[throwup238]

> While composites might seem like a futuristic technology, in many ways, they hark back to millions of years of human and even pre-human material technology. Wood, after all, is the original composite material, as it’s composed of long and short fibers glued together by other substances—much like modern synthetic composites are often made up of carbon fiber held together by epoxy resins. Wood was a chief enabler of the success of our species, and it exhibits many of the advantages and disadvantages of composites.

Not to nitpick too much, but while wood is "technically" a composite material made up of fiber embedded in lignin, I don't think it's very useful to include it under the broad category of composite materials. Engineered woods like plywood and cross-laminated timber definitely are, but it's more useful to classify regular wood as an organic raw material rather than a composite.

The first composite material humans had any experience with was probably silcrete. It's naturally occurring but ancient humans figured out how to strengthen it by heat treating it in a fire (80-160 kYa). The first time humans intentionally made a composite material is adobe/mudbrick (11 kYa), wattle and daub (6 kYa), plywood in Mesopotamia (5.4 kYa), cob (4 kYa), and finally Romans developed something resembling concrete (I dont remember kYa).

[dreamcompiler]

Wood was a chief enabler of the success of our species

Wood was the chief enabler of trees. Trees have to be big, strong, lightweight, and bendable. Homogeneous materials won't work for that application. You need a composite. So evolution invented one.

Even more amazing: Trees 3D print themselves out of carbon dioxide.

[shiroiushi]

>Trees have to be big, strong, lightweight, and bendable. Homogeneous materials won't work for that application.

Why wouldn't titanium work for that application? (Assume that somehow the plant can move nutrients and fluids around some other way.) Or even steel, as long as it's not solid? Obviously, nature can't produce hollow steel tubes, but lots of metals satisfy your requirement list here.

[adrian_b]

In any stellar system like ours, where oxygen is the most abundant element, except for the hydrogen and helium that are contained mostly in the star and in the big planets, almost all metals are completely oxidized (with the exception of the siderophile elements submerged into the cores of the planets, because of their great density) and the amount of metallic substances with a natural origin that can be found in the accessible surface layers of the planets is negligible.

Reducing the oxidized metals requires much more energy than reducing non-metals like carbon, nitrogen and sulfur (which is what the living beings do to make their structural materials), and preventing the reduced metals to spontaneously become oxidized again is very difficult.

This is why no living beings have succeeded to use metallic materials before the humans, and the latter have succeeded to do this only after mastering the fire, which is the other thing that the non-human living beings have not succeeded to do.

There exists a second class of stellar systems, where there is more carbon than oxygen, so almost all oxygen remains bound in carbon oxides, while most other elements are present as carbides, instead of oxides, like in the Solar System. These are much more rare than the stellar systems of the Solar System type and in such stellar systems the chemical composition of the planets would be extremely different from the planets of the Solar System. Because there is no detailed information about such a stellar system (due to their distance), there is very little knowledge about whether there would be conditions in such a system for the appearance of life and how could that evolve. If there is any chance for primitive life forms to use metals in their structures, that would happen only in such stellar systems.

[airstrike]

The only possible way this comment could be more satisfying to read would be if it ended with "Until now." before the camera pans to a strange planet and the movie begins

[adrian_b]

An interesting fact is that while almost all solid objects that exist in the Solar System have their origin in the condensation of gases from which the Solar System has formed, there exist also the so-called pre-solar grains.

The pre-solar grains are microscopic crystals, i.e. particles of dust, which have come to the Solar System as already solid grains of dust, from other stellar systems, typically having been propelled by stellar explosions, e.g. those of supernovae.

Such pre-solar grains have been incorporated in the many small bodies that have been condensed from gases along with the bigger asteroids and planets at the formation of the Solar System.

Some of those small bodies have fallen on Earth as meteorites (the so-called "chondrites"). When such meteorites have been analyzed carefully, pre-solar grains have been recovered. They can usually be easily distinguished from the local objects, by having very different isotopic compositions.

Among the pre-solar grains, there are many that have come from stellar systems of the second kind, with more carbon than oxygen. Such grains, instead of being silicates, i.e. the most frequent minerals in the stellar systems of the Solar type, have chemical compositions that are unusual for the minerals of the planets of the Solar System, like diamond, graphite, silicon carbide or nitride, titanium carbide or nitride, metal grains of either platinum-group metals or iron-group metals, other carbides, nitrides, sulfides, silicides or titanides.

