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The theory of Late Heavy Bombardment says that approximately 4 billions of years ago, something disturbed the orbits of asteroids in the Kuiper belt, which caused extremely heavy bombardment of Earth by asteroids. This probably brought many heavy elements to Earth's surface. The heavy elements that were here previously, during the Earth's formation, sank to the core when the Earth was liquid which made them out of reach. In other words, if there was no Late Heavy Bombardment, the surface of Earth might have been almost without elements much heavier than silicon. (Iron, gold, silver, platinum and others would be extremely rare.)

My question: If humans developed the same way they did, what kind of technology would be achievable almost without elements much heavier than silicon?

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    $\begingroup$ What really matters for element abundances in the crust is not their weight, but their chemical properties, as described by the Goldschmidt classification. Elements classified as "lithophilic" tend to dissolve well in the lighter fractions of rock that float up to the crust. In fact, most of the "heavy metals", including the lanthanides and the actinides, are actually lithophilic, and thus enriched in the crust; notable exceptions are the "rare metals" iridium, platinum and gold, which are siderophilic, and so tend to sink to the core. $\endgroup$ – Ilmari Karonen Mar 6 '15 at 0:18
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    $\begingroup$ Also note that in most cases, what's present in the Earth's crust isn't pure elements, but compounds (that is, ores), which are much lighter. For instance, iron has a specific gravity around 7.0-7.5, various ores can be half that. Same with copper and a number of other metals: reade.com/Particle_Briefings/spec_gra.html $\endgroup$ – jamesqf Mar 6 '15 at 5:07
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I'm going to look at some major technologies, and see if they can be done without metals heavier than silicon (I'm going to assume sodium, chlorine, and other biologically needed minerals are still around, just because we need that to live. See sodium-potassium pumps. I'm also going to assume those do not occur in harvestable deposits, so we can only get them for biological purposes.)

  • Fire: $\checkmark$ Life really needs the stuff in the top right of the periodic table, so I think we would have plenty of stuff to burn.
  • Fired Clay: $\checkmark$ This was used for pots, which helped us store food and water. It also helps us make super good pizzas.
  • Knives: $\checkmark$ Obsidian was often used for knives. Ceramic knives could work, too, but not ones as we see today. Aluminum could work, but obsidian is better than aluminum for this.
  • Wheels: $\checkmark$ Wooden wheels!
  • Abacus: $\checkmark$ They're mostly made of wood
  • Sundial: $\checkmark$
  • Glass:$\checkmark$ As long as there is silica, $SiO_2$, we're set for glass
  • Camera Obscura: $\checkmark$ This represents one important advancement in optics. Combine this with a glass, and you get a basis for optics. This opens the way for telescopes and microscopes.
  • Printing Press: $\checkmark$ You can make this out of wood. The type would need frequent replacement.
  • Nautical Navigation: $\checkmark$ Polynesian Navigation could be used for sure. Astrolabes are usually made from metal, as wood warps. If you can protect your wooden astrolabe from warping, you could have it. Of course, you can make bits out of aluminum, as they do not experience crazy amounts of stress.
  • Drills and Other Tools: $\checkmark$ using obsidian, teeth, leather, and wood, you can make drills and other items. Your bits would wear down quickly, but it could happen. You could also use aluminum, and try to temper it with alloys to make edges harder.
  • Gunpowder: $\checkmark$ Here is the list of the basic ingredients for black powder. If we allow potassium, we're there. You could also use lithium nitrate.
  • Steam Engine: Maybe, as we need a good chamber to keep the steam in which allows it to be heated. Metals fill this role very well, but wood and other organic materials do not. You could use aluminum, though.
  • Electricity Generation: Likely No We really rely on magnets to generate electricity. You can make a solar cell with Si and C, but I do not know how you would transmit the current without Graphene (or Aluminum), which would be your best option. Aluminum would be great at transferring current, but it is not magnetic, so you couldn't use it as a magnet.
  • Computer: Maybe. Mechanical Computers exist, but they do tend to rely on tight-fitting metal pieces. Wood may work, but would require a very controlled environment, so aluminum would be a better bet.
  • Semiconductors: Maybe Since most semiconductors are mostly silicon, and some are made of organic materials, you could have semiconductors.

I'm going to stop there. No electricity hurts modern technology hard.

My guess is that such a world would have similar levels of expertise in biology, less so in chemistry, and certainly less in physics. Fields, such as those used to model light, would be very under-developed. Sure, people would be confused with the wave and particle property of light. However, the concept of fields was not developed until people really studied coulomb forces. There was a point where people though classical physics covered everything. Most of things people discovered which classical could not explained were discovered because they were working on things which practically require metals, such as magnets, vacuums, steam engines, and boring holes in cannons...

