What If? Lab

What if there were no soil?

Soil is the dark, crumbly ground where plants grow. It is full of tiny living things! What if there were no soil at all? Let's imagine it with Olly.

Soil is broken-down rock mixed with rotted plants and animals, plus water, air and huge numbers of living things. It holds plant roots, feeds them and soaks up rain, and UNEP says about 95 percent of our food comes from it. Under good conditions, one inch of topsoil can take hundreds of years to form. Imagine a world with no soil, and follow what might change.

Soil forms as parent material weathers under the influence of climate, organisms and relief over time (UC Cooperative Extension); one inch of topsoil can take 200 to 1,000 years even under favorable conditions. UNEP notes that 95 percent of food comes from soil. This thought experiment reasons about what might change without it, and how people care for the soil we have.

Explore

The big question

Soil is the ground where plants grow. It looks like plain dirt.

But soil is full of life! What if there were no soil anywhere?

Soil might look like plain dirt, but it is a mix of many things. Clemson University's soil guide lists soil particles, organic matter, water, air and living organisms. The particles are bits of broken rock: sand, silt and clay. The organic matter is what is left of plants and animals after they rot.

What if all the soil disappeared, leaving bare rock? In this thought experiment you can follow three paths: what happens to plant roots, what happens to the worms and fungi that live underground, and how soil forms in the first place.

Soil is a variable mixture of weathered minerals and decayed humus (University of Alaska Fairbanks Geophysical Institute), with water, air and living organisms (Clemson Cooperative Extension). Its three main kinds of particle are sand, silt and clay, whose proportions set its texture, which affects how much water and air it holds.

This thought experiment removes soil from the land and asks what might change for plants, soil organisms and the water that falls on the ground. It cannot say how soil might vanish; it reasons only from what soil does today and how slowly it forms.

Explore the idea

Make a prediction

How long can it take to make one inch of new topsoil?

Under good conditions, about how long can it take nature to make one inch of topsoil?

UC Cooperative Extension's estimate for forming one inch of topsoil under favorable conditions is…

200 to 1,000 years
About one week
About one year

Established fact
Soil holds plants, feeds them and is full of life.

Soil anchors and feeds plants, stores water and is home to huge numbers of living things; about 95 percent of our food comes from it (UNEP).

Soil supports nearly all food-producing plants, regulates water and hosts immense biodiversity (UNEP; Columbia University's Earth Institute).
Established fact
New soil takes hundreds of years to make.

Under good conditions, one inch of topsoil takes 200 to 1,000 years to form (UC Cooperative Extension).

Soil formation depends on parent material, climate, organisms, relief and time; UC gives 200 to 1,000 years per inch of topsoil under favorable conditions.
An idea scientists discuss
A world with no soil is pretend. We imagine what might happen.

What might happen with no soil at all is an idea built from what soil does today.

Every consequence of a soil-free world here is reasoned from present processes and might differ greatly in reality.
Established fact
Soil is made of tiny bits of rock, rotted plants, water, air and living things.

Soil is made of soil particles (sand, silt and clay), organic matter, water, air and living organisms.

Soil comprises mineral particles (sand, silt, clay), organic matter, water, air and living organisms; particle proportions set its texture (Clemson Cooperative Extension).
Established fact
Most of the food we eat grows in soil.

About 95 percent of our food comes from soil, the material in which nearly all food plants grow.

Soil is the foundation of the food system: 95 percent of food comes from soil, the medium in which nearly all food-producing plants grow (UNEP).
Established fact
In space, astronauts grow lettuce in little pillows.

NASA's Veggie garden grows each plant in a pillow filled with a clay-based growth material and fertilizer, which spreads water, nutrients and air around the roots.

Veggie's pillows of clay-based media and fertilizer keep water, nutrients and air balanced around roots, which might otherwise drown in water or be engulfed by air in microgravity (NASA).
An idea scientists discuss
Without soil, plants might have nowhere to put their roots.

Without soil, most land plants might have nowhere to anchor their roots, and growing enough food might be very hard.

Without soil, food production might depend entirely on engineered growth media; whether that might feed many people cannot be judged here.
Established fact
A handful of soil can hold millions of tiny living things.

A handful of soil can contain millions of bacteria and fungi, as well as tiny insects and microscopic animals called tardigrades.

