Grade by Grade
E. Earth and Space Systems · Soils in the Environment

How People Change Soil

E1.2 E1.1 A1.1 A1.4 A3.1About 45 minutes
Learning goals
  • I can describe ways human activities harm soil.
  • I can describe ways people can improve soil or prevent harm.
  • I can assess an activity by thinking about its good and bad effects.
  • I can research a real Ontario example of people healing soil.

Words to know

human activity
Something people do, like building, farming, driving or mining.
impact
The effect that something has. An impact can be good or bad.
compaction
When soil is pressed down hard, so the air spaces are squeezed out.
pave
To cover the ground with a hard surface like asphalt or concrete.
restore
To bring something back to a healthy state.
perspective
The way one person or group sees something.

A field becomes a neighbourhood

For 100 years, a field at the edge of town grew corn. This year, big machines arrived. They scraped away the plants, dug holes and poured concrete. Soon there will be houses, a road and a parking lot.

New homes are important. Families need places to live! But what happens to the soil? Today you will look at the impact of human activities on soil, the bad and the good.

A yellow bulldozer pushing soil on a cleared field beside a cornfield, with new houses being built in the distance.
The bulldozer is scraping away farm soil to make room for new houses. Heavy machines also squeeze, or compact, the soil. AI-generated image

Ways people can harm soil

  • Paving and building. When soil is covered with roads, parking lots and buildings, rain can't soak in, plants can't grow, and soil animals lose their homes. Some of Ontario's best farm soil has been covered by cities and roads, and it can't easily be made again.
  • Compaction. Heavy machines, cars and lots of feet squeeze soil. The air spaces are crushed. Roots and worms can't move, and water puddles or runs off.
  • Removing plants and trees. Bare soil erodes in wind and rain.
  • Pollution. Spills, chemicals, too much road salt and litter harm soil life (last lesson).
  • Farming without care. Growing the same crop every year and leaving fields bare can use up nutrients and let soil erode.
  • Mining and some factories. Digging can remove soil, and some smoke and waste can pollute the land.
LOOSE SOILCOMPACTED SOILwater soaks in through the spacessqueezed tight: water puddleson top or runs offpuddle
Compaction. Loose soil has spaces for air, water and roots. Squeezed soil has no spaces, so water puddles or runs off.

Ways people can help soil

  • Plant trees, grass, gardens and cover crops, so soil is never bare for long.
  • Add compost, manure and mulch to build humus.
  • Stay on paths and keep heavy machines off wet soil to prevent compaction.
  • Use less road salt, and never dump chemicals.
  • Pick up litter.
  • Build in smart ways: keep trees, make rain gardens, and use paving stones that let water soak through.
  • Restore damaged land, like the people of Sudbury did!

A true Ontario story: Sudbury's regreening

Sudbury, in northern Ontario, has many mines. For many years, smoke from the plants that melted metal out of rock (called smelters) put harmful gases into the air. The polluted rain made the soil very sour (acidic), and the smoke harmed plants. Trees were cut for wood and fuel, and without plants, rain eroded the soil. Large areas of land became bare, dark rock with almost no plants.

Then people worked together to fix it. The smelters were changed to put out much less pollution. Starting in 1978, workers, students and volunteers spread crushed limestone (lime) to make the soil less sour, added fertilizer, planted grass seed, and planted millions of trees. Slowly, plants came back, then insects, birds and animals. Today, much of the land around Sudbury is green again. It is still being restored.

This shows that people can harm soil, but people can also heal it.

Before:bare, sour soilFrom 1978:spread crushed limePlant grass andmillions of treesToday:much of it is green
Sudbury's regreening, step by step. People healed the soil by making it less sour and planting grass and trees.
Worked example

Let's assess an activity

A town wants to turn part of a park into a parking lot for the new arena. Assess the impact on soil.

  1. Good for people: More parking for families going to hockey games and skating.
  2. Harm to soil: Pavement covers the soil. Rain can't soak in, so more runoff goes into storm drains. Soil animals lose their home. Trees may be cut down.
  3. Think about other perspectives: Families who play in the park would lose space. Neighbours might get more flooding.
  4. How to make it better: Make the lot smaller, keep the big trees, use paving stones that let water soak in, add a rain garden at the edge, or encourage walking, biking and buses so fewer spaces are needed.

The parking lot helps people park, but it harms the soil under it. If it is built, the town can lessen the harm with smart choices.

