B. Biology: Sustainable Ecosystems and Climate Change · Sustainable Ecosystems and Climate Change

Earth's Four Spheres and How They Interact

B2.1 A1.1 A1.2About 65 minutes

Learning goals

I can name and describe the biosphere, hydrosphere, lithosphere and atmosphere.
I can give examples of matter and energy moving between the spheres.
I can explain why interactions between the spheres are important for ecosystem sustainability.
I can trace how a change in one sphere spreads to the others.

Words to know

biosphere
All the parts of Earth where life exists, plus all living things: plants, animals, fungi, microorganisms and people.

hydrosphere
All of Earth's water: oceans, lakes, rivers, groundwater, ice, snow and water vapour.

lithosphere
Earth's solid, rocky outer layer, including the crust, the rocky upper mantle, and the soil and sediments on top.

atmosphere
The layer of gases surrounding Earth, mostly nitrogen (about 78%) and oxygen (about 21%).

ecosystem
All the living things in an area plus the non-living (abiotic) parts they interact with, such as water, soil, air and sunlight.

sustainability
The ability of an ecosystem to keep functioning and supporting life over a long time without running down.

interaction
Any way two things affect each other; here, any exchange of matter or energy between spheres.

Remember from Grade 7

In Grade 7 you learned that an ecosystem is a network of interactions between biotic (living) and abiotic (non-living) parts, and you met the word biosphere. You also traced energy through food chains and followed the water, carbon and nitrogen cycles. This Grade 9 unit goes deeper. You will see ecosystems as part of one connected Earth system, explain how matter cycles and energy flows, and use that understanding to make sense of climate change and what people are doing about it.

Let's start with a winter morning

It is January at a lake near Huntsville. You breathe out, and a little cloud appears. The sun rises over a frozen lake, a chickadee flits between spruce trees, and wind blows loose snow across the ice.

In that one moment, all four of Earth's spheres are interacting:

Your breath (biosphere) adds water vapour and carbon dioxide to the air (atmosphere).
The ice and snow (hydrosphere) sit on rock and soil (lithosphere).
The spruce trees (biosphere) take carbon dioxide from the air and water from the soil.
The wind (atmosphere) moves snow (hydrosphere) around.

Scientists call Earth a system: a set of parts that affect each other. To understand ecosystems, and climate change, you have to look at the whole system.

The four spheres

Atmosphere: the blanket of gases around Earth. It is about 78% nitrogen, 21% oxygen, almost 1% argon, and tiny amounts of other gases, including carbon dioxide (about 0.04%) and water vapour. It holds heat near the surface, carries weather, and shields life from much of the Sun's ultraviolet light.
Hydrosphere: all water on Earth in all three states. About 97% is salty ocean water. Most of Earth's fresh water is frozen in ice sheets and glaciers or stored underground (you studied this in Grade 8 Water Systems).
Lithosphere: the solid, rocky outer shell of Earth: the crust and the very top of the mantle, plus the soil and sediments on top. It supplies minerals and nutrients such as phosphorus, calcium and potassium.
Biosphere: every living thing, and every place where life is found: from the deep ocean, through soil, to the lower atmosphere where birds, insects and pollen travel.

The spheres overlap. Soil is a mix of all four: rock particles (lithosphere), water, air and living things like bacteria, fungi and worms.

The four spheres of Earth and a few of the ways matter and energy move between them. Every arrow is an interaction. Change one sphere and the others change too.

Interactions: matter and energy on the move

An interaction happens whenever matter (atoms and molecules) or energy moves from one sphere to another. Some interactions are fast (you breathe out in a second). Others are very slow (rock weathering into soil can take thousands of years). The table shows some of the most important ones.