A handful of soil can contain millions of bacteria and fungi, tiny insects and tardigrades; an estimated 360,000 animal species live in soil (UNEP, citing a European Commission report).
Established fact
Worms dig tunnels that let air and water into the soil.

Earthworms, insects, millipedes and other small animals feed on dead plants and burrow, letting in air and making paths for water and roots.

Soil invertebrates (insects, roundworms, millipedes, centipedes, earthworms) decompose plant material and burrow, aerating soil; microbes release CO₂ that helps dissolve minerals (UAF Geophysical Institute).
Established fact
One acre of soil can hold a lot of worms!

One acre of soil may contain 900 pounds of earthworms, 2,400 pounds of fungi and 1,500 pounds of bacteria.

Per acre, estimates of 900 lb of earthworms, 2,400 lb of fungi, 1,500 lb of bacteria and 133 lb of protozoa; a gram may hold a billion bacteria, 5 percent discovered (Columbia University's Earth Institute).
An idea scientists discuss
Without soil, worms and fungi might have nowhere to live.

Without soil, worms, fungi and bacteria might lose their home, and dead leaves might pile up and rot much more slowly.

Losing soil organisms might slow decomposition and nutrient return to plants; how fast leaf litter might accumulate cannot be estimated here.
Established fact
It can take hundreds of years to make one inch of topsoil.

Under good plant cover and the most favorable climate, one inch (about 2.5 centimeters) of topsoil takes 200 to 1,000 years to form.

Under good vegetative cover and favorable climate, an inch of topsoil takes 200 to 1,000 years; strongly developed soils indicate a million or more years of soil building (UC Cooperative Extension).
Established fact
Where glaciers left piles of rock and gravel, the first signs of soil came in about 15 years.

On ground left by Alaskan glaciers, the first traces of soil can appear in about 15 years, a surface layer in about 250 years, and a full soil in about 2,000 years.

On Alaskan glacial moraines, traces of soil formation appear within about 15 years, a surface loam in about 250 and a full profile in about 2,000 (UAF Geophysical Institute).
Established fact
People help soil with compost and by keeping plants growing on it.

UNEP suggests adding compost and mulch, keeping the ground covered with plants, and digging and plowing less to keep soil healthy.

UNEP's measures include raising organic matter (groundcover, mulch, compost), minimal tillage, retaining crop residues and year-round groundcover; it reports one third of the world's soil is degraded.
An idea scientists discuss
If soil were all gone, making it again might take a very long time.

If all soil disappeared, nature might need hundreds or thousands of years to make new soil deep enough for farms.

Rebuilding soil from bare rock might take centuries to millennia, depending on parent material, climate and colonizing organisms; no single figure applies.

In our world

Plants push their roots down into soil. The soil holds them up.

Soil gives roots water and food. Most of the food we eat grows in soil!

Soil holds plant roots in place and gives them nutrients, the chemicals plants need to grow. It also soaks up, releases and cleans water. UNEP says that about 95 percent of our food comes from soil, and that nearly all food crops grow in it.

Soil is also crowded with life. A handful can hold millions of bacteria and fungi, along with tiny insects and microscopic animals called tardigrades. An article from Columbia University's Earth Institute estimates that one acre of soil may contain 900 pounds of earthworms and 2,400 pounds of fungi.

Soil anchors roots, supplies nutrients and absorbs, releases and purifies water (Columbia University's Earth Institute). UNEP calls it the foundation of the food system: 95 percent of our food comes from soil, the medium in which nearly all food-producing plants grow.

Its biodiversity is immense. The Earth Institute article estimates that an acre may hold 900 pounds of earthworms, 2,400 of fungi, 1,500 of bacteria, 133 of protozoa and 890 of arthropods and algae, and that a gram may hold a billion bacteria, only 5 percent of them discovered. UNEP cites an estimate of 360,000 animal species living in soil.

Imagine no soil

Let's pretend all the soil is gone. Only bare rock is left.

Plants might have nowhere to put their roots. Rain might run off the rock. Let's find out why.

Now imagine the land with no soil, just bare rock. Most plants might have nowhere to anchor their roots and nothing to take nutrients from. Farms might not be able to grow crops in fields at all.

Rain might pour off the bare rock instead of soaking in, and the worms, fungi and bacteria that live underground might lose their home. Dead leaves might pile up with fewer living things to break them down. These are ideas: we reason from what soil does today.

