Wikipedia:Reference desk/Archives/Science/2017 February 5

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

February 5

For how many times the water is dense than air?

In one place I see that the water is "water is about 850 times heavier than air" (I saw it on Wikipedia and some books) and in another place I see that the "air is 784 times less dense than water". What is the truth about the density of the water compared to the density air? 93.126.88.30 (talk) 09:45, 5 February 2017 (UTC)

Well it depends on air pressure, humidity, temperature, and altitude. There are standard conditions where water would be 844.66 times denser (25°). See Density of air which uselessly says "0.0023769 slug/(cu ft)" Graeme Bartlett (talk) 10:03, 5 February 2017 (UTC)

A Slug (mass) is about 14.6 kg. I really wouldn't want to meet a slug with that mass! Dmcq (talk) 10:28, 5 February 2017 (UTC)

That is actually about the weight of the world's largest slug - Aplysia vaccaria Wymspen (talk) 16:04, 5 February 2017 (UTC)

Wow! That really is a HUGE SLUG! I'm not certain I'm all that reassured by it being herbivorous :-) Thanks very much. Dmcq (talk) 17:15, 5 February 2017 (UTC)

• Minor nitpick: it depends only on composition, pressure and temperature; altitude does not directly matter, although of course it will change pressure (a lot), temperature (slightly) and humidity (I guess?), so density will be impacted by a change of altitude. Tigraan^{Click here to contact me} 12:18, 5 February 2017 (UTC)

Altitude matters greatly. At the top of Mt. Everest (8,848 metres or 29,029 ft above sea level) the air is about a third as dense as at sea level, while liquid water density is almost invariant. Blooteuth (talk) 16:37, 5 February 2017 (UTC)

Blooteuth misinterprets Tigraan, but really you both agree. This big effect of altitude is mostly because of the effect of pressure, with an influence also of temperature and humidity, all 3 of which tend to covary with altitude. But if you keep pressure, temperature and humidity constant (e.g. in an aeroplane), the altitude itself indeed has no direct effect on their densities relative to each other.Jmchutchinson (talk) 17:04, 5 February 2017 (UTC)

Precisely so. As an aside many people assume that moist air (i.e., containing water vapor) is more dense than dry air, when in fact it is the opposite. Shock Brigade Harvester Boris (talk) 17:45, 5 February 2017 (UTC)

On this point: Often wondered about whether a hot air balloon get most of it buoyancy by the hot air or the water vapour produced by burning the LPG. OK some might say but what about the combustion products containing heavy CO₂. Answer, The balloon already is carrying the carbon fuel. The atmospheric oxygen which gets combined with the hydrogen in the fuel (water vapour) surly provides more lift than lesser density which the hot air alone can provide. --Aspro (talk) 22:16, 5 February 2017 (UTC)

Interesting. I could turn this into a homework problem for my PBL course. You'd have to make some assumptions about how much ambient air gets entrained into the burner exhaust, etc. Shock Brigade Harvester Boris (talk) 22:22, 5 February 2017 (UTC)

Would be delighted if this can be incorporated into a PBL because at my age I can't be bothered to get my slide-rule out and do it myself. Hot air balloons are normally fueled by butane C₄H₁₀. Perfect combusted that gives the maximum amount of water vapor can easily be calculated but in reality combustion is seldom complete, so that is one unknown. Yet look at the sums, the burner is producing a lot of water vapor.--Aspro (talk) 23:13, 5 February 2017 (UTC)

Slide rule? And my kids think I'm a luddite... Shock Brigade Harvester Boris (talk) 23:53, 5 February 2017 (UTC)

Welcome to the club of luddites ;¬) But when the latest microsoft update crashes their computer or the batteries run down in their smart-phones/tablet/iPads (or whatever modern gizzomo that thet can't live without) who's going to be laughing then?!! --Aspro (talk) 22:47, 6 February 2017 (UTC)

Instead of calling it a slide rule, call it by the alternate name we used to use: "slipstick". That sounds niftier. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:12, 8 February 2017 (UTC)

If it depends on a lot of factors, then why is it written so simply (that the density of the water is 850 times than the air) in many books, articles and on Wikipedia? I don't understand this issue why all of those sources chose this number while it depends on a lot of factors.93.126.88.30 (talk) 23:13, 5 February 2017 (UTC)

