The Earth and its atmosphere · System
A planet with limits: resources and recycling
Everything manufactured on Earth came out of the crust, and the crust is not being topped up. Recycling sends some of it round again — but only some, and how much depends on the material, not on how carefully you sort it.
Start here
About three quarters of all the aluminium ever smelted is still in use today.
Smelting began in the 1880s. Roughly 75% of every tonne produced since is still in a window frame, an engine block, a can or a plane — not in a hole in the ground. Almost no other material comes close.
What does that tell you?
Aluminium can be melted and cast again almost without loss, so the amount in circulation keeps building up. But the stock in use is still growing, which means new metal is still being dug up every year — recycling is not keeping pace with demand. A material can be almost perfectly recyclable and the world can still be mining more of it.
Ores, crude oil and phosphate rock took tens of millions of years to concentrate, and we are using them in centuries. On any human timescale the supply is finite: extraction is a one-way trip out of the crust.
Recycling is the only thing that sends any of it back. The question this lesson answers is how much comes back — and that turns out to be a property of the material.
The bench · run the loop
Start with 1000 kg. See how far it goes round.
1 of 5 materials opened
Pick a material
How much gets collected
Change the collection rate to finish this bench.
Aluminium can
Melts and casts again with almost nothing lost. The metal does not care how many times it has been round.
Lifetimes per kg of ore
1.00×
Used once, then gone.
Energy, new from ore
170 MJ/kg
What it costs to make the material the first time.
Energy, from recycled
8.5 MJ/kg
95% less than new.
Nothing comes back. Every kilogram used is a kilogram out of the ground, used once and finished — whatever the material is capable of.
Aluminium can
Melts and casts again with almost nothing lost. The metal does not care how many times it has been round.
Lifetimes per kg of ore
1.31×
Adding up every pass through the loop.
Energy, new from ore
170 MJ/kg
What it costs to make the material the first time.
Energy, from recycled
8.5 MJ/kg
95% less than new.
The multiplier is 1.31. The material would go round well; not enough of it is being collected to find out.
Aluminium can
Melts and casts again with almost nothing lost. The metal does not care how many times it has been round.
Lifetimes per kg of ore
1.90×
Adding up every pass through the loop.
Energy, new from ore
170 MJ/kg
What it costs to make the material the first time.
Energy, from recycled
8.5 MJ/kg
95% less than new.
A kilogram of ore does the work of about 1.9 kilograms — a real gain, and still a leaking loop. Look at how fast the bars shrink.
Aluminium can
Melts and casts again with almost nothing lost. The metal does not care how many times it has been round.
Lifetimes per kg of ore
6.90×
Adding up every pass through the loop.
Energy, new from ore
170 MJ/kg
What it costs to make the material the first time.
Energy, from recycled
8.5 MJ/kg
95% less than new.
A kilogram of ore now does the work of about 6.9 kilograms — this loop is running about as well as a loop ever does — and each pass costs 95% less energy than making it new.
Steel can
Magnetic, so it sorts itself out of mixed waste. Small amounts of other metals build up, which limits what the steel can be used for.
Lifetimes per kg of ore
1.00×
Used once, then gone.
Energy, new from ore
25 MJ/kg
What it costs to make the material the first time.
Energy, from recycled
7.5 MJ/kg
70% less than new.
Nothing comes back. Every kilogram used is a kilogram out of the ground, used once and finished — whatever the material is capable of.
Steel can
Magnetic, so it sorts itself out of mixed waste. Small amounts of other metals build up, which limits what the steel can be used for.
Lifetimes per kg of ore
1.30×
Adding up every pass through the loop.
Energy, new from ore
25 MJ/kg
What it costs to make the material the first time.
Energy, from recycled
7.5 MJ/kg
70% less than new.
The multiplier is 1.30. The material would go round well; not enough of it is being collected to find out.
Steel can
Magnetic, so it sorts itself out of mixed waste. Small amounts of other metals build up, which limits what the steel can be used for.