Interaction	What moves	Why it matters
Photosynthesis (biosphere ↔ atmosphere)	Carbon dioxide into plants; oxygen out	Makes food for almost every ecosystem and adds the oxygen we breathe
Cellular respiration (biosphere → atmosphere)	Carbon dioxide and water vapour out of living things	Releases the energy organisms need to live
Evaporation and precipitation (hydrosphere ↔ atmosphere)	Water	Delivers fresh water to land ecosystems
Weathering and erosion (hydrosphere and atmosphere → lithosphere)	Rock broken down and moved by water, ice and wind	Forms soil and releases minerals that plants need
Roots and decomposers (biosphere ↔ lithosphere)	Nutrients taken up from soil; dead matter returned to soil	Keeps nutrients cycling so soil stays fertile
Volcanic eruptions (lithosphere → atmosphere)	Gases such as carbon dioxide and sulfur dioxide, plus ash	Can change climate for a year or two after a big eruption
Ocean–air exchange (hydrosphere ↔ atmosphere)	Carbon dioxide dissolves in or leaves seawater; heat moves between ocean and air	The ocean absorbs a large share of extra CO₂ and heat

Some key interactions between Earth's spheres. Each one moves matter, energy, or both.

A lake in Ontario's Canadian Shield holds all four spheres in one place. The trees and fish are part of the biosphere; the sun's energy drives the whole system (not to scale).

Why interactions matter for sustainability

An ecosystem is sustainable when it can keep supporting life year after year. That only works because the spheres keep trading matter and energy:

Matter is recycled. Earth gets almost no new matter from space, so the same carbon, nitrogen, water and phosphorus atoms must be used over and over. The cycles move these atoms between spheres.
Energy keeps flowing. Sunlight (energy from outside Earth) enters the atmosphere, is captured by plants in the biosphere, and eventually leaves Earth as heat. Ecosystems need a constant supply of new energy.
Conditions stay in range. Interactions keep temperature, water supply and the makeup of the air within a range that living things can tolerate.

When people change one sphere quickly, for example by adding carbon dioxide to the atmosphere or paving over soil, the effects ripple through the other spheres. Much of this unit is about those ripples.

Think like a systems scientist

When you study any environmental change, ask three questions:

Which sphere changed first?
What matter or energy is moving differently now?
Which other spheres are affected, and how?

This habit will help you in every lesson, and in Grade 10 Science and Geography too.

Worked example

Let's trace a forest fire through the spheres

A lightning strike starts a wildfire in a boreal forest in northern Ontario. Trace how this change in one sphere affects the other three.

Start: lightning (energy in the atmosphere) ignites trees (biosphere).
Biosphere → atmosphere: burning releases carbon dioxide, water vapour, smoke and soot into the air. Smoke can lower air quality hundreds of kilometres away.
Biosphere → lithosphere: ash adds minerals to the soil, but without plant roots, the soil is easier to erode.
Lithosphere → hydrosphere: heavy rain after the fire can wash soil and ash into streams, making the water cloudy (more turbid) and adding nutrients.
Back to the biosphere: over the following years, new plants grow in the sunny, mineral-rich soil (you will study this as succession in Lesson 8).

One fire touches all four spheres: gases and soot to the atmosphere, ash and erosion in the lithosphere, sediment in the hydrosphere, and a reset of the living community in the biosphere.

Worked example

Let's classify interactions

For each event, name the two spheres involved and what moves: (a) a maple tree's roots take up water; (b) rain dissolves limestone; (c) a moose breathes out.

(a) Water moves from the soil (lithosphere/hydrosphere) into the tree (biosphere). Water in soil is part of the hydrosphere, held in the lithosphere.
(b) Rain (hydrosphere, with a little dissolved CO₂ from the atmosphere) dissolves rock (lithosphere); minerals move into the water.
(c) Carbon dioxide and water vapour move from the moose (biosphere) to the air (atmosphere).

(a) hydrosphere/lithosphere → biosphere: water; (b) hydrosphere and lithosphere: water dissolves rock, so minerals move from the rock into the water; (c) biosphere → atmosphere: CO₂ and water vapour.

Hands-on activity

Build a sealed ecosystem jar (A1.2)

You need: a clean, clear glass jar with a lid (a large pickle or mason jar), small pebbles or gravel, potting soil, a few small plants or moss from a garden centre or your yard (ask permission), a spray bottle of water, a notebook.

