The Hydrosphere

The Hydrosphere

Middle School

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Learning Objectives

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

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

• Describe the distribution of fresh and salt water on Earth in various storage systems.

• Recognize the role of living organisms in processes like 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 a liquid heats up and transforms into a gas, also known as water vapor.

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Transpiration

The process where plants absorb water through their roots and then give off water vapor from their leaves.

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Condensation

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

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Crystallization

The process by which water vapor in the atmosphere freezes directly into ice crystals, forming snow.

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Precipitation

Water falling to Earth from the atmosphere in the form of rain, snow, hail, or sleet.

Key Vocabulary

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Gravity

Gravity is the invisible force that pulls matter, or anything with mass, downward toward the Earth's center.

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Energy Transfer

Energy transfer describes the movement of energy from one object or system of objects to another.

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Decomposition

Decomposition is the natural process of breaking down dead organic organisms, which releases water and nutrients.

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Watershed

A watershed is the specific land area that channels and supplies rainwater and snowmelt to a river.

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Aquifer

An aquifer is a large underground layer of water-bearing permeable rock or sediment that holds valuable groundwater.

The Water Cycle

• The sun’s heat turns liquid water into a gas called water vapor.

• Water vapor cools and turns into liquid droplets, forming clouds.

• Water falls back to Earth as rain, snow, hail, or sleet.

Multiple Choice

What happens to liquid water when it is heated by the sun?

• It turns into a gas called water vapor.

• It forms clouds immediately.

• It falls back to Earth as rain.

• It becomes cooler.

Multiple Choice

What is the relationship between water vapor and the formation of clouds?

• Clouds form when water vapor cools and turns into liquid droplets.

• Clouds are made of water vapor that is heated by the sun.

• Clouds form at the same time that rain begins to fall.

• Water vapor is another name for a cloud.

Multiple Choice

If the air in the atmosphere never cooled, what would be the most likely consequence for the water cycle?

• Clouds would not form, and it would not rain.

• More water vapor would be created by the sun.

• Water would immediately fall as rain without forming clouds.

• The sun's heat would no longer turn water into a gas.

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Driving Forces of the Water Cycle

Solar Energy

• The sun's energy warms water on the Earth's surface, providing the energy needed for evaporation.

• This energy transfer is the main engine that powers the entire water cycle on Earth.

• It drives water movement from oceans, land, and even plants into the atmosphere.

Gravity

• Gravity causes precipitation, such as rain, snow, or hail, to fall from clouds.

• It drives the downhill movement of water across the land through rivers, streams, and glaciers.

• This force helps transport water back toward lakes, oceans, and other bodies of water, completing the water cycle.

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

Multiple Choice

What is the specific role of solar energy in the water cycle?

• It provides the energy that causes water to evaporate.

• It pulls water down from the clouds as precipitation.

• It causes the downhill flow of water in rivers.

• It helps move water back towards the oceans.

Multiple Choice

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

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

• Water would evaporate much faster from oceans and lakes.

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

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

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Role of Living Organisms

Transpiration in Plants

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

• ​​They then release this water as vapor into the atmosphere.

• ​This process occurs through tiny pores located on their leaves.

Respiration & Decomposition

• ​Animals take in water and release some back through respiration, or breathing.

• ​​When plants and animals die, their bodies start to decompose.

• ​Decomposition releases the stored water back into the soil and the atmosphere.

Multiple Choice

What is the primary role of living organisms like plants and animals in the water cycle?

• By creating water from sunlight and air.

• By storing water in their bodies permanently.

• By releasing water through processes like transpiration, respiration, and decomposition.

• By causing water to evaporate from oceans and lakes.

Multiple Choice

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

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

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

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

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

Multiple Choice

If a forest fire eliminated all the plants and animals in an area, what would be the most likely immediate impact on the local water cycle?

• The amount of water returned to the soil and atmosphere would significantly decrease.

• The amount of water in the soil would increase because it is not being used.

• The amount of water vapor in the atmosphere would increase.

• The water cycle would stop completely and permanently.

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Distribution of Earth's Water

• Roughly 97% of Earth's water is salt water, found in our oceans.

