Some doomer authors have claimed that we're running out of resources in general. Not just fossil fuels, but many resources necessary for civilization, like metals, fertilizer, and so on, will soon be exhausted, according to them.
A notable example of this view, is the book Limits to Growth, which is perhaps the greatest doomer classic of all time. That book contains repeated claims that we will soon exhaust "minerals", "aluminum", and various other resources in the fairly near future. It shows graphs of depleting aluminum supplies and depleting supplies of various other things as time goes on, with near-zero rates of extraction for various resources by mid-century.
In this article I will argue that we have virtually inexhaustible supplies of everything necessary for modern civilization and for a large population. I will argue that we aren't running out of any essential resources or minerals, and that we don't face peaks of anything irreplacable. In fact, I'll show that we have enough resources to provide a large population with a first-world standard of living for billions of years, until our Sun explodes.
Note that I'm not claiming we'll never run out of anything. Clearly we will eventually exhaust our supplies of fossil fuels and other things. What I am claiming, however, is that we'll never run out of anything essential. By "essential" I mean resources for which there are no obvious substitutes, and which are required for modern civilization to exist with a large population. For example, iron, aluminum, fertilizer, and adequate energy sources are essential and have no substitutes. On the other hand, fossil fuels are absolutely not essential for civilization, since they're used as a portable energy source and they have many (albeit more expensive) alternatives. Fossil fuels are a cheap convenience, that is all.
Obviously there is some question of whether civilization has enough time to transition to other sources of energy and other minerals as fossil fuels and rare earths are exhausted. I will not address that question in this article. All I am attempting to answer here is whether there are enough resources to support modern civilization for 10 billion humans, and for how long, using any substitutes possible, even if that means we must revert to electrified public transportation like trolleys, and must manufacture hydrocarbons for the niche uses (like tractors) which can't be electrified. I will address questions of how quickly we can transition (and whether it's quickly enough) in a subsequent article.
In order to estimate whether we'll run out of anything essential, we must determine three facts: 1) which elements and substances are essential for modern civilization, in other words, which elements are needed and have no substitutes; 2) how much of them exist in the Earth's crust, in a form which could be economically extracted; and 3) how much of them we're using on a yearly basis, in other words, how quickly we're depleting them. Once we have those three pieces of information, we can project how long we have until we exhaust essential resources and civilization must end.
Of course it matters a great deal what future consumption patterns will be like and how large the population will be. A larger and richer population will exhaust resources more quickly. A population which is exponentially larger could obviously deplete resources very quickly. For this article, I am assuming that the human population will eventually stabilize at a high level (10 billion) as demographers predict, and those 10 billion people will reach European standards of living. Obviously, if the population continues to grow indefinitely, then we will eventually hit some limitation which constrains the further growth of population. Note that hitting a limit of population would happen as we ran out of one resource (probably arable land) which serves as a bottleneck. It would not necessarily cause an industrial collapse or a reversion to medieval mode of life or anything similar. It would probably cause starvation in the countries which were then poorest and had the highest population growth rates.
Which substances do we need for civilization?
Obviously we need various things for modern civilization. We need objects of civilization, like buildings, bridges, trains, and so on. We also need energy in large quantities, in order to build to objects of civilization and to extract the minerals necessary for their construction. We also need food (and therefore fertilizer) sufficient for 10 billion people.
However, just saying that "we need buildings" doesn't answer any questions. What are buildings made out of? We must decompose buildings into their constituent substances, and find out how much we have. Furthermore, we must also decompose the other objects of civilization (trains, computers, etc), into their constitutent substances. We must also find out what fertilizer is made from, and so on. In other words, we must decompose civilization, and find out which minerals and substances are absolutely required to build and sustain it.
