Water on Earth's Surface

Water on Earth's Surface

Middle School

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Learning Objectives

• Describe the water cycle as a continuous process driven by the sun and gravity.

• Explain how gravity drives the downhill movement of water on and below Earth’s surface.

• Identify Earth's major water reservoirs, including oceans, ice, groundwater, and living things.

• Explain how Earth’s processes result in the uneven distribution of our limited freshwater.

Key Vocabulary

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Water Cycle

The continuous movement of water on, above, and below the Earth’s surface is the water cycle.

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Evaporation

Evaporation is when the Sun's energy turns liquid water on Earth into water vapor, a gas.

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Condensation

Condensation is water vapor in the air cooling and changing back into liquid water, forming clouds.

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Precipitation

Precipitation is water falling from clouds as rain, snow, sleet, or hail due to gravity.

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Transpiration

Transpiration is the process where plants release water vapor from their leaves into the surrounding air.

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Deposition

The process in which water vapor in the air changes directly into ice without first becoming liquid, such as when frost forms.

Key Vocabulary

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Gravity

The force that pulls water downward, driving its flow on and below the surface.

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Reservoir

A location where water is stored, such as an ocean, glacier, or lake.

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Groundwater

Water held in the soil and in pores and fractures of rock.

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Aquifer

An underground layer of rock or sediment that holds groundwater.

The Water Cycle: Driven by Sun and Gravity

• The sun's energy drives evaporation, turning liquid water into water vapor.

• Water vapor rises, cools, and condenses to form clouds.

• Gravity pulls water back to Earth as precipitation like rain or snow.

Multiple Choice

What are the two main forces that drive the water cycle?

• The sun's energy and Earth's gravity

• The moon's pull and ocean currents

• Wind patterns and Earth's rotation

• Cloud formation and volcanic activity

Multiple Choice

What is the relationship between the sun's energy and the formation of clouds?

• It causes water to evaporate, rise, and then condense into clouds.

• It pulls water from the clouds back to the ground as rain.

• It pushes the clouds around the Earth, creating wind.

• It freezes water vapor directly into snow and ice.

Multiple Choice

If the sun's energy caused clouds to form, but then the force of gravity disappeared, what would most likely happen?

• The water droplets would remain in the clouds.

• The clouds would immediately turn into ice.

• The rain would fall much faster than usual.

• The sun's energy would pull the water back down.

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The Role of Living Organisms

• Living organisms, especially plants, are a vital part of the water cycle.

• Plants release water vapor from their leaves in a process called transpiration.

• When organisms decompose, water is released back into the environment.

Multiple Choice

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

• They play a key part in moving water between the land and the atmosphere.

• They convert sunlight directly into water.

• They prevent water from ever leaving the soil.

• They only take in water but do not release it.

Multiple Choice

How do plants contribute to the movement of water from the ground to the atmosphere?

• By absorbing water through their roots and then releasing it as vapor from their leaves.

• By catching rainwater on their leaves and letting it drip to the ground.

• By releasing stored water only when they decompose.

• By changing the temperature of the soil to cause evaporation.

Multiple Choice

If a large number of trees were removed from an area, what would be the most likely effect on the local water cycle?

• The amount of water vapor released into the air from plants would significantly decrease.

• The amount of water released by decomposition would immediately increase.

• More water would be absorbed from the soil by the remaining organisms.

• The water cycle in the area would stop completely.

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Surface Water Movement

• When precipitation falls on land, it becomes surface water that gathers in streams.

• ​These small streams then begin to flow into much larger rivers.

• Gravity pulls the surface water, causing it to continuously flow downhill over landforms.

• Most rivers eventually flow back into the ocean, the largest water reservoir.

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Multiple Choice

What is the primary force that causes surface water to flow continuously downhill over landforms?

• The force of gravity pulling it downwards

• The heat from the sun causing it to evaporate

• The wind pushing it across the land

• The rotation of the Earth spinning the water

Multiple Choice

Which statement best describes the relationship between streams and rivers as surface water moves across land?

• Small streams gather together to form larger rivers.

• Large rivers break apart to form smaller streams.

• Streams and rivers are separate and do not connect.

• Rivers flow into streams before reaching the ocean.

Multiple Choice

Imagine a dam is built across a large river, blocking its path. Based on the principles of surface water movement, what is the most likely outcome?

• The river water would likely build up behind the dam, forming a lake.

• The river would start to flow uphill to get around the dam.

• The water from the river would immediately soak into the ground.

• The ocean would push water back to destroy the dam.

Groundwater and Aquifers

• Groundwater is water that exists underground in soil and rock.

• An aquifer is an underground layer of rock that holds groundwater.

• Groundwater can flow underground and seep into rivers and lakes.

Multiple Choice

What is groundwater?