For most purposes such a value is enough. Another similar assertion is that "water boils at 100°C", which is only true for sea-level pressure on Earth, but good enough to remember as a rule of thumb; yet, scientists studying e.g. water on Mars need to know that it is not true. It is similar to a Wittgenstein's ladder: it is false, but not false enough to be preferable to complete ignorance. Tigraan^{Click here to contact me} 09:57, 6 February 2017 (UTC)

So the 850 times is the normal case? What is the normal case? Sorry I'm a little bit confused:) 93.126.88.30 (talk) 15:08, 7 February 2017 (UTC)

There is not really any "normal" but there are "Standard conditions for temperature and pressure" which it seems you can choose from, but I like the standard state of 25°C and 100000 pascals. The U.S. Standard Atmosphere assumes the air is perfectly dry, and so is unrealistic. Graeme Bartlett (talk) 22:49, 7 February 2017 (UTC)

hand sanitizer

Does normal drinking alcohol kill bacteria and fungi as well as the special hand sanitizer stuff does? If I used Smirnoff 90% Proof Vodka to wash my hands would it be as effective as Purell? — Preceding unsigned comment added by 83.239.58.162 (talk) 18:45, 5 February 2017 (UTC)

The alcohol is generally the same in both substances — it's ethanol either way. However, 90 proof is only 45% alcohol, and according to the FDA, 60-95% alcohol is required for optimum anti-microbial properties in hand sanitizer, so you'd want something more like Bacardi 151 to be on the safe side. Also, that's some very expensively distilled and aged EtOH to use for hand sanitizer ;) NorthBySouthBaranof (talk) 18:56, 5 February 2017 (UTC)

You may find this of interest. Richerman (talk) 23:18, 5 February 2017 (UTC)

While some sanitizers use isopropanol (including many hospital pads), which is more toxic, it is also often used at similar concentrations (I commonly see 70%). However, isopropyl alcohol is much more dangerous if ingested. It should also be noted that in various countries, ethanol products which are not destined as beverage are usually denatured, also making them more of a health hazard if consumed. This allows to bypass alcohol taxation, and at the same time discourages the drinking of products which may already otherwise contain ingredients not considered safe to drink. 76.10.128.192 (talk) 11:32, 8 February 2017 (UTC)

Had Abiogenesis Happened Once?

Life can originate from the non-living matter at any time simultaneously and constantly at local, regional depend upon the watershed, continental and global level if appropriate environmental condition available. This means there are possibilities that many different types of life can be arisen all over the earth instead of one type (known established form). Thus if abiogenesis can happen more than once then why we don’t see today

1- the existence of other types of life

2-disappearing transitional species/individual fully or partially developed tissues, organs, systems, and organisms in the process of evolution of the current known established form of life.2001:56A:7399:1200:D99:A16F:40C0:C96A (talk) 22:36, 5 February 2017 (UTC)EEK

Life arose under conditions very different from those that exist today. In particular there was virtually no oxygen (O2) in the atmosphere. Oxygen is necessary for many current forms of life, but it probably would have been very destructive to the earliest forms. There were other major chemical differences as well. Looie496 (talk) 22:49, 5 February 2017 (UTC)

You will find the answer to the second part of your question about transitional species here. As they say, all species are transitional as evolution is a continuos process that never ends, but the ones that are most obviously in the process of changing are the flying squirrels, walking catfish and the leaping blenny - a legless, leaping fish that lives on land. Richerman (talk) 23:56, 5 February 2017 (UTC)

Abiogenisis could have, and maybe did, happen more than once on Earth, but it didn't necessarily happen very often. It may not have happened on Earth at all, if theories of Panspermia are correct.

Once it had happened (or arrived) once, the non-living chemical raw materials for it happening again would quite likely be sources of food for the already-existing live organisms, so the chances of it happening a second time would have been reduced.

Similarly, any second, third, etc., forms of life to arise through abiogenisis (if they did) would also be likely "prey" for the form that had arisen first and had a head start on evolution.

We think life first arose around 3.8–4.1 billion years ago, but for the first 3.0–3.3 billion years it was only single celled (and to begin with may not even have had cells): such organisms do not form easily recognised fossils, and when they do they're difficult to analyse in terms of their biochemistry, so the evidence for any of them being from a second, third, etc., abiogenetic formation would be very difficult to identify even if they were, although other Hypothetical types of biochemistry have been considered.

