Unit 11 Lesson 1 What Are the Oceans Like? Copyright © Houghton Mifflin Harcourt Publishing Company

Unit 11 Lesson 1 What Are the Oceans Like?

Copyright © Houghton Mifflin Harcourt Publishing Company




That’s a Lot of Water!





• Five oceans separate and surround Earth’s landmasses.

• They are, from largest to smallest, the Pacific, Atlantic, Indian, Southern, and Arctic Oceans.




• Oceans cover about 71% of Earth’s surface, almost three times the area that land covers.





Same Ocean, Different Water








1. Ocean water is salty, so you can’t drink it. The saltiness of water is its salinity.

• Salinity makes water denser, so boats float more easily in the ocean than they do in fresh water.

2. Exploring beneath the ocean’s surface requires SCUBA tanks for air and suits to keep warm.

3. Water pressure is the force of water pressing against whatever it surrounds.

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• At certain depths, a submersible—an underwater vehicle which provides air, light, and protection from water pressure and cold—must be used.

• Some places are too deep for human-driven submersibles, so robotic submersibles are used.








Is the Ocean Floor Flat?


• The floors of all the world’s oceans share roughly the same features.














Islands Come and Go


1. Oceanic trenches form where two plates meet and one sinks beneath the other, releasing magma at the boundary.


Islands Come and Go


2. Volcanic island chains form at plate boundaries and grow until they poke into the air, creating volcanic islands.

• The islands weather and erode over time and eventually disappear beneath the water again.


Islands Come and Go


3. In tropical regions, coral reefs form in shallow water around volcanic islands. These reefs can grow until they encircle an island.

• A reef can come out of the water, forming land that surrounds a lagoon of shallow water.

4. When a volcanic island sinks far enough to disappear, the ring-shaped coral, called an atoll, is left around the lagoon.


Islands Come and Go



Islands Come and Go






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Unit 11 Lesson 1 What Are the Oceans Like? Copyright © Houghton Mifflin Harcourt Publishing Company