Put 2 to 3 cm of pebbles in the bottom, then 5 to 8 cm of soil on top.
Plant the moss or small plants. Mist them with water until the soil is damp but not soggy.
Close the lid. Place the jar in bright light but not direct hot sun.
Label each of the four spheres on a sketch of your jar.
Observe every day for two weeks. Record: water droplets on the glass, plant growth, any mould, the colour of the plants.
Analyse: Where does the water on the glass come from, and where does it go? Where do the plants get carbon dioxide inside a closed jar? (Hint: soil microbes and the plants themselves carry out cellular respiration.)
Communicate: write 4 to 6 sentences explaining which interactions keep your jar going, and what might make it fail.

What to look for: water evaporates, condenses on the glass and drips back (hydrosphere ↔ atmosphere); plants and microbes exchange CO₂ and O₂ (biosphere ↔ atmosphere); decomposers return nutrients to the soil (biosphere ↔ lithosphere). A jar may fail if it is too wet (mould), too hot, or too dark.

Grown-up note: wash hands after handling soil, and do not use soil or plants from roadsides or treated lawns.

Just for fun

What did the ocean say to the shore?

Nothing. It just waved. (Then it slowly eroded the shore, because the hydrosphere never stops interacting with the lithosphere.)

Your turn

Name the four spheres and give one thing found in each.

What are the two most common gases in the atmosphere, with their approximate percentages?

Why is soil a good example of overlapping spheres?

Name the two spheres involved in photosynthesis, and what moves between them.

Why must matter be recycled on Earth, while energy must keep flowing in?

Give one interaction between the hydrosphere and the lithosphere.

Your sealed jar has droplets on the inside of the glass every morning. Explain where they come from.

More practice: warm-up

Which sphere includes groundwater?

Which sphere includes mushrooms?

Is a volcano mostly part of the lithosphere or the atmosphere?

What is the main source of energy for nearly all ecosystems?

What does sustainability mean for an ecosystem?

More practice: on your own

A large area of forest is cut down and the land is paved for a parking lot. Name two spheres (other than the biosphere) that change, and how.

Explain how a decomposer, such as a fungus on a fallen log, links the biosphere and the lithosphere.

How can a volcanic eruption on the other side of the world affect weather in Canada?

Why do scientists say the ocean is important in the climate system?

A student says, "The lithosphere is not alive, so it doesn't matter for ecosystems." Correct this statement.

Challenge

Spring snowmelt in Ontario carries road salt into a stream. Trace this change through at least three spheres.

Design a fair test using two sealed jar ecosystems to find out whether light is needed to keep the jar ecosystem healthy. State your independent variable, dependent variable and two controlled variables.

Explain why scientists studying climate change need to understand all four spheres, not just the atmosphere.

Check your understanding

Quiz

Which sphere includes Earth's groundwater and glaciers?

About what percentage of the atmosphere is nitrogen?

Which process moves carbon dioxide from the atmosphere into the biosphere?

Why must energy keep entering ecosystems from the Sun?

Rain slowly dissolves a limestone cliff. Which two spheres interact?

Which statement best explains why sphere interactions matter for sustainability?

For parents and teachers

Big idea (B2.1): Earth works as one system of four spheres. Ecosystems are sustainable because matter keeps cycling between the spheres and energy keeps flowing through them from the Sun. The sealed-jar activity is a long-term observation investigation (A1.2), and the research questions build A1.1 skills.

How to help: On a walk, point at things and ask "Which sphere?" and then "What is it trading with the other spheres?" Help set up the jar and check it together each day; a photo log works well.

Common difficulties:

Thinking each object belongs to only one sphere. Soil, clouds and living things all involve several spheres. Overlap is the point.
Saying energy is recycled. Matter cycles; energy flows through and leaves as heat.
Forgetting groundwater and ice are part of the hydrosphere.

Sources: atmospheric composition and general Earth-system facts are standard (NASA, NOAA).