Without soil, rooted land plants might lose both anchorage and their nutrient and water supply, and since UNEP traces 95 percent of food to soil, food production might depend on small, managed growth systems instead.

Water might run off rock surfaces rather than infiltrating, removing the absorption and slow release the Earth Institute credits to soil. Decomposition and nutrient cycling might slow sharply with the loss of soil bacteria, fungi and invertebrates. Rebuilding soil might take centuries for each inch, as the next sections show. These are reasoned ideas, not predictions.

How soil forms

Soil starts as rock. Over a very long time, rock breaks into tiny bits.

Plants grow, die and rot. Worms and tiny living things mix it all together. Slowly, it becomes soil.

Soil forms from parent material: rock that has broken down, or loose material carried by water, wind or ice. UC Cooperative Extension lists five things that shape soil: the parent material, the climate, plants and animals, the shape of the land, and time.

Living things do much of the work. Plant roots loosen the ground and add organic matter. Bacteria and fungi break down dead plants. Earthworms, insects, millipedes and other small animals feed on plant bits and burrow, letting in air and making paths for water and roots. Under good conditions, one inch of topsoil can take 200 to 1,000 years to form.

UC Cooperative Extension names five soil-forming factors: parent material, climate, vegetation and animal life, relief, and time. Climate and vegetation are the active forces; relief modifies them through runoff and temperature.

Microorganisms decompose plant matter, producing carbon dioxide that combines with soil moisture to dissolve minerals, and some bacteria fix nitrogen from the air (UAF Geophysical Institute). Soil invertebrates feed on plant material and burrow, aerating the soil. Rates depend on all five factors: UC gives 200 to 1,000 years per inch of topsoil under favorable conditions, while on young Alaskan glacial moraines a surface loam layer can develop in about 250 years.

Caring for soil

People can help soil stay healthy.

They add compost, keep plants growing over the ground, and dig less. Astronauts even grow lettuce in space, in little pillows!

Because soil forms so slowly, people work to protect the soil we have. UNEP suggests adding organic matter with compost and mulch, keeping the ground covered with plants all year, digging and plowing less, and using fertilizers and pesticides carefully.

Plants can grow in other materials too, with a lot of care. NASA's Veggie garden on the International Space Station grows each plant in a small pillow filled with a clay-based growth material and fertilizer. The pillows spread water, nutrients and air around the roots. Astronauts have grown lettuce, kale and zinnia flowers this way.

UNEP reports that one third of the world's soil is degraded, and lists ways to nurture it: raising organic matter through groundcover, mulch and compost; minimal tillage and retaining crop residues; planned rotational grazing; careful, targeted use of fertilizers and pesticides; and aiming for groundcover all year.

In space, plants are grown without garden soil using careful engineering. NASA's Veggie system uses pillows of clay-based growth media and fertilizer to balance water, nutrients and air around roots in microgravity, and has produced three types of lettuce, Chinese cabbage, mizuna mustard, red Russian kale and zinnias.

Amazing facts

Some soils are very, very old!

Some soils in California show a million or more years of soil building, while soil at a farming area in Alaska is mostly younger than 10,000 years.

UC Cooperative Extension notes that some Ventura County soils, with strongly developed subsoils or hardpans, indicate a million or more years of soil building; UAF's Geophysical Institute notes that soil at the Big Delta agricultural project in Alaska is post-glacial and typically younger than 10,000 years.
Astronauts have grown flowers in space!

NASA's Veggie garden has grown three types of lettuce, Chinese cabbage, mizuna mustard, red Russian kale and zinnia flowers.

Veggie, about the size of a carry-on bag and typically holding six plants, has grown lettuces, Chinese cabbage, mizuna mustard, red Russian kale and zinnias (NASA).
Just one gram of soil, a tiny bit, can hold a billion bacteria!

One gram of soil may hold one billion bacteria, and only about 5 percent of them have been discovered.

A gram of soil may hold a billion bacteria, of which only 5 percent have been discovered (Columbia University's Earth Institute).
Sunshine helps make soil.

Sunshine powers the weathering that breaks rock down and turns it into soil.

UAF's Geophysical Institute notes that sunshine powers both the physical and biochemical weathering needed for soil formation.

