progress checks, and a discussion-question wrap-up, plus a two-page consolidation worksheet with exam-style practice and a self-check.

Suitable for: IB Biology HL, Topic A1.1 (AHL extension)
Format: Editable PowerPoint and Word documents, styled to match the rest of the A1.1 Water resource set