Key Idea.
Section 1
The Blue Planet's Salt Trap
Earth looks like a "blue planet" from space because water covers most of its surface. But there is a catch. The vast majority of this water—about 97%—is found in the oceans.
This ocean water is salt water. Because it is so salty, humans cannot drink it, and farmers cannot use it to water crops. This means that while Earth has plenty of water, most of it is unusable for our daily needs.
Section 2
The Freshwater Treasure
The water that we can drink and use is called freshwater. However, freshwater makes up only a tiny slice of all the water on Earth.
Because it is so rare compared to salt water, freshwater is a precious resource. Every person, animal, and plant on land must share this very small supply to survive.
Section 3
The Hydrosphere System
Scientists have a name for all the water on Earth: the hydrosphere. This system includes every drop of water, no matter where it is or what form it takes.
The hydrosphere is not just the liquid water in oceans and rivers. It also includes the solid ice in glaciers, the invisible gas in the air, and the water hidden deep underground. All these forms are connected in one global system.
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Section 1
The Blue Planet's Salt Trap
Earth looks like a "blue planet" from space because water covers most of its surface. But there is a catch. The vast majority of this water—about 97%—is found in the oceans.
This ocean water is salt water. Because it is so salty, humans cannot drink it, and farmers cannot use it to water crops. This means that while Earth has plenty of water, most of it is unusable for our daily needs.
Section 2
The Freshwater Treasure
The water that we can drink and use is called freshwater. However, freshwater makes up only a tiny slice of all the water on Earth.
Because it is so rare compared to salt water, freshwater is a precious resource. Every person, animal, and plant on land must share this very small supply to survive.
Section 3
The Hydrosphere System
Scientists have a name for all the water on Earth: the hydrosphere. This system includes every drop of water, no matter where it is or what form it takes.
The hydrosphere is not just the liquid water in oceans and rivers. It also includes the solid ice in glaciers, the invisible gas in the air, and the water hidden deep underground. All these forms are connected in one global system.
Book overview
Jump across lessons in the current chapter without opening the full course modal.
Continue this chapter