• Water that is found underground in soil and rock

• Water that flows on the surface in rivers

• Water that is frozen in glaciers

• Water that is stored in the atmosphere

Multiple Choice

What is the relationship between an aquifer and groundwater?

• An aquifer is an underground layer of rock that holds groundwater.

• Groundwater is a type of rock that holds water.

• An aquifer is a large, man-made underground tank.

• Groundwater seeps into the ground to create aquifers.

Multiple Choice

If a large amount of pollution soaks into the ground, what could be a possible effect on a nearby lake?

• The groundwater could flow into the lake, carrying pollution with it.

• The pollution would be trapped in the aquifer and not move.

• The lake water would seep into the ground and clean the pollution.

• The pollution would stay on the surface and not enter the groundwater.

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Uneven Distribution of Groundwater

• Freshwater resources like groundwater are distributed unevenly across our planet.

• Some regions have abundant aquifers, while other regions have very few.

• This is due to rock type, geological history, and long-term climate patterns.

• This makes fresh water a limited resource that we need to conserve.

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Multiple Choice

Which statement best describes the distribution of groundwater on Earth?

• It is spread out perfectly evenly across the planet.

• It is found in some regions more than in others.

• It exists in equal amounts in all types of rock.

• It is most abundant in the Earth's polar regions.

Multiple Choice

What causes some regions to have large amounts of groundwater while others have very little?

• The number of people and cities in the region.

• The region's climate, rock type, and geological history.

• The number of rivers and oceans near the region.

• The types of plants and animals living in the region.

Multiple Choice

A region has a dry climate and rock types that do not hold water well. What conclusion can be drawn about the water supply in this region?

• The area will likely have an unlimited supply of fresh water.

• Fresh water is a limited resource that must be managed carefully.

• The rock type will not affect the amount of available water.

• Long-term climate patterns do not impact water availability.

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Glaciers and Ice Sheets

• Water is stored in reservoirs, the largest one being the ocean.

• Glaciers and ice sheets are vast bodies of frozen water.

• The weight of accumulating snow compresses lower layers into a solid ice mass.

• Gravity causes this massive sheet of ice to flow slowly downhill.

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Multiple Choice

What are glaciers and ice sheets?

• Vast bodies of frozen water

• Large rivers of flowing saltwater

• Underground lakes of fresh water

• Dense clouds of ice crystals

Multiple Choice

What is the relationship between snowfall and the formation of a glacier?

• The weight of accumulating snow compresses lower layers into ice.

• Melting snow freezes into a solid sheet of ice overnight.

• Glaciers are formed by frozen ocean water.

• Light, fluffy snow is what causes glaciers to flow downhill.

Multiple Choice

What would most likely happen to a glacier if the force of gravity on Earth became much stronger?

• The glacier would begin to flow downhill more quickly.

• The glacier would melt and turn into a river.

• The glacier would stop moving altogether.

• The snow on top would become lighter and fluffier.

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Climate Change and the Water Cycle

• Warmer global temperatures cause more water to evaporate from oceans and land.

• This extra moisture can lead to heavier rain and storms, causing floods.

• In other areas, warmer temperatures can dry out the land, causing droughts.

• Scientists study these changes using computer models and global precipitation data.

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Multiple Choice

What is the first step in how climate change affects the water cycle?

• Warmer temperatures cause more water to evaporate.

• Colder temperatures cause water to freeze.

• Increased rainfall causes oceans to cool down.

• Scientists use computer models to change the weather.

Multiple Choice

What is the relationship between increased water evaporation and weather patterns?

• It can lead to more extreme weather, like heavy storms or droughts.

• It only causes more rain in every part of the world.

• It makes the climate drier everywhere.

• It has no significant effect on weather patterns.

Multiple Choice

If scientists use computer models to analyze an increase in global precipitation data, what conclusion are they most likely to draw?

• That warmer global temperatures are causing changes in the water cycle.

• That the Earth's oceans are shrinking in size.

• That all areas of the world are becoming wetter.

• That computer models are the only way to prevent floods.

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Common Misconceptions

Misconception	Correction
The total amount of water on Earth changes.	Earth's water amount is constant; it just moves and changes state.
Plants destroy water.	Plants move water from the ground to the air through transpiration.
Groundwater is like an underground river.	Groundwater is held in tiny spaces in soil and rock, like a sponge.
Glaciers are stationary and do not move.	Glaciers are large masses of ice that flow slowly downhill.
Water only flows on the surface.	Water flows on the surface in rivers and also underground.

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Summary

• The sun's energy and gravity power the water cycle's key processes.

• Water is stored in many places, like oceans, ice, and underground.

• The uneven distribution of groundwater makes fresh water a limited resource.

• Changes in climate can affect the water cycle, causing floods and droughts.

Poll

On a scale of 1-4, how confident are you about explaining the movement of water through Earth's systems?

• 1

• 2

• 3

• 4