If any organisms from an independant abiogenetic origin were alive today we would probably be able to tell from examining their biochemistry. The fact that we have been looking hard but have found none so far suggests that they are not being formed very often, if at all, today. However, the existence of an as-yet-unidentified Shadow biosphere is not impossible. {The poster formerly known as 87.81.230.195} 94.12.94.189 (talk) 02:30, 6 February 2017 (UTC)

• A modern spontaneous abiogenesis is unlikely because life is already ubiquitous, and most ecological niches are already filled by organisms that have had millions of years adapting to their conditions. Any new "cell" would likely find itself simply a convenient morsel for a more advanced heterotroph. μηδείς (talk) 02:34, 6 February 2017 (UTC)

• One possibility is that multiple abiogenesis events occurred, and some of the branches died out entirely, while others merged into current life forms. For example, the mitochondria in each of our cells has it's own genetics and reproduces independently, making it a possible separate life form that was incorporated into animal cells billions of years ago (this is just one possibility). StuRat (talk) 03:43, 6 February 2017 (UTC)

Biologists now have no doubts about the endosymbiotic origins of mitochondria from bacteria. However, they and the eukaryote host share many homologies (e.g. most of the genetic code converting nucleic acid sequences to peptides), so they (and indeed all other organisms that we know) are unambiguously NOT descendants of separate abiogenesis events. Endosymbiosis can at most be only crudely analogous of possible early symbiosis between the products of different abiogenis events. But competitive and predatory interactions seem likely to be much more predominant processes.Jmchutchinson (talk) 07:37, 6 February 2017 (UTC)

Agreed, but the evidence that one organism was incorporated into another does make it possible that two organisms from separate abiogenesis events could also have merged, probably very early in the history of life on Earth, as later "more evolved" organisms would be less likely to benefit from such a merger. StuRat (talk) 16:04, 7 February 2017 (UTC)

I may be wrong but it seems all living things are earthly due to lack of exotic element component in their bodies. Both the earth and ocean have not yet explored fully or unseen by human eye. The rest of world did not know America before 1492 so imagine the only slow mode of transportation existed was the natural land, air, water. This means the pockets of other forms of life either well settled or incomplete or early transitional species e.g. partially or fully developed tissues, organs, systems, and organisms in the process of evolution of known life may still exist or at least their impression if not completely perished by the well-established life. 2001:56A:7399:1200:F41F:EAAF:2DAB:EA49 (talk) 04:18, 6 February 2017 (UTC)EEK

You seem to have your terms all confused. Abiogenesis is simply a random assortment of chemicals happening to form the basic building blocks of life.

Abiogenesis has nothing to do with hypothetical partially developed organs. At no point where there detached spleens and free livers floating in the oceans, much as Young Earth creationists love that strawman. Eyes did not just evolve in isolation, they evolved as parts of lifeforms. Imagine a bunch of blind critters. Now, bear in mind that any creature can detect heat, which is a form of radiation, as is light. Imagine that one of the blind critters, thanks to a mutation was born with a small group of nerves able to detect light in addition to heat (like in the first part of the picture in the Evolution of the eye article). It would be better able to evade hazards as well as find food than the completely blind critters. Maybe not by much, but over many many generations it would make a serious difference. This pushes otherwise random Genetic drift until you eventually have, for the most part, critters able to tell if things are light or dark, but not necessarily the direction of said lightness and darkness. Once again, if some mutant critter is born that is able to discern the direction of light (like in the second and third pictures of the Evolution of the eye article), they would be better able to evade hazards and find food. In time, those critters with those proto-eyes would be pretty common. It's the same for the rest of the stages in the Evolution of the eye article.

Now, if you were talking about whether the "same" organ can appear multiple times (for example, some other creature unrelated to the first critter to evolve a proto-eye develops similar photoreceptive patches and starts the same chain again), that's still has nothing to do with abiogenesis. That would be Parallel evolution, which can happen.

If you are asking if we do not know for sure whether abiogenesis has occurred a second time in some part of the planet we cannot yet explore, considering that part of the reason we cannot explore those parts of the planet is that they are hostile to life, Occam's razor would have us side with "no." If you are asking if we have missed something in some part of the planet we could explore but have just missed so far -- how are we supposed to know? It is unknown, by the possible definition of your rather vague and rambling question. It would be more reasonable for me to ask you if you personally know for certain if the closest town you've never visited has a coffee shop staffed by five redheaded lesbians -- because there is the possibility that someone could ascertain that information at this moment. Ian.thomson (talk) 08:29, 6 February 2017 (UTC)

I suspect that abiogenesis, like speciation, tends to blur out if you look at it closely. We know that when species are separating there are periods when there is a broad population with subspecies and different populations with gradually increasing levels of reproductive isolation. Similarly, with abiogenesis, I assume that a close look at the beginning would leave you scratching your head trying to decide which molecules are "alive" and which are "dead", and what the boundaries of an "organism" are. Different chemical phenomena would appear to be abiogenesis-like phenomena and some would work out alliances while others would not. For example, some models of abiogenesis imagine that cell membranes arose spontaneously, and others describe an RNA world; some even talk about random proteins arising from polymerized hydrogen cyanide. These could be true and false hypotheses or they could be rival "origins of life" that all became one thing.