Remarkably, almost everyting in civilization is made out of a very small number of elements, which are already mined in massive quantities. For the most part, civilization is built out of: iron, aluminum, silicon, oxygen, calcium (for cement), nitrogen, hydrogen, potassium, and phosphorous. Those elements are the "macro elements" of civilization, and I'll refer to them as such from now on, because they are required in huge amounts and they have no substitutes. Those macro elements are remarkably diverse and are sufficient by themselves to manufacture almost everything we need, including: cement, buildings, bridges, skyscrapers, roads, industrial machinery, power plants, trains, transportation infrastructure, generators, power cables1, computers, glass, steel, plasticky substances, trucks, fuels, ships, houses, and almost everyting else. Also, those macro elements include the major constituents of fertilizer (nitrogen, potassium, phosphorous). Also, those macro substances include the major constituents of reinforced concrete (silicon, oxygen, calcium, iron, and a little carbon), and concrete is the most common material in modern civilization by a very wide margin. Also note that these macro elements are already traded in large quantities and are used for precisely those purposes, so I'm not being theoretical here. Note also, that it's entirely possible to make plasticky things out of silicon and oxygen; carbon is not necessary for this purpose (although it's slightly cheaper). Remarkably, most of civilization is "built" out of large amounts of very few minerals.
In addition to those macro elements, we need a few other elements, in small amounts. I'll refer to these as the "micro elements." We need carbon in small amounts because it's needed for steel, and for drug making. We also need trace minerals, in extremely small amounts, for fertilizer (zinc, magnesium, sulphur, chlorine, sodium, and a very few others). We also need Uranium in small amounts if we choose to generate our energy using nuclear power, and we need its byproducts for nuclear medicine and smoke detectors.
Of course, at present we also use other trace minerals, like rare earths (for magnets), lithium (for batteries), nickel (batteries), platinum (catalytic converters), mercury (thermostats), copper (luxury cookware, luxury stereo cables1), chromium (chrome-plated objects), gold (jewelry, rapper dentistry, luxury stereo connectors) and so on. All those things are either unnecessary or have obvious substitutes. We can make batteries out of zinc, magnets out of other metals, and flat computer monitors using OLEDs (chemical formula: Al(C9H6NO)3. Remarkably, we can now even make flat screens out of the macro elements listed above; flat screens and batteries are the commonest uses by far of minerals other than the macro elements). We can forgo chrome-plated objects, jewelry, and luxury cookware.
Note also that we don't require fossil fuels, either for transportation or for any other essential purpose. For transportation we can easily substitute the kinds of transportation which prevailed before cars were common: trolleys, steetcars, trains, buses, and so on; and those are electric or can easily be electrified. Or we could use plug-in cars, as those become cheaper. In the few cases where there is no obvious way to electrify something (like ships) we can easily use alternative fuels like woody biomass in steam boilers (the small amount of carbon already listed in "micro elements") or anhydrous ammonia, which is a combustible fuel and which can be easily manufactured from nitrogen and hydrogen (listed among the macro elements), provided we have energy.
In addition to the elements listed above, we also need energy. In some ways, energy is the master resource, insofar as it allows us to extract the minerals and elements found above. We need energy for many essential purposes in civilization: to mine the minerals, to extract the minerals from their oxides, to transport the minerals, to build the objects of civilization, to fix nitrgoen for fertilizer manufacture, to manufacture the fuels for the few forms of transportation which cannot be electrified, and to supply the basic needs of civilization like lighting, heating, air conditioning, computing, communication, and so on.
It's difficult to determine the minimum amount of energy required for civilization, so let's make a liberal guess and say that we need 30 MwH of thermal energy per person per year, for 10 billion people. (This number is much higher than present per-capita energy expenditures worldwide). As a result, we would need about 300 petawatt-hours of thermal energy worldwide.
Finally, we also need fresh water to grow plants, and space to grow them. Presumably we would need cropland, although we could use hydroponic agriculture on a large scale if it were really necessary. Already, crops are grown in large quantities in hydropnic greenhouses in some parts of the world. Soil is not actually a requirement for agriculture if you have fertilizer. However, let's ignore this substitute and assume that we'll need cropland.
So there we have it. We've completed our catalog of what's necessary for civilization: 8 macro elements, a few micro elements, 300 petawatt hours of energy per year, fresh water, and cropland.