• ​Only about 3% of the water on the entire planet is fresh water.

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

• The remaining fresh water is mostly groundwater found deep under the ground.

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Multiple Choice

Which statement accurately describes the overall distribution of water on Earth?

• Most of it is salt water found in oceans.

• It is evenly divided between fresh and salt water.

• Most of it is fresh water found in glaciers.

• It is mostly found as groundwater deep underground.

Multiple Choice

What is the state and location of the majority of Earth's fresh water?

• It is found in the oceans.

• It exists as groundwater.

• It is frozen in glaciers and ice sheets.

• It is evenly split between ice and groundwater.

Multiple Choice

Based on the data, what is the strongest reason why usable water is a limited resource?

• Because salt water is becoming more common than fresh water.

• Because glaciers and ice sheets are melting too quickly.

• Because groundwater is the largest source of water on the planet.

• Because only a very small fraction of Earth's water is accessible fresh water.

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Surface Water Systems

Rivers and Watersheds

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

• The land area supplying water to a river system is known as a watershed, which is a critical resource.

• Watersheds are separated from one another by a high ridge of land which is referred to as a divide.

Ponds and Lakes

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

• They are an important storage component for fresh water as part of the overall global water cycle.

Multiple Choice

What is the correct term for the land area that supplies water to a river system through a main river and its tributaries?

• A watershed

• A divide

• A pond

• A tributary

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 is found in low-lying areas, while a lake is on a ridge.

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

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

Multiple Choice

If a high ridge of land sits between two separate river systems, what is its role?

• The ridge acts as a divide, separating the water flow into two different watersheds.

• The ridge is the main source of fresh water for both river systems.

• The ridge is a low-lying area where a lake will eventually form.

• The ridge helps to combine the two river systems into a single, larger one.

Groundwater Systems

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

• Water seeps through an unsaturated zone to a saturated zone below.

• Aquifers are underground layers that store water, accessed by wells.

Multiple Choice

What is groundwater?

• Fresh water stored in underground soil and rock layers

• Salt water found in deep ocean trenches

• Water vapor condensed in the atmosphere

• Frozen water located in glaciers and ice caps

Multiple Choice

What is the relationship between the unsaturated zone and the saturated zone?

• Water seeps down through the unsaturated zone to collect in the saturated zone.

• Water evaporates from the saturated zone to form the unsaturated zone.

• The unsaturated zone filters water for the saturated zone.

• The saturated zone is located above the unsaturated zone.

Multiple Choice

Based on the way groundwater systems are structured, why must a well be drilled to a significant depth to be effective?

• The well must reach the aquifer where groundwater is stored.

• The well only needs to enter the top layer of soil.

• The well will work as long as it is in the unsaturated zone.

• The well must be connected to a river or lake.

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Ocean Characteristics and Features

• Salinity is the amount of dissolved salts, which makes seawater dense.

• 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 features include seamounts, trenches, and mid-ocean 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

Multiple Choice

Why does water pressure increase as ocean depth increases?

• Because the water gets colder with depth

• Because of the increasing weight of the water above

• Because the salt content becomes much higher

• Because of the movement of ocean currents

Multiple Choice

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

• Low pressure and warm water

• High pressure and cold water

• High pressure and warm water

• Low pressure and cold water

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Common Misconceptions

Misconception	Correction
Most of Earth's water is fresh and usable.	97% is salt water; most fresh water is locked in glaciers.
The water cycle is a single, simple loop.	The water cycle has multiple pathways and storage areas.
Groundwater exists in underground rivers.	Groundwater is held in aquifers, which are layers of rock and soil.
The ocean floor is a flat, sandy basin.	The ocean floor has mountains, deep trenches, and underwater volcanoes.

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Summary

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

• Water moves through evaporation, condensation, and precipitation, with organisms also playing a role.

• Only 3% of Earth's water is fresh, located in glaciers, groundwater, rivers, and lakes.

• The ocean is a vast body of saltwater with a varied floor and conditions.

Poll

On a scale of 1-4, how confident are you about describing the water cycle and its driving forces?

• 1 (Not confident)

• 2 (A little confident)

• 3 (Mostly confident)

• 4 (Very confident)