I am fond to think of bits of RNA tethered to a phosphate-bearing rock, including unusual nucleotides now reflected in enzyme cofactors of ancient origin, and becoming a symbiotic community, each "gene" having its place in some sort of "ecosystem" of the naked nucleic acid on the surface, whether to replicate itself and others or collect nutrients i.e. chemicals or to hold them and pass them around. There would be many copies (with poor fidelity, perhaps) of each gene, and many different activities, some beneficial, some even perhaps harmful, not all replicative. Without a cell membrane in sight, how do you say how many organisms that is, where its boundaries are, which parts of it are alive and which parts are dead, and which fundamental phenomena within it were "abiogenesis" and which were "evolution" and which were just chance?

In a sense, abiogenesis could happen today. Suppose a bacterium develops the ability to degrade a certain plastic into fatty acids. Evolution favors its spread. After a while the plastic falls out of favor and becomes scarce, but the enzyme is reversible, and the bacterium finds that secreting the plastic helps it to stick to PVC pipes and serves as a stored energy reserve its competitors can't digest. Well, looked at a certain way, you can say that an abiogenic process (i.e. some bright engineer) invented the plastic, and now the plastic has developed the ability to grow and reproduce and permanently plug up your sewage pipes. Wnt (talk) 14:44, 6 February 2017 (UTC)

• That all surviving life on Earth shares one common ancestor is proven by the fact that the genetic code is arbitrary. That is, there is no chemical necessity (from the shape of the molecules) which requires that certain DNA or RNA molecules in ribosomes code for which amino acids. The ribosomal units which tell which amino acid to add next to a protein being produced are made up of long molecules. The part of the molecule which reads the three letter RNA codon indicating which specific amino acid to grab is not close to and does not by chemical means physically determine which of the 20 or so amino acids will be attached to the growing protein string.

In other words, the part that reads the instructions is distant from and different from the part of the ribosome that builds the protein. The code is highly conserved as of necessity--otherwise the whole system will break down. But which three RNA molecules are associated to which amino acids is just a matter of chance, and the chances of a similar code arising by chance in two separate lineages is astronomically small, to the point of impossibility. μηδείς (talk) 17:02, 6 February 2017 (UTC)

It's worth noting that the genetic code is not as highly conserved as we were all taught in high school. There is some degree of variation, especially when examining mitochondrial genetic codes. Additionally, I wouldn't discount the role of horizontal gene transfer in introducing some potential for ubiquity despite variations in ancestry, though that is a bit of speculation on my part. --OuroborosCobra (talk) 17:58, 6 February 2017 (UTC)

Not as well preserved in this case means that some basal branches differ from the eukaryotes in the coding for one or two amino acids or use different acids. It's like saying that some poker decks come with jokers, not that some organisms play pinochle while others play mahjong. Statistically, the chances of convergence rather than common origin are nil. μηδείς (talk) 22:31, 6 February 2017 (UTC)

Proving we have a common ancestor does not prove it was the sole ancestor. Just as we found out eukaryotes incorporated endosymbionts, it is possible that various other abiogenetic origins of life led to organisms which now are integrated into our biology - such as cell membranes. We also should not forget that in the modern age of molecular biology, we tend to define life as stuff with DNA, and usually as DNA we can pull out with PCR. There is little real proof that some weird thing like desert varnish doesn't contain some entirely other kind of interesting, self-replicating biochemistry that we can't recognize because it doesn't contain anything at all familiar to us from "living" organisms. Wnt (talk) 23:48, 6 February 2017 (UTC)

Thanks all for your interest and replies. Although my knowledge of the evolution is very very slight but the cause of evolution is abiogenesis. No abiogenesis means no evolution. An organ doesn’t necessarily mean its kidney eye heart etc. It could be any undefined individual living thing say organ that we can imagine only which could have evolved partially or fully w.r.t (reactive) to its surrounding environment. 2001:56A:7399:1200:60C0:BCDD:A7F:24F2 (talk) 20:10, 6 February 2017 (UTC)EEK