Lifetimes per kg of ore
1.85×
Adding up every pass through the loop.
Energy, new from ore
25 MJ/kg
What it costs to make the material the first time.
Energy, from recycled
7.5 MJ/kg
70% less than new.
A kilogram of ore does the work of about 1.9 kilograms — a real gain, and still a leaking loop. Look at how fast the bars shrink.
Steel can
Magnetic, so it sorts itself out of mixed waste. Small amounts of other metals build up, which limits what the steel can be used for.
Lifetimes per kg of ore
5.81×
Adding up every pass through the loop.
Energy, new from ore
25 MJ/kg
What it costs to make the material the first time.
Energy, from recycled
7.5 MJ/kg
70% less than new.
A kilogram of ore now does the work of about 5.8 kilograms — this loop is running about as well as a loop ever does — and each pass costs 70% less energy than making it new.
Glass bottle
Endlessly remeltable, but the melting is most of the energy — so recycling glass saves far less energy than people expect.
Lifetimes per kg of ore
1.00×
Used once, then gone.
Energy, new from ore
15 MJ/kg
What it costs to make the material the first time.
Energy, from recycled
11 MJ/kg
27% less than new.
Nothing comes back. Every kilogram used is a kilogram out of the ground, used once and finished — whatever the material is capable of.
Glass bottle
Endlessly remeltable, but the melting is most of the energy — so recycling glass saves far less energy than people expect.
Lifetimes per kg of ore
1.29×
Adding up every pass through the loop.
Energy, new from ore
15 MJ/kg
What it costs to make the material the first time.
Energy, from recycled
11 MJ/kg
27% less than new.
The multiplier is 1.29. The material would go round well; not enough of it is being collected to find out.
Glass bottle
Endlessly remeltable, but the melting is most of the energy — so recycling glass saves far less energy than people expect.
Lifetimes per kg of ore
1.82×
Adding up every pass through the loop.
Energy, new from ore
15 MJ/kg
What it costs to make the material the first time.
Energy, from recycled
11 MJ/kg
27% less than new.
A kilogram of ore does the work of about 1.8 kilograms — a real gain, and still a leaking loop. Look at how fast the bars shrink.
Glass bottle
Endlessly remeltable, but the melting is most of the energy — so recycling glass saves far less energy than people expect.
Lifetimes per kg of ore
5.26×
Adding up every pass through the loop.
Energy, new from ore
15 MJ/kg
What it costs to make the material the first time.
Energy, from recycled
11 MJ/kg
27% less than new.
A kilogram of ore now does the work of about 5.3 kilograms — this loop is running about as well as a loop ever does — and each pass costs 27% less energy than making it new.
PET bottle
The polymer chains shorten every time it is melted. Half of what comes back is only fit for something less demanding than a bottle.
Lifetimes per kg of ore
1.00×
Used once, then gone.
Energy, new from ore
85 MJ/kg
What it costs to make the material the first time.
Energy, from recycled
17 MJ/kg
80% less than new.
Nothing comes back. Every kilogram used is a kilogram out of the ground, used once and finished — whatever the material is capable of.
PET bottle
The polymer chains shorten every time it is melted. Half of what comes back is only fit for something less demanding than a bottle.
Lifetimes per kg of ore
1.14×
Adding up every pass through the loop.
Energy, new from ore
85 MJ/kg
What it costs to make the material the first time.
Energy, from recycled
17 MJ/kg
80% less than new.
Even collecting one in four, the multiplier is only 1.14. What comes back is degraded, so most of it cannot do the original job again.
PET bottle
The polymer chains shorten every time it is melted. Half of what comes back is only fit for something less demanding than a bottle.
Lifetimes per kg of ore
1.33×
Adding up every pass through the loop.
Energy, new from ore
85 MJ/kg
What it costs to make the material the first time.
Energy, from recycled
17 MJ/kg
80% less than new.