There would be no x-rays for your doctor, no radios, no knights in shining armor. A radically different world, but a lot of things would still be developed and known.

Jared Diamond, author of Guns, Germs, and Steel, may argue that we would never have taken off in technological advancement because we lack steel. His theory would put us as a very agrarian society without sufficient metals. This would prevent many other technologies from developing.

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  • $\begingroup$ Why would the concept of fields be under developed? $\endgroup$ – Samuel Mar 5 '15 at 20:03
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    $\begingroup$ Are you only considering the materials required to make an item or also the required infrastructure? Namely the tools used to create nearly every item you listed. If you think semiconductors can be made, then you should include solar panels under electricity generation. $\endgroup$ – Samuel Mar 6 '15 at 0:22
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    $\begingroup$ What about ceramic for steam engines? $\endgroup$ – SJuan76 Mar 6 '15 at 13:13
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    $\begingroup$ @SJuan76 As most ceramics are insulators, I doubt it would work nearly as well as metal for a steam engine. Yes, it can make the chamber, and when it got up to temperature, it would be good, but getting it there would be quite difficult, enough that I said no. $\endgroup$ – PipperChip Mar 6 '15 at 15:44
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    $\begingroup$ @PipperChip - a possible sticking point is how to get to the point of processing aluminum ore efficiently without having other metals to kick start it. It is very (electrical) energy intensive even now. $\endgroup$ – Jon Custer Mar 8 '15 at 16:32
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Luckily this does not entirely depend on mass.

What do we lose?

If there were no Late Heavy Bombardment (LHB) the Earth's crust would be fairly lacking in what are called siderophile elements. This is too bad, there are some good elements in that list, including gold, cobalt, iron, iridium, manganese, molybdenum, nickel, osmium, palladium, platinum, rhenium, rhodium and ruthenium. We'd still have some of these at the surface, we'd just have a lot less of them. The Earth is still bombarded with space rocks, the LHB was just a significant portion of that bombardment over the last four billion years.

It's hard to say how much of what we would have or how the abundance affected abiogenesis or evolution of life. So, we'll assume life still developed in the same way, but we wouldn't have the rich deposits we have now.

So what do we have?

We'd still have lithophile elements and, to a lesser degree, chalcophile elements. Some of the metals we'd get are aluminum, tungsten, and titanium in decent quantity. We'd get a little bit of copper, lead, and tin. It's not a bad start, it gets us through the bronze age. The iron age would be a problem. Because our own timeline would be halted in pre-history it's quite difficult to say where humans would have gone from there.

I find it unlikely we'd figure out the refinement aluminum, tungsten, or titanium without the tools and knowledge developed during our collective experience with iron. Those are difficult metals to refine in comparison to iron.

Technology

The technology we'd be able to develop then would be things we hardly consider technology. Things like spears, hatchets, bowls, and other cooking tools. We'd have wheels and fire. We'd have some woodworking and stoneworking tools. We'd have concrete, but wouldn't have a great method for reinforcement. We'd have glass, though it wouldn't be very high quality.

Again, these are all things that modern people don't usually consider technology. Even though we'd have the elements to make things like microchips, we couldn't develop the required infrastructure.

It'd be a simple world.

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Samuels answer has it right, it isn't that there wouldn't be elements heavier than silicon; there would still be plenty and life would work just fine, but Iron and nickel and gold would be very, very rare, things that we would primarily get from meteorites, rather than mining in the earth.

The idea though that we would have no technology or that technology wouldn't develop is not something that I agree with. Technology develop how it does because it is seen as being the cheapest and best way of doing so at the time it is developing. So things would certainly be very different, but just because things couldn't be how we have it doesn't mean it couldn't be done.

It should be noted that Mesoamerica and the American Southwest didn't really use much in the way of metal except as decoration prior to the Columbian exchange. Which we may look down on, but Atlatl's were able to pierce the armor of the Spaniards, and Obsidian blades are actually sharper than stainless steel http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1273673/ Also, even the point about drills is wrong, as Mesoamerica did artwork with stone which can not be shaped with iron tools, they most likely did abrasive drilling via a bow drill and sand; no bit to wear out at all.

Canals in the US (and in the Maya region during the classic period) actually for a while were able to perform better than the earliest railroads; there would obviously be no iron railroads, and bronze ones wouldn't actually work nearly as well.

Since there is still copper and tin, there actually would be bronze, and there actually could be electronics; and with electronics and electricity comes the lithophile elements such as Aluminium. So some technology could still develop, but how to get there, how it develops, and what it looks like would be very different from what we are used to.