How much do we have?
Now that we've listed the elements and substances which are absolutely required for civilization, let's take stock of how much of them are available, and how much we need.
First let's start with the "macro elements" listed in the prior section, which we need in huge quantities. They are: iron, aluminum, silicon, oxygen, calcium, nitrogen, hydrogen, potassium, and phosphorous. Happily, five of those elements (out of nine) are super-abundant in the earth's crust. Iron, aluminum, silicon, oxygen, calcium, and potassium combined make up about 94%2 of the earth's crust by volume and can be found in fairly high concentrations virtually anywhere you put your foot down. For the most part, the Earth's surface is made out of those elements. Of the remainder, hydrogen can be acquired from seawater using electrolysis, and nitrogen is the primary component of air (60%). Phosphate is the only one of the "macro elements" which is not super-abundant, in truly massive quantities, almost everywhere. Phosphate is required for fertilizer, and I'll speak more about it later.
Let me repeat this fact. All of the macro elements except phosphorous are available in essentially inexhaustible amounts, since the Earth is made almost entirely out of them. Furthermore, those macro elements are sufficient to make almost all the objects of civilization. As a result, we could cover the entire terrestrial surface of the Earth in a miles-deep layer of concrete, glass, power cables, fertilizer, industrial machinery, skyscrapers, computers, and plasticky crap3, and we still wouldn't have run out of minerals or come anywhere close to it.
What about the "micro elements" like zinc and magnesium (for fertilizer) and carbon? Those are also available in truly massive quantities relative to the amounts which we require. For example, magesium constitutes 2% of the Earth's crust, which is 2000x more abundant than oil ever was despite being needed only in milligram quantities per person.
Now let's deal with energy. Let's assume we need 30 MwH/person/year thermal for advanced civilization (as we said before). With ten billion people, we'll need 300 Petawatt-Hours per year of thermal energy. (Of course, thermal energy can be converted to electricity by solar thermal power plants). Let's calculate how many solar thermal panels we'd need to capture that amount. The surface of the earth is bombarded by 89 petawatts continuously. Of that, 25% ends up on land, of which 14% ends up on desert. So deserts worldwide are continuously bombarded with (89*.25*.14=) ~3 petawatts, which is (3*24*365) ~26,000 PwH per year. Which means we would need to cover (300/26000) 1.1% of the Earth's deserts to capture the amount of energy we need to sustain advanced civilization for 10 billion people. In other words, we could obtain almost 100x more energy than we require using only solar panels in deserts. Of course, solar thermal is not the only source of energy available to us. There are also many other sources of energy, like offshore windfarms and breeder reactors. There is also the possibility of nuclear fusion, which isn't ready yet but which conceivably could come online within the next few hundred years, and which would multiply the amount of energy available to us by a huge factor.
Of course, solar panels require mineral resources for their construction. However, we have more than enough resources to build the solar thermal panels necessary to capture that amount of energy. Solar thermal panels are made mostly out of glass, which is silicon and oxygen, which constitute over 60% of the Earth's crust and which are found in massive quantities in the sand beneath the solar panels.
All that remains are freshwater and arable land. Freshwater can easily be obtained from seawater using desalinization plants (of course desalinating would require energy, but the amounts of energy required per person for desalinization are modest, and we obviously have enough of it; see above). As far as arable land is concerned, we have enough already to feed 10 billion people if we increased agricultural productivity per hectare to first-world standards throughout Asia, by the application of fertilizer, of which we have virtually inexhaustible amounts, because it's made from the macro elements listed above. Of course, we have many other options for growing crops, like irrigating the massive unused land areas, by desalinating water and digging canals.
In short. We are not running out of anything essential, other than phosphorous, which I'll deal with later.
The next million years
From the previous section, we can see that we have vastly more resources than we require. We're not running out of anything essential in the foreseeable future. But what about the longer run? If we have millions of years' worth of minerals, won't we run out eventually, if only in the far future?