You are not using the words organ or evolution above, IP 2001, to indicate the same evidence-based concepts scientists do, and there is no claim that RNA-based life did not arise at least once or that there were not other unimagined early self-repicating processes. There is simply evidence beyond a reasonable doubt for the common origin of all extant life. This is like saying that we know all birds alive had a common ancestor, it doesn't make any claim against long-dead organisms of which we have no evidence. μηδείς (talk) 22:31, 6 February 2017 (UTC)

Abiogenesis is not the cause of evolution, because the general principle of evolution preceded living organisms. It is a general principle by which the world works. For example, if you toss trash into a burn barrel (I know, a very backward thing to do, but it happens more often than is commonly imagined!) you'll end up with an accumulation of fireproof trash at the bottom, by a process of selection. If a hillside erodes, eventually there will be hills of resistant rock. I would suggest it is also at least technically possible that it was not even the cause of life. We can't yet completely rule out panspermia, though the space agencies are working on it - and while that may seem only to create a chicken and egg problem, if there is such a thing as panspermia we must take into account the possibility that life evolved in some gradual way from forms of life living in much hotter conditions in the early universe. It's at least conceivable that some kind of evolution links our life, continually adapting to ever colder and slower living conditions, all the way back to some kind of complex phenomenon of nuclei self-organizing in the quark-gluon plasma that filled the early cosmos... and going back even further, we see only more and more complex physics, which might have provided opportunities for life on an ever faster timescale the closer you come to the beginning. Now that seems almost infinitely improbable, but I don't think anyone knows or can know it's false, unless they can rule panspermia false, because beyond that the trail is far too convoluted to track. Wnt (talk) 00:00, 7 February 2017 (UTC)

The problem, Wnt, is that you are suggesting alternative causes with no evidence whatsoever. It makes me wonder if you were an adult when OJ's defense team suggested, with no evidence whatsoever, that his wife and Ron Goldman had actually been killed by Colombian druglords. That is what is called a positive defense and it requires that evidence be provided.

Since no such evidence was provided, Judge Ito was incompetent. He should have declared the "defense" invalid. Unless you have actual evidence of some earlier ancestors, there is simply no reason to grant your speculation the respect worthy of a wild speculation. Your speculation is beyond wild, it is entirely baseless. μηδείς (talk) 03:54, 7 February 2017 (UTC)

I don't think it is unreasonable to suggest an improbable alternative (as I admitted) to show that a theory is not a logical necessity. We have too many sidetracks open for me to argue here about how tightly a defendant should be muzzled while he is being condemned. Wnt (talk) 12:08, 7 February 2017 (UTC)

What we know about abiogenesis suggests, at least to me, that it requires conditions very far from thermal equilibrium, it cannot happen at any of the ambient conditions the Earth was in. To get to very complex molecular machines when the smaller parts would not be functional requires conditions where you can get a wild card for not getting things right, and that suggest that very low temperatures where you can freeze a system into a far from equilibrium state (we call this metastability) could have played a role. Take e.g. a comet in an elliptic orbit that brings it close to the Sun during part of its orbit. During the time it's far from the Sun you can have chemistry going on that's different from when its close to the Sun, together they can complete some catalytic cycle but it could be that there doesn't exist a single ambient environment where all parts of the cycle can be completed. So, in the beginning you could have had self-replicating cycles that take an entire orbit of the comet to complete, and the fact that far from the Sun some fragile molecules are protected from decay could have played role. Life in compartmentalized forms inside cells would have arisen later, when you get a self replicating cycle started, you'll get exponential growth which leads to evolution as explained here and here. Count Iblis (talk) 04:34, 7 February 2017 (UTC)

I may be misunderstanding you, Count Iblis, when you say ". . . abiogenesis requires conditions very far from thermal equilibrium . . . it cannot happen at any of the ambient conditions the Earth was in . . . ."