For now, this is the only direct evidence of the second class of stellar systems, beyond the spectroscopic observations of various stars, which provide estimations for the relative abundance of carbon and oxygen in those stellar systems.

While we have some idea about what kind of minerals might be the most abundant in such stellar systems at the time of their initial condensation from gases, I am not aware of any attempt to simulate the possible internal structure for big planets in such stellar systems, in order to determine whether in such planets there could exist some analogs of the volcanism and hydrothermal vents that can provide the energy flux necessary for the appearance of life in the planets of the terrestrial type.

[xp84]

These are two of the coolest and most fascinating comments I’ve read. Idk if you are a professional …. Astrogeologist?? or just a really smart person but I would like to subscribe to your newsletter for sure. Thanks for sharing this!

[djhn]

Is there any high quality sci-fi that explores the second type of solar systems?

[kjkjadksj]

To be fair we are the only creatures to make much use of anything, metal or no. That being said the metals are used by other creatures. Some might eat metal rich mud for nutritional value for example.

[adrian_b]

What those other creatures eat or use are not metals, but chemical substances that contain chemical elements that would have been metals in their pure elemental state.

For instance, many living beings, from bacteria to vertebrates make and use magnetite crystals, for sensing the magnetic field of the Earth.

Magnetite contains iron ions and pure iron is a metal. Nevertheless, magnetite is not a metal, but a ionic crystal, i.e. an insulator. Your blood contains iron and your bones contain calcium, but none of that iron or calcium is in metal form, all are oxidized ions.

There are no living beings that have metallic components. There are a few bacteria that are able to reduce to metallic form the metals that are the easiest to reduce, i.e. gold and silver. However those bacteria do not use in any way the metallic gold or silver that is precipitated outside their bodies by their activity. The reducing of gold and silver is just a defense mechanism for those bacteria, because the ions of gold or silver kill bacteria, and their precipitation when they are reduced removes them from the environment.

As I have said almost all metallic elements present close to the surface of the Earth or of any other planet of this type are oxidized, i.e. they are positive ions that are bound in various ionic substances, like oxides or sulfides, and they can be found inside the bodies of the living beings in the same state as outside (unlike carbon, nitrogen and sulfur, which are oxidized outside, but reduced inside the bodies of the living beings).

Only a few metallic elements are found also as native metals, i.e. copper, silver, gold, mercury and the platinum-group metals. Even for these metallic elements, most of them are far more abundant in oxidized forms (like sulfides or arsenides) than in metallic forms. Only gold is more abundant in metallic form than in oxidized forms, like tellurides (and that is due in good part to the fact that tellurium is also a very rare element, otherwise more gold would be found combined than in metallic form; the gold ions are extremely large, so that they cannot combine well with ions smaller than the telluride ion, like the sulfide ion that combines well with the smaller silver ions).

[bartc]

Trees did not evolve with bountiful access to titanium, but it would be interesting to ponder how they would have evolved on a metal planet

[nakedneuron]

Carbon in the form of carbon dioxide as raw material is literally instantly available and the resulting "composite" is lightweight. This is not to say nature always considers recycling beforehand. Nature needed to invent fungi to break up this carbon dump. Carbon era is named thanks to this fact. And it's tempting to think nature "came up" with humankind to make the humongous carbon dump of the carbon era useful once again.

[digging]

Really, you have causation backward. Eg. the supposed Carboniferous Period was an opportunity for something to evolve which consumes wood. Many "problems" get solved by accident in this way, but many also don't - as long as they take place over a long enough timespan. If they happen too quickly, there's not enough time for living things to adapt.

Currently there is an opportunity for an industrious plastic-eating microbe to hitch a ride in every gut on the planet, deciding the winners and losers of the plastiferous period. All that means, though, is that there's a chance such a creature could appear and take advantage, not that it will happen. (Yes I know plastic-eaters have been discovered, but I'm not aware of any having an effect on the fitness of other creatures.)

[Qwertious]

>but it would be interesting to ponder how they would have evolved on a metal planet

It overlaps a whole lot with the concept of a dyson trees, but the core problem is that it needs to be able to use the metal in the first place - earth is a metal planet, in the sense that ~10% of the planet is iron, and yet our trees are not steel.