No. All of the "macro elements" needed in large quantities (aluminum, iron, silicon, oxygen, calcium, nitrogen, hydrogen, potassium) are inifinitely recyclable, and are not being used up at any rate. When we mine these minerals and then throw them away, we have not affected the amount of them available in the Earth's crust at all. They will gradually return to the oxidized state in which they were found originally. Then we can re-mine them from landfills and separate them again, provided we have energy (which we do).
Nor are the "macro elements" being "dispersed" by our mining them, as some doomer authors have claimed4. The macro elements are already found in high concentrations all around the globe, and so won't be dispersed in any meaningful way by our mining them. Even if we mined all of those macro elements everywhere on the Earth's surface, and then scattered them at random all around the globe, they would still constitute 91% of the Earth's crust and so would be in high enough concentration everywhere to warrant economical separation and re-mining.
Nor would we gradually exhaust our supplies of fresh water. When we desalinate ocean water and use it for crops, that water will eventually evaporate into the atmosphere, condense, and rain again into the oceans, where we can desalinate it again provided we have energy. Similarly with fixed nitrogen for fertilizer: we can separate nitrogen out of the air over and over, provided we have energy.
Of course, all of this recycling depends upon energy. Clearly, energy is the master resource, upon which everything else depends.
However we have 100x more energy than we need, just from solar alone. This flow of energy will be continuous (more or less) for billions of years. Thus, we do not face any shortage of energy, which means that we don't face any shortage of anything else essential either.
The sole exception is phosphorous. Phosphorous is needed for fertilizer and is a basic component of life, thus it has no substitutes. Phosphorous is mined from phosphate rocks which will be exhausted within 1,000 years. Phosphorous cannot be re-extracted or recycled from the environment, because it actually is being dispersed as we use it: it doesn't exist in high enough concentration everywhere for us to throw it away at random (actually to allow it to run-off into the ocean) and recover it later, since it subsequently will be much more thinly dispersed. At some point we will start to run out of phosphorous, and will have to be more careful with its use. At some point we'll need to recover phosphorous from sewage and from dead bodies, instead of throwing it away or burying it.
Other than phosphorous, we face no shortages of any essential substances or elements for the foreseeable future. There is no reason, right now, to conclude that we will "run out" of any essential elements within the next million years.
Brief diversion: an unusual resource
One element which deserves special mention is silicon. Silicon is a remarkable element, insofar as silicon atoms can be "chained together" (like carbon) to form a limitless array of complicated molecules with very diverse chemical properties. Silicon is a "master mineral" insofar as you can make almost anything out of it. Using silicon and oxygen, you can make glass, or metals, or conductive wires, or electrical insulators, or plasticky substances, or fleshy sex toys, or fiberglass, or gels, or caulks, or clothing, or building materials, or breast implants, or silly putty, or opaque substances, or transparent substances, or liquids, or combustible fuel, or turbines. Silicon can also be used to make computer chips, wires, fiber optics, and electronics. It's not the ideal material for many of these purposes, but it is a possible substitute for all of them.
Remarkably, silicon and oxygen are the most prevalent elements in the Earth's crust, by far, together constituting 60% of the Earth's crust by volume. Silicon and oxygen are the main constituents of dirt, sand, and rocks.
This fact deserves special consideration. We can re-arrange the atoms in sand and make a computer, including the case.5 Or, we could also make a train. Or a building, including insulation, wiring, and windows.
Silicon and oxygen therefore constitute the "ultimate backdrop" among mineral resources. They are the ultimate substitute, because they can take on so many different properties by re-arranging their molecular structure, and because they are available in such massive quantities. Silicon and oxygen are so common that they're usually the "dirt" which we throw away when we're trying to mine other things.
In fact, it would likely be possible to build all the necessary objects of civilization, except fertilizer, from silicon, oxygen, aluminum, water, and thermal energy6. Remarkably, even computers and high-tech equipment are made overhwlemingly from this substance.
The versatility and massive supplies of silicon should be considered every time we hear a doomer claim that "we are RUNNING OUT of x and there are no possible substitutes." Whatever "x" is, it most likely could be made from sand, which is mostly silicon. In the few cases where it cannot, we have many, many alternatives.
