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Earth science: where did Earth’s water come from?

Explore the fascinating theories behind the origin of Earth's water through a listening comprehension exercise. Practice C1 vocabulary, conditional sentences, and water-related idioms.

Earth science: where did Earth’s water come from?
Photo by Daniel Sinoca / Unsplash

Summary

This C1 ESL lesson explores the fascinating question of where Earth's vast water supply originated. Students will engage with a captivating video to enhance listening comprehension, expand their scientific vocabulary, and practice advanced conditional sentences.

The lesson plan guides advanced learners through a journey from initial planetary formation to current theories involving comets and asteroids. Activities include a warm-up discussion on water's importance, a listening gap-fill exercise, vocabulary matching, grammar practice focused on Type 3 and mixed conditionals, and a speaking task to apply new knowledge and language.

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Activities

00:06 It has no taste, color, or smell, and we often look right through it.
00:12 It covers over 70% of the Earth,
00:15 cycling from the oceans and rivers to the clouds and back again.
00:20 It even makes up about 60% of our bodies.
00:24 With all this water around and inside us,
00:27 it's easy to take its presence for granted.
00:30 But in the rest of the solar system, liquid water is almost impossible to find.
00:36 So how did our planet end up with so much of this substance
00:40 and where did it come from?
00:42 As you probably know,
00:43 a water molecule consists of two basic parts.
00:47 Hydrogen, the simplest of all elements,
00:49 has been around since close to the beginning of our universe.
00:53 Oxygen entered the scene several hundred million years later
00:57 after stars began to form.
00:59 The massive pressure at the center of these fiery infernos was so great
01:05 that hydrogen atoms fused together to form helium.
01:09 Helium, in turn, fused to form heavier elements,
01:12 like beryllium, carbon, and oxygen in a process known as nucleosynthesis.
01:20 When stars eventually collapsed and exploded into supernovas,
01:25 these new elements were spread across the universe
01:29 and combined into new compounds, like the now familiar H2O.
01:34 These water molecules were present in the dusty cloud
01:37 that formed our solar system
01:39 and more collided with our planet after its formation.
01:43 But there's a big question that we don't have the answer to:
01:46 how much water arrived on Earth, and when?
01:50 If, as one theory goes,
01:52 relatively small amounts of water were present on Earth when the rock formed,
01:57 the high temperatures and lack of any surrounding atmosphere
02:00 would have caused it to evaporate back into space.
02:03 Water would have been unable to remain on the planet
02:06 until hundreds of millions of years later
02:08 when our first atmosphere formed through a process called outgassing.
02:13 This occurred when molten rock in the Earth's core
02:16 released volcanic gasses to the surface,
02:18 creating a layer that could then trap escaping water.
02:21 So how then did water get back to the planet?
02:24 Scientists have long suspected
02:26 that much of it was brought by ice-bearing comets,
02:29 or more likely asteroids that bombarded the Earth over millions of years.
02:34 Recent research has challenged this theory.
02:37 In examining carbonaceous chondrite meterorites
02:40 that formed shorty after the birth of our solar system,
02:43 scientists have found that not only did they contain water,
02:47 but their mineral chemical composition matched rocks on Earth
02:51 and samples from an asteroid that formed at the same time as our planet.
02:56 This suggests that the Earth may have accumulated
02:58 a substantial amount of water early on that was able to stay put,
03:02 despite the lack of an atmosphere,
03:04 though asteroids may have brought more over the eons.
03:08 If this turns out to be true,
03:09 life may have formed much earlier than previously thought.
03:13 So we do not yet definitively know whether the water on Earth
03:17 came from its initial formation,
03:19 later impacts,
03:20 or some combination of the two.
03:23 Regardless, the water that runs from our showers, drinking fountains, and faucets
03:28 is something that didn’t just come from a nearby lake or river,
03:32 but first underwent a cosmic and chaotic journey to get here.

Vocabulary focus

The vocabulary section introduces and reinforces advanced terms related to astronomy, geology, and general scientific discourse. Key terms include "take for granted," "consist of," "outgassing," "bombard," "accumulate," "definitively," "eons," and "chaotic." Students will practice these terms through matching definitions and using them in context.

Grammar focus

This lesson concentrates on Third Conditional and Mixed Conditionals (often Type 3 + Type 2). Students will practice constructing sentences to discuss hypothetical past situations and their hypothetical past or present results, such as "If Earth hadn't had a dense atmosphere early on, much of its initial water would have evaporated." and "If comets and asteroids hadn't delivered water, our planet would be much drier today." This reinforces advanced conditional structures in a scientific context.

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