Summary
Oceans cover most of our planet — but Earth formed hot and dry, so where did all that water come from? Zachary Metz lays out the leading ideas, from icy comets and asteroids to gases released from deep inside the young Earth.
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Ages 7+
TED-Ed lessons move quickly and use rich vocabulary — best for grades 5–6 (some grade 4 with support). No content concerns; preview once for pace.
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Teaching resources
Discussion questions
Discussion
Earth is a water world — this lesson asks where all that water came from.
- Why is it surprising that Earth has so much water?
- What are two ideas scientists have for where the water came from?
- Why do scientists keep more than one possible explanation?
Quick work-a-long
Vocabulary: comet, asteroid, evidence, theory.
Try it: Draw two ways water might have reached early Earth. Which do you find more convincing, and why?