We will never just "run out" of essential resources. Instead, we'll eventually need to undergo a transition, from exhaustible resources, to inexhaustible ones. For example, we'll eventually need to move away from fossil fuels, to other sources of energy which are vastly more plentiful. We'll also need to transition from internal-combustion cars, to electrified transport. We'll also need to replace our very small usage of limited minerals (like cobalt) with obvious alternatives. After we have done so, we'll have enough resources and energy to provide 10 billion people with a 1st-world standard of living for the next few billion years.7
Whether we have the wisdom to make this transition before civilization collapses, is another topic which I'll address in a subsequent article. The point I'm making here is that we don't face any inevitable decline of civilization solely from exhaustion of essential resources. There is no mathematical law or curve which implies that civilization must end. There is no law of nature or ecology or thermodynamics which implies that we're about to run out of resources or energy. We face a gradual transition; that is all. Whether we have the wisdom to make that transition is another topic.
Of course, we will always require huge amounts of the "master resource"--energy. Energy is what allows us to extract and re-extract all these resources. Happily, we have vastly more energy than we require, and we will have vastly more for billions of years.
The only pressing shortage is phosphorous, for fertilizer. At some point fairly soon (within 1000 years), we'll need to stop wasting phosphorous. We'll need to start recycling sewage to recover phosphorous, rather than allowing it to dissolve or flow into oceans. Happily, we won't need to start recycling phosphorous until after everyone on this planet has already reached a 1st-world standard of living, and when the expense of recycling it will be quite tolerable.
When I started learning about these things, years ago, I was shocked to discover just how few minerals are required to make almost everything we need to sustain civilization. That's the magic of chemistry, I suppose. Already, almost everyting is made overwhelmingly out of iron, aluminum, silicon, oxygen, calcium, hydrogen, nitrogen, potassium, and phosphorous (plus carbon, but the carbon is not essential for almost anything we build). I was also quite amazed to find that precisely those minerals, which we require in large amounts, constitute 91% of the mass of the Earth's crust and are essentially what this planet is composed of. What a fortunate coincidence: we are living on a massive planet made of precisely what we need.
 Copper is not required for wires or cables--not even for computer cables. Aluminum is suitable for this purpose, although slightly worse. Already, most ethernet cables are made out of aluminum, not copper.
 I am not saying it's desirable or possible to cover the surface of the Earth with a miles-deep layer of plasticky crap. I'm saying we have enough mineral resources to do it.
 This claim of "dispersing elements" has repeatedly been made by the ecological economics school of thought, especially by Herman Daly. While this argument is true for some minerals, it does not apply to the macro elements I listed, since those macro elements are found in high concentations everywhere no matter where we scatter things, so they'll never need to be "filtered" out.
 Of course, it's not possible to make computer chips solely from silicon. We must also use boron to dope the silicon wafers. Boron must be added in concentrations of at least 1 part per 100 million. We have enough boron for this, since computer chips are very small and boron is not rare, and we require only 1 part per 100,000,000. Also, we would need monitors, which can be made using OLED technology. OLEDs are made from aluminum, nitrogen, hydrogen, and oxygen, which are all among the macro elements listed, plus a little carbon, which is among the micro elements listed. Remarkably, even flat screens can now be made from the macro-elements I listed. This is important because flat screens and batteries are two of the commonest uses of rare minerals.
 Except computers, which, as I pointed out in note #3, require trace amounts of the element boron, which we also have in massive quantities relative to our requirements.
 A more in-depth examination of our resource future can be found in the paper The Age of Substitutability, H. E. Goeller and Alvin M. Weinberg, Science, 191 (1976), pp 683-689. They take a different approach to explaining these issues from the approach I've taken, insofar as they're more mathematical. Also, they do not touch upon the many uses of silicon or dwell upon computers, since those were rarely used in 1976. Also, they assume far less energy is necessary for civilization than I have assumed.