Water on Earth

Water on Earth

Middle School

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Learning Objectives

• Describe what water is and identify where it is found on Earth.

• Provide an overview of the stages that make up the Earth's water cycle.

• Explain the ocean's integral role in the water cycle and its connection to reservoirs.

Key Vocabulary

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Evaporation

The process of liquid water changing into water vapor gas due to solar heat.

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Condensation

The process of water vapor gas cooling and changing back into liquid water droplets.

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Precipitation

Water that falls from clouds to Earth's surface as rain, snow, sleet, or hail.

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Transpiration

The release of water vapor from plant leaves into the atmosphere.

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Runoff

Precipitation that flows over the land's surface into various bodies of water.

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Infiltration

The process by which water on the ground surface soaks down into the soil.

What is Water and Where is it Found?

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What is Water?

• ​Water is a chemical compound with the formula H₂O.

• ​​It consists of two hydrogen atoms and one oxygen atom.

• ​It exists on our planet as a solid, liquid, or gas.

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The Hydrosphere

• ​The hydrosphere is made up of all water on the Earth.

• ​​Our Earth is often called the "water planet" for this reason.

• ​Water covers about 71 percent of the total Earth's surface.

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Types of Water

• ​About 97 percent of all of Earth's water is saltwater.

• ​​This type of water is not suitable for people to drink.

• ​Only about 3 percent is freshwater, which supports life on land.

Multiple Choice

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

• Most of Earth's water is freshwater, and a small fraction is saltwater.

• Earth's water is equally divided between saltwater and freshwater.

• About 97% of Earth's water is saltwater, while only 3% is freshwater.

• Water only exists in a liquid state on Earth's surface.

Earth's Freshwater Distribution

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Ice Caps and Glaciers

• ​Most of Earth's freshwater, 68.7%, is frozen solid in ice.

• ​​This water is locked away in large glaciers and polar ice caps.

• ​It is not easily available for us to use for our needs.

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Underground Water

• ​About 30.1% of all freshwater on Earth is found underground.

• ​​This groundwater is stored within layers of soil, sand, and rock.

• ​We can access this water through natural springs or by digging wells.

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Surface Water

• ​Only 1.2% of all freshwater is easily accessible surface water.

• ​​This water is found in our planet's lakes, rivers, and swamps.

• ​It supports many ecosystems and is our main source for drinking water.

Multiple Choice

According to the slide, where is the largest portion of Earth's freshwater located?

• In underground aquifers.

• In the atmosphere as water vapor.

• In surface rivers and lakes.

• In ice caps and glaciers.

The Water Cycle

• The water cycle is the continuous movement of Earth's water.

• The sun's energy powers the entire water cycle.

• Oceans drive much of the water cycle, providing most of the evaporation that later returns to Earth as precipitation.

Multiple Choice

What is the primary energy source that powers the water cycle?

• Wind patterns moving across the ocean.

• The Earth's geothermal heat.

• Energy from the Sun.

• The gravitational pull of the moon.

Processes of the Water Cycle

• The sun heats water, turning it into water vapor.

• This water vapor rises, cools, and forms clouds.

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

Multiple Choice

What happens during the process of condensation in the water cycle?

• Liquid water turns into water vapor and rises.

• Water falls from the clouds as rain or snow.

• Water vapor cools and changes into liquid water droplets to form clouds.

• Plants release water vapor from their leaves.

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Common Misconceptions

Misconception	Correction
Earth is constantly creating new water.	The amount of water on Earth is finite and is continuously recycled.
Most usable freshwater is in rivers and lakes.	Most usable freshwater is frozen in glaciers or is underground as groundwater.
Drinking salt water is safe in an emergency.	Drinking salt water causes dehydration and is dangerous for the human body.
The water cycle has a distinct start and end.	The water cycle is a continuous global process with no true beginning or end.

Multiple Choice

How does the role of the ocean in the water cycle compare between the processes of evaporation and precipitation?

• The ocean is a major source for evaporation and also receives the majority of Earth's precipitation.

• The ocean is the primary source for evaporation but receives only a small amount of precipitation.

• The ocean only cools the air for precipitation and plays no role in evaporation.

• The ocean only collects runoff and is not directly involved in atmospheric evaporation or precipitation.

Multiple Choice

If a community relies heavily on surface water like rivers for its needs, what does this imply about their direct usage of Earth's total freshwater resources?

• They are using a very small fraction (around 1.2%) of Earth's total freshwater.

• They are using the largest available source of freshwater.

• They have direct access to the 30.1% of freshwater stored as groundwater.

• They are mainly using melted water from glaciers and ice caps.

Multiple Choice

Where is about 30% of Earth’s freshwater found?

• In rivers and lakes on the surface

• Underground within layers of soil, sand, and rock

• Frozen in glaciers and ice caps

• In the atmosphere as water vapor

Multiple Choice

If rising global temperatures were to cause significant melting of the Greenland and Antarctic ice sheets, what would be the most significant immediate consequence for the global water distribution?

• A large volume of water would move from being stored as ice to becoming part of the ocean, causing sea levels to rise.

• The percentage of freshwater would increase significantly compared to saltwater.

• The total amount of water on Earth would decrease due to evaporation.

• The amount of groundwater would decrease as it is all drawn to the surface.

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Summary

• Water covers 71% of Earth's surface, but only 3% of it is freshwater.

• Most freshwater is frozen in glaciers or stored underground as groundwater.

• The water cycle is the sun-powered process that continuously recycles Earth’s water.

• Key processes include evaporation, condensation, precipitation, runoff, and infiltration.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

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• 4