Words to know

soil: the top layer of the ground, made of bits of rock, rotted living things, water, air and life
parent material: the broken rock or loose material that a soil forms from
weathering: the slow breaking down of rock into smaller pieces
humus: dark material made from rotted plants and animals
topsoil: the upper layer of soil, with the most organic matter and tiny living things
decomposer: a living thing, such as a fungus or a bacterium, that breaks down dead plants and animals
compost: rotted plant scraps that people add to soil to help it

Discovery challenge

How much of our food comes from soil?

According to UNEP, about how much of our food comes from soil?

UNEP's figure for the share of our food that comes from soil is…
- About 95 percent
- About 5 percent
- None of it
Show the answer

About 95 percent

Almost all of it: about 95 percent!

About 95 percent, because nearly all food crops grow in soil.

…95 percent; soil is the medium for nearly all food-producing plants (UNEP).
Which animal digs tunnels that let air and water into soil?

Which animal burrows through soil, letting in air and making paths for water and roots?

Which of these soil invertebrates aerates soil by burrowing?
- Earthworms
- Goldfish
- Pigeons
Show the answer

Earthworms

Earthworms! Their tunnels let air and water in.

Earthworms, along with insects, millipedes and other small animals.

Earthworms, with insects, roundworms, millipedes and centipedes (UAF Geophysical Institute).
How long can one inch of new topsoil take to make?

Under good conditions, how long can one inch of topsoil take to form?

UC Cooperative Extension gives the time to form one inch of topsoil under favorable conditions as…
- 200 to 1,000 years
- About a week
- About a year
Show the answer

200 to 1,000 years

Hundreds of years: 200 to 1,000!

200 to 1,000 years, under good plant cover and climate.

…200 to 1,000 years, depending on the other soil-forming factors.
In the space garden, what do the plants grow in?

In NASA's Veggie garden on the space station, what does each plant grow in?

NASA's Veggie system supplies roots with water, nutrients and air using…
- A pillow of clay-based material and fertilizer
- A bag of sugar
- A bare metal tray
Show the answer

A pillow of clay-based material and fertilizer

A little pillow full of clay-based material.

A pillow filled with clay-based growth material and fertilizer.

…pillows of clay-based growth media and fertilizer (NASA).
In a soil jar test, which part sinks to the bottom first?

In a soil jar test, which part settles to the bottom within about a minute?

In Clemson's jar test, the layer that settles within one minute is…
- Sand
- Clay
- Silt
Show the answer

Sand

Sand! It sinks to the bottom in about a minute.

Sand settles first; the silt layer is marked after 2 hours and the clay after 48 hours.

…the coarse sand layer; silt is marked after 2 hours and clay after 48 (Clemson Cooperative Extension).

Experiments to try

Explore next

For parents & teachers

What children will learn

Soil is a mix of rock particles, organic matter, water, air and living organisms.
Soil anchors and feeds plants, stores water and supports almost all of our food.
Soil forms slowly from rock through weathering and the work of living things.
Thought experiments separate known facts from reasoned ideas.

Recommended ages: 7 to 17 · About 15 minutes

Talk about it

What do you think lives in the soil under your feet right now?
Why might farmers and gardeners add compost and keep plants growing over the ground?
If soil takes hundreds of years to form, how should we treat the soil we have?

Try at home or in class

Soil jar test (Clemson Cooperative Extension): a grown-up digs a cup of garden soil and sifts out stones and roots. Fill a clear jar with a lid (plastic is safest) one-third full of soil, top it up with water, close it tightly and shake. Mark the sand layer after 1 minute, the silt after 2 hours and the clay after 48 hours. Wash hands afterward.
With a grown-up and garden gloves, gently lift a log, stone or pile of leaves in a garden and look for worms, beetles and fungi. Put everything back as you found it, and wash your hands afterward.

Key vocabulary: soil, parent material, weathering, humus, topsoil, decomposer, compost

Where these facts come from

Formation and Classification of the Soil , UC Cooperative Extension Ventura County (University of California Agriculture and Natural Resources)
Soil Formation (Alaska Science Forum) , University of Alaska Fairbanks Geophysical Institute
Why Soil Matters , Columbia Climate School, State of the Planet (Columbia University)
What's the big deal about dirt? , UN Environment Programme
Growing Plants in Space , NASA
Soil Horizons , Soil Science Society of America, Soils 4 Teachers
Soil Texture Analysis "The Jar Test" , Clemson Cooperative Extension, Home & Garden Information Center

Checked, not yet human-reviewed. Last updated October 24, 2026. Spotted a mistake? Tell us.