Phenomenon
The Earth is a unique planet, even among its neighbors in the inner solar system, having not only a rocky structure but also oceans, an atmosphere and life! We've figured out how the rocky core of Earth formed, but we are still wondering about the other three "spheres" -- hydrosphere (oceans), atmosphere, and biosphere (life).
Question
Where did Earth's oceans and atmosphere come from?
Model Ideas
- The Earth was formed from space rocks, so the water for the oceans and gases for the atmosphere must have come from space rocks.
- There’s plenty of water in space rocks to have filled the Earth’s oceans.
- Volcanoes released and continue to release water vapor and gases from the interior of the Earth.
- Gases released from volcanoes thus created the atmosphere too.
- The water vapor (a gas) condensed and formed the oceans.
Overview
Transition In: After developing a model for the formation of the geosphere, we turn our attention to the other aspects of Earth, the ones that make it more pointedly unique--the atmosphere, the oceans, and life. How did these originate?
We remind ourselves of a few lingering questions about the formation of Earth and decide to next focus on the oceans and atmosphere. In offering some initial ideas, we come to the logical supposition that the air from the atmosphere and the water that fills the oceans came from the very space rocks (meteors and comets) that built Earth's rocky geosphere. But is it possible that rocks contain water, and furthermore, enough water to fill the oceans. Through a lab, we recognize that rocks in fact do contain water, albeit in miniscule amounts. We also read about the typical low water content of a meteor. But in recognizing that the mass of the oceans is a tiny, tiny fraction of the mass of the Earth, we begin to see how our model idea makes sense.
We next wonder how so much of the water made it to the surface. In studying volcanic outgassing as a possibility, we also stumble upon a mechanism for the formation of Earth's atmosphere. It would seem, then, that the hydrosphere (oceans) and atmosphere came out of the molten geosphere. We conclude the unit by writing an explanation for the formation of the Earth using our new model ideas in combination with the model we developed in the last unit.
Transition Out: After imagining an Earth with both atmosphere and oceans, we recognize the stage has been set for the evolution of life. But we're still wondering when and how life comes to out planet.
Advanced Planning
There's little preparation for this unit beyond one demo/laboratory and an optional check-in about Human Impacts. (See the end of the Learning Segment Table below and the PowerPoint for details on this latter activity.) The goal of the gypsum lab is for students to recognize that water can be stored in rocks. Read the preparatory and purchasing notes here and in the laboratory Teacher Guide and make sure your room is well ventilated. Gypsum can have a strong “fertilizer” odor.
1: Our Lingering Questions About Earth
Overview: We remind ourselves of our observations of Earth in order to return to other questions about how the Earth got to be the unique planet that it is. In doing so, we develop or remind ourselves of three key questions (two of which we’ll take up).
What we have figured out...We’ve essentially returned to the leftover pieces of our initial Driving Question. We’d like to know first where Earth’s oceans and atmosphere came from.
2: Initial Ideas - Origins of Oceans and Atmosphere
Overview: We offer some initial ideas about the formation of Earth’s oceans and atmosphere.
What we have figured out...We’ve explored some initial ideas but we’ve also recognized that we need more information.
3: Learning More Through Investigation / Gypsum Lab
Overview: We engage in a lab and then a series of readings in order to further explore how oceans and atmosphere formed.
What we have figured out...We’ve learned that yes, you can get enough water from space rocks to make an ocean!
4: Volcanic Outgassing
Overview: We are now wondering how water might have made it to the surface of the Earth to form the oceans. By engaging in a reading, we also come to realize that volcanic outgassing might also explain the origin of our atmosphere!
What we have figured out...We’ve generated some ideas about the central role of volcanism in releasing the gases that make up our oceans and atmosphere, and we have explicitly discussed condensation. We are now ready to re-group around our Driving Questions and finalize our model.
5: Finalizing Our Model
Overview: We work to generate and finalize our model for the formation of Earth’s oceans and atmosphere.
What we have figured out...We’ve finalized our model for the formation of Earth's oceans and atmosphere.
6: Letter to a Friend
Overview: We finish the unit by formally applying our model back to our original question and write a letter to a relative or friend explaining the origins of Earth.
What we have figured out...We’ve figured out that we have a pretty good sense of how three of the four “spheres” of Earth were formed.
Optional A: Human Impacts - Water
Human Impacts-Water
We delve into the importance of water in human civilization, leveraging what we know about the water cycle and relating that to problems around drinking water and agriculture.
We’ve tied our understanding of our model to the water cycle and the water cycle to conservation issues. This has helped us to connect our learning back to bigger questions about human impacts.
Download Resources
| Attachment | Size |
|---|---|
| Download All Atmosphere and Oceans (MBER-LE) Resources | 16.15 MB |