Hydrosphere

Hydrosphere

Middle School

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Learning Objectives

• Develop a model to describe the major processes of the water cycle.

• Explain the roles of the sun's energy and gravity in the water cycle.

• Describe the distribution of fresh and salt water on Earth.

• Recognize the role of living organisms in transpiration and respiration.

Key Vocabulary

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Water Cycle

The continuous movement of water on, above, and below the surface of the Earth.

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Evaporation

The process where liquid water heats up and turns into a gas called water vapor.

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Transpiration

The process where plants absorb water from soil and then release it as vapor from leaves.

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Condensation

The process where water vapor in the air cools and changes back into liquid water droplets.

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Aquifer

An underground layer of rock or soil that holds a usable amount of fresh groundwater.

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Gravity

An invisible force that pulls matter, including water, downward toward the center of the Earth.

The Water Cycle

• The sun's heat causes surface water to evaporate into the atmosphere.

• Rising water vapor cools and condenses to form clouds.

• When cloud droplets get heavy, they fall to Earth as precipitation.

Multiple Choice

According to the water cycle, what happens after water vapor cools and forms clouds?

• It evaporates into the atmosphere.

• It falls back to Earth as precipitation.

• It is heated by the sun again.

• It turns directly into ice.

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Driving Forces of the Water Cycle

Solar Energy

• Energy from the sun is the primary force that powers the water cycle on our planet.

• This energy warms surface water, causing it to evaporate from oceans, lakes, and rivers into the atmosphere.

• It also drives transpiration, the process where plants release water vapor into the air.

Gravity

• Gravity is the other key force that plays a critical role in the water cycle.

• This force is responsible for pulling precipitation down from the clouds to Earth's surface.

• It also causes water to flow downhill, creating rivers and streams that return to the oceans.

Multiple Choice

What are the two primary forces that power the Earth's water cycle?

• Solar energy and gravity

• Wind and ocean currents

• Evaporation and precipitation

• Rivers and glaciers

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Role of Living Organisms in the Water Cycle

Plants

• ​Plants absorb water from the soil using their extensive root systems.

• ​​The water travels up through the plant to the leaves.

• ​It is then released as water vapor into the air through transpiration.

Animals & Decomposers

• ​Animals release water vapor into the atmosphere when they breathe, which is respiration.

• ​​When organisms die, decomposers like bacteria break down their organic material.

• ​This process releases water and nutrients back into the soil and atmosphere.

Multiple Choice

How do plants primarily release water vapor into the atmosphere?

• Through transpiration from their leaves

• By releasing it from their roots

• Through respiration, or breathing

• When they are broken down by decomposers

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Distribution of Earth's Water

• About 97% of Earth’s water is salt water found in our oceans.

• ​Only a small fraction of Earth's water, about 3%, is fresh water.

• Two-thirds of all fresh water is frozen in glaciers and ice sheets.

• Most unfrozen fresh water is groundwater stored in soil and rock layers.

Multiple Choice

Which statement accurately describes the distribution of water on Earth?

• Most of it is salt water found in oceans.

• It is mostly found as groundwater deep underground.

• Most of it is fresh water found in glaciers.

• It is evenly divided between fresh and salt water.

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Surface Water Systems

Rivers & Watersheds

• A river system has a main river and all the smaller streams, called tributaries, that flow into it.

• The watershed is the entire land area that collects and channels water into the river system.

• Watersheds are separated from each other by a high ridge of land which is known as a divide.

Ponds & Lakes

• Ponds and lakes are bodies of mostly still, fresh water that collect in low-lying areas on land.

• Unlike rivers that mainly move water, lakes and ponds act as important storage systems for fresh water.

• They are important because they hold a large amount of the fresh water available on the Earth's surface.

Multiple Choice

What is the term for the land area that supplies water to a river system?

• A watershed

• A divide

• A tributary

• A lake

Groundwater Systems

• Groundwater is fresh water stored in underground soil and rock layers.

• The ground has an unsaturated zone and a lower saturated zone.

• Wells are drilled into aquifers (an underground layer of rock or soil that stores ground water) to access this important water source.

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Multiple Choice

What is an aquifer?

• An underground layer of rock or soil that stores groundwater

• The top layer of soil where water first seeps in

• A well drilled to access water

• An underground river of fresh water

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Ocean Characteristics

• Salinity is the amount of salt, making seawater denser than freshwater.

• Ocean temperature is warmest near the equator and gets colder with depth.

• Water pressure increases with depth due to the weight of overlying water.

• The ocean floor has mountains (seamounts), canyons (trenches), and ridges.

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Multiple Choice

What is salinity a measure of?

• The amount of dissolved salts in water

• The temperature of the ocean water

• The weight of the water from the surface

• The types of features on the ocean floor

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Common Misconceptions

Misconception	Correction
Most of Earth's water is fresh and usable.	About 97% is salt water, and most fresh water is in glaciers.
The water cycle is a single, simple loop.	The water cycle is complex, with many pathways and storage areas.
Groundwater exists in large underground rivers.	Groundwater is held within porous rock and soil called aquifers.
The ocean floor is a flat, sandy basin.	The ocean floor has mountains, trenches, and volcanic ridges.

Multiple Choice

How does the process of transpiration move water from the soil to the atmosphere?

• Water is absorbed by roots, moves through the plant, and is released as vapor from leaves.

• Water is created in the leaves and then stored in the plant's stem.

• Water is absorbed by the leaves and is then released as vapor from the roots.

• Water is released from the roots directly into the atmosphere.

Multiple Choice

What is the main functional difference between a river system and a lake?

• A river system primarily moves water, while a lake primarily stores it.

• A river system contains still water, while a lake contains flowing water.

• A river system is found in low-lying areas, while a lake is on a ridge.

• A river system is separated by a tributary, while a lake is not.

Multiple Choice

If the force of gravity on Earth were significantly weaker, what is the most likely impact on the water cycle?

• Precipitation would not fall from clouds, and rivers would not flow downhill.

• Energy from the sun would be trapped within the atmosphere.

• Water would evaporate much faster from oceans and lakes.

• The sun's energy would no longer be able to warm the Earth's surface.

Multiple Choice

An underwater vehicle is exploring a deep ocean trench. Which conditions is it most likely to encounter?

• High pressure and cold water

• Low pressure and warm water

• High pressure and warm water

• Low pressure and cold water

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Summary

• The water cycle is a continuous process driven by solar energy and gravity.

• Living organisms like plants and animals play a role in the water cycle.

• Only about 3% of Earth’s water is fresh, and most is frozen.

• Surface water is found in rivers and lakes, organized within watersheds.

• Groundwater is stored in underground layers called aquifers.

• The ocean is a vast body of salt water with diverse floor features.

Poll

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