Energy sources are a big topic of conversation these days. With fossil fuels being both damaging to the environment and increasingly difficult to acquire, we’re looking into a wide variety of alternatives — some of which are cutting-edge, and others of which are very old indeed.

The one option that’s been with us from the start has been muscle power. Our own to begin with; later, after we domesticated animals, we got to use theirs instead. For millennia, everything from agriculture to textile manufacture to metalworking has been carried out with sweat and toil, fueled by the food we and our livestock eat. But of course, you can’t elbow grease your way to everything. No amount of direct labor will cause food to cook, nor pottery to harden, nor ores to smelt.

For that, we needed fire.

The question of when hominids first began using fire is one for archaeologists to ponder. Suffice it to say, very few authors are going to be writing about periods before that happened. Fire opened up countless doors for humanity, letting us stay warm in the winter, develop new and better materials, and even extract more calories from the food we eat.

How do you make fire, though? The earliest uses were probably opportunistic, with humans borrowing and perpetuating flames produced naturally, e.g. by lightning strike. Even after we learned to create fire ourselves, we had a strong tendency work with what we had keep it going rather than starting it from scratch: light one candle from another, carry a hot coal in a box to ignite another flame elsewhere, bank the fire at night so you can puff it up from the embers the next morning. We’ve even built rituals around this, especially with sacred fires, or marking the new year by starting our fires anew. In the absence of ritual, however, we prefer to work from an existing fire because creating one from nothing is difficult and time-consuming. You need oxygen — okay, the air provides that — and fuel — easy enough — but you also need heat.

Fire drills are an early tool for this end. They come in various forms, but they all operate by using friction to generate heat and eventually a coal, which can be used to light tinder. Similar tools are referred to as ploughs, saws, and thongs, depending on their form. Your next option is fire by percussion, striking two objects together to create a spark. Flint and steel are the most well-known variant, but other stones can work, like quartz or agate, and iron pyrite can strike sparks off itself. This tends to be easier than a fire drill, and it was hugely common up until the invention of chemical firestarters. In both houses and traveler’s packs, you were likely to find a tinderbox, containing some kind of striking materials and easily ignitable material, such as twigs, dried moss, certain types of fungi, paper, or charcloth. It was a basic and ubiquitous tool of life. Even now, lighters use percussion to create the spark that will burn the liquid fuel inside: a tiny and effective tinderbox equivalent.

Once you have fire, what do you use it on? Pretty much anything that can be persuaded to burn. We often think in terms of wood, and certainly that’s been used — but actually, wood is a fairly inefficient fuel, especially depending on the type. Charcoal is better, as it removes practically everything but the combustible carbon from the starting wood. Both Europe and Asia were using actual coal by the late European Middle Ages; you can also burn dried peat, the soggy precursor to coal. In fact, you can burn dried lots of things, including seaweed and dung — the latter being common in areas that lack much in the way of trees.

This isn’t just a matter of descriptive detail in the background of a scene. Fuel sources were causing localized environmental change long before the modern day. Much of the Near East used to be forested, before the advent of pottery and bronze-working consumed huge numbers of trees. Wars, too: Roman conquests were partly spurred by the need to secure new sources of wood after deforesting the ones under their control. The depletion of peatlands (which form far more slowly than they can be restored) has been called the original fossil fuel crisis. Not all of this is driven by our need to burn things for energy — we also use both wood and dried peat for construction — but it’s played a significant role.

And that role has only increased with the use of modern fossil fuels, like petroleum and natural gas. Not only are they major factors behind the current climate change crisis, but they’ve shaped our politics and our history in profound ways. Areas rich in these resources have experienced a boom in wealth . . . but usually only for the elite, while the poor suffer the destructive environmental effects of extraction. Meanwhile, foreign powers fight wars to make sure the faction in control will continue to sell them oil or gas at favorable prices.

All of these are reasons why we’re currently looking at more sustainable sources of energy. Solar power is mostly a new development; in the past it was largely restricted to sun-drying foods or mud bricks, or perhaps focusing its light enough through a crystal or glass lens to start a fire. But we’ve been building mills on the banks of streams and in windy areas for a long time, taking advantage of nature’s own energy to turn the millstone and grind our grain. With a bit more engineering, you can even build things like water-powered hammers, taking some of the grunt work off human shoulders.

The challenge there is less about the source of energy, and more about how we can best deploy it. Prior to the modern era, waterwheels and windmills were only helpful on the immediate premises. Not until we started figuring out electricity and batteries could we generate power in one place and use it in another. That’s the big hurdle now: figuring out efficient storage and transmission for wind, solar, or hydro power, so they can be relied upon in areas and at times where the sources aren’t available. (That, and mitigating the environmental damage of the mining necessary to produce the batteries and so forth.)

Nuclear energy was supposed to be our escape from all these limitations, but of course it comes with problems of its own. The scale of destruction it can wreak is huge, especially since the technology to make a reactor also lends itself to weapons of mass destruction. And we tend to find out the hard way what happens when you subject the surrounding infrastructure to that level of strain for years on end. You’re also left with some incredibly dangerous waste products, whose disposal we still don’t have a good solution for.

All our nuclear plants, though, operate on fission — on splitting the atom. The big question is whether we’ll ever develop nuclear fusion reactors. Those would be vastly safer; the problem is that you need incredibly high temperatures and pressures to make it happen, and we have yet to design a reactor that produces more power than you put in to make it go. Cold fusion was briefly the dream of the future, achieving the desired effect at normal temperatures, but it’s dubious whether that’s even physically possible.

In science fiction, often the energy question has been completely solved. Whatever future people are using to power their world, it’s ubiquitous, safe, and not destructive to the environment. A pipe dream this may be, but it’s a nice one to have: just as mastering fire opened many doors for early humans, achieving cheap and sustainable energy would transform our world in so many ways.

Right now, the best we can do is focus on reducing our energy usage and weaning ourselves off fossil fuels. We don’t want to go back to the days of having to do everything by hand.