ActivityImpact on soilHow to lessen or prevent harm
building housescovers and compacts soilkeep trees, cover bare soil during building, plant gardens after
walking off pathscompacts soil, wears away plantsstay on trails
salting sidewalkssalt harms roots and soil lifeuse only as much as needed; shovel first
leaving fields bare in winterwind and snowmelt erode soilplant cover crops
miningremoves soil, can pollutecontrol pollution, restore land with lime, plants and trees
Human activities: impacts and solutions
Worked example

Let's research Sudbury's regreening

Jacob wants to tell his class how people healed the land around Sudbury. How can he research it?

  1. Ask a question: How did people bring plants back to the land around Sudbury?
  2. Find information: With his mom, he reads a library book and a website from the City of Greater Sudbury or a science centre. He checks that the sources are reliable (from experts, not just anyone).
  3. Take notes: soil was very sour; people spread crushed limestone; planted grass and millions of trees; started in 1978.
  4. Share: He makes a before-and-after poster with labels.

Jacob used a research process: ask, find reliable information, take notes, share.

Just for fun

What did the earthworm say about paving stones that let rain soak through?

"Finally, a sidewalk with holes in all the right places!"

Hands-on activity

Compaction test

You need: 2 plastic cups with the bottoms cut off (a grown-up cuts them), a measuring cup, water, a timer, and a grown-up helper.

  1. Pick two spots: a garden bed (soft soil) and a well-walked path or a spot where cars park (packed soil). Ask a grown-up first.
  2. At each spot, push a cup about 2 cm into the soil, cut end down.
  3. Pour 250 mL of water into the cup. Time how long it takes for all the water to soak in. Stop at 10 minutes if it hasn't soaked in.
  4. Record your results in a table.
  5. Which soil soaked up water faster? Which one is compacted? What would happen to rain on that soil?
  6. Think of one way to protect soil from compaction at your home or school.

Safety: Stay away from roads and parking lots with moving cars. Wash your hands after.

Your turn

1

Name two human activities that can harm soil.

2

What is compaction?

3

Name two ways people can help soil.

4

What made the soil around Sudbury so sour?

5

What did people spread on Sudbury's soil to make it less sour?

6

Why can't rain soak into a parking lot?

7

What does restore mean?

More practice: warm-up

1

True or false: People can only harm soil, never help it.

2

Name one machine that can compact soil.

3

Does staying on the trail in a park help or harm the soil?

4

What does impact mean?

5

In which part of Ontario is Sudbury?

More practice: on your own

1

Why is it a problem when good farm soil is paved over?

2

In a compaction test, water took 1 minute to soak into a garden bed and 9 minutes on a path. Which soil is compacted? How much longer did it take?

3

Explain how cutting down trees can lead to erosion.

4

A builder must clear a lot to build a house. Name two ways to protect the soil.

5

What are two steps of a research process?

Challenge

1

A new road will help people get to the hospital faster, but it will cover a farm field. Assess: what is good, what is harmful, and one way to lessen the harm.

2

How does the Sudbury story show that people can both harm and help soil?

3

Why do you think it took many years, not just one summer, to regreen Sudbury?

Check your understanding

Quiz

1.

Which activity compacts soil?

2.

What happens to rain on a paved parking lot?

3.

Which is a way to help soil?

4.

People in Sudbury spread crushed limestone to...

5.

To assess an activity's impact on soil, you should think about...

6.

A rain garden helps because it...

For parents and teachers

Big idea (E1.2): Human activity can harm soil (sealing by pavement and buildings, compaction, loss of plant cover, pollution, poor farming practices, mining) and humans can improve soil or lessen harm (planting, organic matter, avoiding compaction, smart development, restoration). The Sudbury regreening program (since 1978: liming acidic soils, fertilizing, seeding grasses and planting millions of trees, plus large reductions in smelter emissions) is a real Ontario example of restoration.

How to help: Practise assessing with "good for people / harm to soil / how to make it better". Support research with reliable sources (A1.1) such as library books and municipal or science centre websites. Look at your own neighbourhood: where is soil paved, compacted or protected (A3.1)?

Common difficulties:

  • All-or-nothing thinking ("building is bad"). Encourage balance: people need homes and roads; the goal is to lessen harm.
  • Not seeing compaction as harm. The compaction test makes it concrete.

Safety (A1.4): Adults cut cups. Do the compaction test away from traffic.