Even collecting half, the multiplier is only 1.33. What comes back is degraded, so most of it cannot do the original job again.
PET bottle
The polymer chains shorten every time it is melted. Half of what comes back is only fit for something less demanding than a bottle.
Lifetimes per kg of ore
1.82×
Adding up every pass through the loop.
Energy, new from ore
85 MJ/kg
What it costs to make the material the first time.
Energy, from recycled
17 MJ/kg
80% less than new.
A kilogram of ore does the work of about 1.8 kilograms — a real gain, and still a leaking loop. Look at how fast the bars shrink.
Crisp packet (metallised film)
Plastic laminated to a few microns of aluminium. No process separates the two layers economically, so almost none of it comes back as either material.
Lifetimes per kg of ore
1.00×
Used once, then gone.
Energy, new from ore
90 MJ/kg
What it costs to make the material the first time.
Energy, from recycled
90 MJ/kg
No recycling route, so no saving.
Nothing comes back. Every kilogram used is a kilogram out of the ground, used once and finished — whatever the material is capable of.
Crisp packet (metallised film)
Plastic laminated to a few microns of aluminium. No process separates the two layers economically, so almost none of it comes back as either material.
Lifetimes per kg of ore
1.01×
Adding up every pass through the loop.
Energy, new from ore
90 MJ/kg
What it costs to make the material the first time.
Energy, from recycled
90 MJ/kg
No recycling route, so no saving.
Collection is not the problem here — the material is. Even collecting one in four, a kilogram of ore does the work of only 1.01 kilograms, and the second bar has already all but vanished.
Crisp packet (metallised film)
Plastic laminated to a few microns of aluminium. No process separates the two layers economically, so almost none of it comes back as either material.
Lifetimes per kg of ore
1.01×
Adding up every pass through the loop.
Energy, new from ore
90 MJ/kg
What it costs to make the material the first time.
Energy, from recycled
90 MJ/kg
No recycling route, so no saving.
Collection is not the problem here — the material is. Even collecting half, a kilogram of ore does the work of only 1.01 kilograms, and the second bar has already all but vanished.
Crisp packet (metallised film)
Plastic laminated to a few microns of aluminium. No process separates the two layers economically, so almost none of it comes back as either material.
Lifetimes per kg of ore
1.02×
Adding up every pass through the loop.
Energy, new from ore
90 MJ/kg
What it costs to make the material the first time.
Energy, from recycled
90 MJ/kg
No recycling route, so no saving.
Collection is not the problem here — the material is. Even collecting nine in ten, a kilogram of ore does the work of only 1.02 kilograms, and the second bar has already all but vanished.
Reference · five things we take out of the ground
Tap one. Each has a different kind of limit.
1 of 5 opened
Not one of these runs out in the same way.
Bauxite — aluminium ore
The only ore aluminium is extracted from in quantity. Smelting it needs electricity on a scale that decides where smelters get built.
The limit: Plenty in the ground for now, but extraction is one of the most energy-hungry industrial processes there is, so the real limit is energy rather than rock.
Does recycling help? Enormously. Recycled aluminium takes about a twentieth of the energy, and the metal comes back as good as new.
Iron ore
Steel — buildings, cars, ships, tools, tins. By mass, the most used metal on the planet by a wide margin.
The limit: The most abundant of the useful ores, but the high-grade deposits get taken first, and lower grades need more digging and more energy per tonne of iron.
Does recycling help? Well. Steel is easy to separate magnetically, and a large share of new steel is already made from scrap.
Crude oil
Fuels, and the feedstock for almost every plastic, dye, solvent and synthetic fibre.
The limit: Formed over tens of millions of years from buried marine organisms, and used in a couple of centuries. Burning it also puts its carbon into the atmosphere.
Does recycling help? Not once it is burnt — that carbon is gone from the loop entirely. Plastics made from it can be recycled, but only a few times before the polymer is too degraded.