[joha4270]

I don't really think that's a fair assessment, since most of it is in the core. That's some very long and heat resistant roots.

I also can't help but wonder, could trees even use iron if it was plentiful in the upper crust? You need a lot of energy to separate iron oxide into elemental iron. Betting against what evolution can make is usually a bad idea, but that would be a neat trick.

[Anotheroneagain]

Both iron and titanium are ubiquitous in the crust. I think they are the 4th and 9th most common elements, and definitely far more common than carbon.

[kevin_thibedeau]

Titanium is more abundant than nickel and New Caledonia's plants have evolved to deal with the latter in unique ways.

[alanbernstein]

I think mainly because trees are not steel plants

[sph]

> Even more amazing: Trees 3D print themselves out of carbon dioxide.

Carbon dioxide and low-entropy energy in the form of solar light.

[slabity]

> Not to nitpick too much, but while wood is "technically" a composite material made up of fiber embedded in lignin, I don't think it's very useful to include it under the broad category of composite materials. Engineered woods like plywood and cross-laminated timber definitely are, but it's more useful to classify regular wood as an organic raw material rather than a composite.

Why would defining it as a raw material be "more useful"? Why is defining it as a composite "less useful"?

[jessriedel]

Yea from a material science perspective, wood seems to obviously be a composite.

[aranchelk]

Not just that. When learning about the anisotropic nature of composites (different strengths in different directions) wood is a tangible example for anyone who’s done arts and crafts, woodworking, etc.

[2four2]

I disagree. In advanced materials, we analyze materials categorically. In this instance, the way we would calculate the structure of wood is based on its isotropy, or more simply, its symmetry of strength and stiffness. The way wood behaves anisotropically means its structure is calculated the same way as most other composites. Composite Laminate Theory is the primary way that structure behavior is calculated for both wood laminates and carbon fiber laminates. We squarely categorize it in the same bin as carbon fiber, but that's just one perspective from one discipline, so take it as you will.

[andrewflnr]

I don't know how I escaped learning about silcrete so far, being interested in both geology and primitive technology. Thanks for the tip! For anyone that curious: https://en.wikipedia.org/wiki/Silcrete

[AYBABTME]

I think it's actually very fair to count wood as a composite. Composite is the concept, and wood happens to be a natural occurrence of the concept. Keeping it qualified as a composite also helps expand the mind: composites don't need to manufactured how we're typically manufacturing it in the present. When you think of wood as a composite, it's an opportunity for ah-ha moments in students.

[marcus_holmes]

> and finally Romans developed something resembling concrete (I dont remember kYa).

About 2 kYa, give or take a couple of centuries.

And it was actual concrete, rather than something resembling concrete. In fact, better than the concrete we were making a hundred years ago, and better than most of our concrete fifty years ago.

Roman aqueducts and bridges are still standing 2000 years later. Not sure I'd put money on the same being true of our stuff.

[tim333]

Yeah there was a theory discussed on HN a couple of years ago that superior qualities came from mixing in quicklime (CaO). I'm not sure if they've developed that and tested it against modern concretes. I guess it's hard to tell if they'll last 2000 years without waiting quite a while. (https://news.ycombinator.com/item?id=34280239)

[marcus_holmes]

I heard it was that they used seawater not freshwater.

And yes, we'll have to wait a while. Though probably not 2000 years - we only have to wait until our concrete starts failing, which might be a lot sooner than that.

[aardvarkr]

I think they’re just trying to make composite more relatable to the Everyman without actually understanding it themselves. At least they’re trying.

[refulgentis]

They're trying, and succeeding, and it's beautiful analogy akin to ones my best physics professors would provide.

[hn_throwaway_99]

Kinda feels like you're missing the point of the quoted sentence. That is, it's not that wood is actually a composite material as we define it now, but that wood has the characteristics of a composite, i.e. different substances intertwined in a way to give better properties than any individual material alone, and going with the theme of the article, this is a direct contrast to materials like steel or plastic.

[jaggederest]

The other important property that wood shares with modern manmade composites is that it is anisotropic - i.e., it is stronger in some directions of force than others. You can use bodyweight to snap a short grain board that would, if it were long grain, hold up under a ton or more.

[fifticon]

note when you make OSB2 and OSB3, you to some degree can make up for this(?)