Lesson 8

8

Liquid Water & An Atmosphere

Where did Earth’s water and air come from?

As early Earth cooled, oceans and an atmosphere developed. This lesson covers the origins of water and air, the water cycle, and the conditions that made liquid water and life possible.

Click here to hear the lesson video

Key Ideas

• Early Earth had no oceans or atmosphere. These formed over time as the planet cooled.
• Volcanoes released gases that created Earth’s first atmosphere and water vapor.
• As Earth cooled, water vapor condensed into rain, forming the oceans.
• Earth’s gravity keeps both water and the atmosphere from escaping into space.
• Water on Earth moves through a continuous cycle: evaporation, condensation, precipitation, and collection.
• Liquid water and an atmosphere make Earth a planet where life can exist.

Spines

• DK's Science as You've Never Seen it Before:
• Visual Timelines: Life on Earth
  • pg. 11 (4.4 Billion Years Ago)
  • pg. 13 (Weaving an Airy Blanket)
• Mammoth Science: Water Cycle pg. 142, States of Matter pg. 8, Changing States pg. 10
• Alternative:
  • NASA Climate Kids: Water Cycle (https://climatekids.nasa.gov/water-cycle/)
  • NASA Climate Kids: Atmosphere (https://climatekids.nasa.gov/menu/atmosphere/)

Vocabulary

• Atmosphere: The layers of gases surrounding Earth, held by gravity; essential for weather, climate, and life.
• Water Cycle: The continuous movement of water through evaporation, condensation, precipitation, and collection.
• Evaporation: Liquid water absorbs heat and transforms into water vapor.
• Condensation: Water vapor cools and changes back into liquid, forming clouds and droplets.
• Precipitation: Water that falls from the atmosphere: rain, snow, sleet, or hail.
• Greenhouse Effect: The warming of Earth's surface when atmospheric gases trap heat from the sun.

Discussion Questions

1. What are the two major components Earth needed to have in order to support life?
   Sample Answer: Liquid water and an atmosphere (air).
2. Why is Earth’s position in the "habitable zone" so important for the existence of liquid water?
   Sample Answer: Earth is not too hot, so water doesn't boil away, and not too cold, so water doesn't stay frozen. This allows liquid water to exist.
3. What is "outgassing," and how did it contribute to Earth’s early environment?
   Sample Answer: Outgassing is when early volcanoes released gases like water vapor, carbon dioxide, and nitrogen. This process created Earth’s first atmosphere.
4. How does gravity help maintain the conditions necessary for life on our planet?
   Sample Answer: Gravity keeps water on Earth and holds the atmosphere in place. Without enough gravity, gases and water escape into space.

Digging Deeper

1. If Earth's volcanoes hadn't released those specific gases, or if our planet was significantly smaller, how might the development of life have been different?
   Sample Answer: Answers will vary.