But abiogenisis is not theorised to have occurred everywhere at once on an Earth in overall thermal equilibrium. Within that overall stable state there have always been particular places where the local thermal conditions were not in equilibrium. Ambient sunlight always causes local thermal gradients, as do volcanic processes. In any case, sheer thermal inequalities are not generally considered sufficient in themselves; most researchers in the field seem to focus on chemical/ionic inequalities, often arising from various geological conditions, from which pre-living and subsequently living (bio)chemical processes could gain energy. {The poster formerly known as 87.81.230.195} 94.12.94.189 (talk) 22:26, 7 February 2017 (UTC)

Yes, I agree with this, but I think (just my personal opinion) that the research that is being done to simulate biochemistry that can take place inside comets is more likely to yield success. Count Iblis (talk) 04:06, 8 February 2017 (UTC)

@Count Iblis: I'm going to join the anal-retentives this time and say you must cite this. No, not because "this is a reference desk" but because this is a cock-tease! ;) Wnt (talk) 23:35, 8 February 2017 (UTC)

The possibility was mentioned in an NGC documentary and there are some research results like formation of ribose from water methanol and ammonia. But it's mostly based on my personal opinion having read some review articles about the outstanding problems that the natural solution is to consider a comet or a proto-planet within which you have a diverse set of local conditions that are mutually far from thermal equilibrium and you can also have predictable changes due to an elliptic orbit. There is much more potential to get life started there than on an Earth-like planet. Compare this to heating your house without using any fuel. If you want to keep your house at 20 C and it's 15 C outside and everywhere outside it's 15 C then this is an impossible task. A heat pump will still need a source of work to pump heat from 15 C to 20 C. It's much easier to keep a house heated at 20 C without fuel in Antarctica in the polar Winter when it's -70 C outside by making use of the fact that at some depth the ice is at -50 C. This allows you to run a Sterling engine, you can then pump heat from -50 C to your house at 20 C to keep it warm. Count Iblis (talk) 01:23, 10 February 2017 (UTC)

concrete roads

I was reading this article[1] and noticed that they don't mention concrete roads. I see a lot of the new infrastructure using concrete roads instead of asphalt.

Could the decline of asphalt usage be explained by its obsolescence and ongoing replacement with concrete roads? ECS LIVA Z (talk) 20:39, 5 February 2017 (UTC)

According to the article, it's about money. Your average country road is asphalt, but if there's not enough money to do right by those roads, then less asphalt is purchased. Interstates, in contrast, are usually concrete. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:11, 6 February 2017 (UTC)

Were interstates ever usually asphalt? Sagittarian Milky Way (talk) 04:47, 6 February 2017 (UTC)

To my recollection, they were always concrete. But the federal government is paying for a good chunk of it. Not so with the country two-lanes. Interstate Highway standards doesn't seem to say anything about materials. But there's at least one illustration of an interstate overlaid with asphalt. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:24, 6 February 2017 (UTC)

Here's a comment on why concrete is generally used for the interstates.[2] ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:31, 6 February 2017 (UTC)

Asphalt doesn't seem obsolete to me. Obligatory link: road surface. Interestingly, that article says: An asphalt concrete surface will generally be constructed for high-volume primary highways having an average annual daily traffic load greater than 1200 vehicles per day.[5] To me, high volume means 1200 vehicles per hour (although not the entire day).

It must be a regional thing. I've seen only few concrete roads in Europe: some mostly larger roads in Germany, a few in Belgium (mostly smaller country roads) and some bus lanes and cycling paths in the Netherlands, although the latter are being replaced by asphalt. Which kind of surface is used depends on many factors: money, summer heat, freeze-thaw cycles, noise, drainage, driver comfort, traffic characteristics, tree root resistance. PiusImpavidus (talk) 11:11, 6 February 2017 (UTC)

• Interstate Highway design standards are available publicly. here is the 2005 edition of the document. It does not specify what the paving material must be, merely that the road be paved. Individual states are left to their own devices to decide what to pave the roads with. Some use asphalt, some use concrete. --Jayron32 15:24, 6 February 2017 (UTC)

Cobblestones? Sagittarian Milky Way (talk) 16:09, 6 February 2017 (UTC)

Cobblestone is used in Massachusetts in exit gores. This page shows a picture of one on I-290 in the Worcester area. It is not used a paving surface for high speed travel, because even in Massachusetts, the road designers are not sadistic or stupid. --Jayron32 21:03, 6 February 2017 (UTC)

• Also see here. According to that document, 60% of the interstate system is paved with concrete, which means 40% is asphalt. --Jayron32 15:28, 6 February 2017 (UTC)

Also, see Chipseal, which in the USA is apparently mostly used for rural (low traffic density) roads. Here in New Zealand, chipseal is used extensively in urban side streets and in some arterial routes, despite being much noisier than asphalt. Several roads in Auckland were constructed in concrete during the 1920s and 30s, but concrete construction was abandoned soon after. Virtually all have been paved over with asphalt. See here for details. I'd be interested in more references; that is the only one I've been able to find. Akld guy (talk) 20:31, 6 February 2017 (UTC)