Phosphate rock
Fertiliser. Phosphorus is one of the few elements crops cannot be grown without and for which there is no substitute at all.
The limit: Concentrated deposits are in a handful of countries, and there is no alternative source. This is the resource limit with the sharpest consequences.
Does recycling help? In principle, from sewage and manure, and this is starting to happen. Phosphorus spread thinly on fields or washed into rivers is effectively lost.
Helium
Cooling the magnets in MRI scanners, and in welding and leak detection. Nothing else stays liquid at 4 kelvin.
The limit: Made underground by radioactive decay over hundreds of millions of years, and collected as a by-product of natural gas. Released to the air, it leaves the atmosphere for space and is gone for good.
Does recycling help? Only by capturing it before it escapes, which good MRI installations now do. Party balloons are a one-way trip.
Key fact
The Earth holds a fixed stock of every ore, and extraction is one-way. Recycling returns part of the material each time round, so one kilogram from the ground can serve several lifetimes — but every loop leaks, so recycling slows the loss and never stops it.
Five words
Say your answer out loud before you turn each card over. If you cannot say it, you do not know it yet.
Think again
“If we recycled everything, we would never run out of anything.”
You have just run the loop five times. Commit before you read on.
Every pass through the loop loses material. Some is never collected, some is lost in sorting and melting, and some comes back too degraded to do the original job. Even at nine collected out of ten, aluminium gets about seven lifetimes out of a kilogram of ore, not infinite lifetimes — and a crisp packet gets barely one, however carefully you put it in the right bin.
So recycling buys time; it does not make a finite stock infinite. The two things that actually cut extraction are using less and using it for longer — which is why reduce and reuse come before recycle, and in that order.
Mastery ladder
Not started yet.
Rungs 3 and 4 you mark yourself.
Rung 1 · Recall
Why is a metal ore described as a finite resource?
Rung 2 · The one that catches people
Nine out of ten crisp packets are collected, and nine out of ten aluminium cans are collected. Why does recycling do so much more for the cans?
Rung 3 · Explain
A council doubles its collection rate for plastic bottles and is disappointed that the amount of new plastic being made barely falls. Explain why, using what the bench showed you.
Rung 4 · Take it somewhere new
A smartphone contains around thirty different elements, each in tiny amounts and bonded into layers a few atoms thick. Predict how well it recycles compared with an aluminium can, and say what the designers would have to change.
Key note
Metal ores, crude oil and phosphate rock are finite: they formed over millions of years and are being extracted in centuries. Recycling returns part of the material to be used again, saving raw material and usually a large amount of energy — recycled aluminium takes about a twentieth of the energy of new metal from ore. But every loop loses some material, and some materials come back degraded or cannot be separated at all, so recycling slows extraction rather than ending it. Using less and using things for longer cut extraction more than recycling does.
Going further
You will see headlines saying a metal has a certain number of years left. Those figures move, and not because anyone found more planet. A reserve is the part of a resource that can be extracted at a profit with today's technology, so when the price rises or the mining gets cleverer, ore that was worthless becomes a reserve and the number of years left goes up. That does not mean the stock is unlimited — it means the cheap, concentrated part gets used first, and everything after it takes more energy to extract. The limit shows up as rising energy cost long before anything physically runs out.
The awkward one is the crisp packet. Plastic film laminated to a layer of aluminium a few microns thick is a brilliant piece of engineering — it keeps food fresh for months using very little material — and it is close to unrecyclable, because no process separates the two layers economically. That is a real trade-off rather than a mistake, and it is the shape of most recycling problems: the property that makes a material useful is often the same property that makes it hard to get back.
Before this lesson
Connects to
At GCSE this becomes
- Life-cycle assessment, and the extraction of copper from low-grade ores by phytomining and bioleaching.
Where to next
Ask Mr Badmus AI
Still not sure why recycling a can beats recycling a crisp packet?
Lesson content © MrBadmusAI.