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  • $\begingroup$ Welcome to worldbuilding, nice answer. :) $\endgroup$ – Tim B Mar 5 '15 at 21:55
  • $\begingroup$ Great answer. The point about the technology we have being the result of what was cheapest and best at the time is really important. If all the ingenuity that went into iron and steel research had been directed at glass as the best/cheapest, we would have some simply amazing glass technology right now. $\endgroup$ – AndyD273 Mar 6 '15 at 15:49
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Well considering Phosphorus, Chlorine, Potassium and Calcium just to name a few that we need for our biology, we would certainly be much different. We also use Iron in our blood and Iodine helps with good health.

So to begin, we would likely not be what we are if heavier elements were too scarce.

But we would have had a much harder time without metals to augment our tool building. We would likely have been stuck with a lot of granite tools augmented by glass tools, (including obsidian, volcanic glass)

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    $\begingroup$ That first point, that we need those heavy elements for life, really hurts most of these answers... $\endgroup$ – PipperChip Mar 5 '15 at 19:57
  • $\begingroup$ I am not sure the life needs so much of them. If there was 100x less iron, it would still not hurt complex life too much, would it? $\endgroup$ – Irigi Mar 6 '15 at 17:32
  • $\begingroup$ @Irigi Iron? probably not so much, as long as there was enough of it. However, some of those others might make a bigger issue if reduced by 100x. We might be stuck closer to oceans to keep a healthy diet. One of the reasons we have iodized salt even now. $\endgroup$ – bowlturner Mar 6 '15 at 17:35
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As bowlturner pointed out we use a lot of heavy elements in our own biology, although in trace amounts. I'm honestly doubtful that complex life could evolve at all without anything higher than silicon, but of course I don't know for sure - I'm by no means a biologist.

Assuming it is possible, a species might be able to get away by building things with Carbon Allotropes. They'd need to somehow get to the point where they could change and form those nearly at will, but that could develop over time - they might start with those early if they don't have metals to work with.

Graphene is extremely strong and can be used in place of metals where tensile strength is required (but you can't use it to easily build, say, a wall). Graphite is a conductor and presumably could be used in place of copper. Diamond is a good insulator. That gives you most of the basics to start industrial technology at least.

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The problem would not be the technology itself but the scaling of that technology. With enough iron for small scale experimentation you can still discover electromagnetism - you just can't build entire cities of the stuff.

That doesn't really become an issue until the industrial revolution - before that, metal was rare and expensive anyway.

  • Steam power - a brick boiler should work. Likely larger and heavier than you can build with metal, and probably slower if the attached parts aren't as strong as steel, but it still lets you build factories without needing a direct mechanical connection to a river.

  • Railroads - wood or concrete rails. Keeping them maintained will suck, but the alternative is more expensive than building them from solid gold. Trains are slow and can't carry nearly as much as they do on Earth, but they do better than a horse so it still works.

  • Electricity - Batteries, solar cells and thermopiles can be made without heavier elements. You don't have the option of spinning permanent magnets, but aluminum coils will work well enough.

  • Guns - wooden cannons aren't great, but fortunately the enemy doesn't have access to iron either.

As long as you have plenty of lighter metals like aluminum, you have a suitable direct substitute for iron in most uses - advanced civilization can develop normally. If not, things will be quite different, although not necessarily less advanced. Electricity is still available, but there are no large power stations or high voltage transmission lines. You can have computers running on batteries, but lighting is still gas and factories still use steam engines rather than electric motors. Without cars or very tall buildings, cities would look very different.

Even if most things are possible through direct substitution, there would be a lot of small differences in the technology used. Some things would probably develop earlier - you don't have the simple option of just using iron, so more complex solutions become economically viable. For example, all your armor is made of layered paper, and after a century or so of trying to improve the glue holding it together you end up with something a lot like modern composites, which turns out to make a stronger cannon than the tree trunks your enemy is using...

To take that even further, finding out that most asteroids are made of an incredibly rare and expensive industrial material would be a pretty strong incentive to get into space.

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  • $\begingroup$ Without electricity, aluminium is very hard (time-consuming andf expensive) to refine. $\endgroup$ – Charles Mar 6 '15 at 15:17
  • $\begingroup$ True, though once you have some it becomes easier to generate the electricity you need. Admittedly building that first battery powered aluminum smelter is going to be tricky. $\endgroup$ – Quentin Clarkson Mar 6 '15 at 20:25
  • $\begingroup$ Having copper you can have bronze, and with bronze you can do Steam boilers, guns etc. $\endgroup$ – Jorge Aldo Mar 8 '15 at 19:28

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