Science desk
< July 29	<< Jun \| July \| Aug >>	July 31 >

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.

July 30

Is the average unpalatability of the plant kingdom (not counting parts the plant wants eaten) increasing over time?

Some have evolved thorns, needles (i.e. pumpkin stems), itching chemicals, poison etc. to discourage being eaten. Nonetheless this is far from universal. Are the undefended species mostly ones where resources are more effectively used for other things like "more seeds" or are they mostly "herbivore defense mutation hasn't happened yet"? If the latter then it seems plausible that if evolution were allowed to proceed for hundreds of millions of more years without human interference then there should be more biomass with anti-herbivore/omnivore defenses by then. Maybe even a reduction in the amount of far-apart, not that sharp thorns in favor of closer-spaced sharper ones. Sagittarian Milky Way (talk) 19:33, 30 July 2018 (UTC)[reply]

Your proposition assumes that plants would evolve while herbivore animals would not; however, "unpalatability" is a moving feast: see Coevolution. {The poster formerly known as 87.81.230.195} 90.217.102.16 (talk) 20:05, 30 July 2018 (UTC)[reply]

Is defense getting better then? And offense too of course (poison resistance, tougher mouths etc.) Sagittarian Milky Way (talk) 20:19, 30 July 2018 (UTC)[reply]

Err . . . yes, but so is attack. Did you not read Coevolution#Predators and prey? OK, try Evolutionary arms race. All this is Evolution 101. {The poster formerly known as 87.81.230.195} 90.217.102.16 (talk) 22:52, 30 July 2018 (UTC)[reply]

If I see 300 million AD and every plant is covered in glass fur I'd still consider defense increased even if it makes no difference in relative terms (the evolutionary arms race). Would be interesting to see what can eat that though. Sagittarian Milky Way (talk) 23:39, 30 July 2018 (UTC)[reply]

Herbivory is not the only selection pressure that operates on plants. Plants compete with each other, and other organisms, for access to resources. They also have to withstand attack by fungi and microbes. Defenses against any of these are not free to the plant, and thus plants' phenotypes will change over time based on the balance between different selection pressures. Of course this works the other way around too! You can probably find at a nearby grocery store fruits produced for consumption by animals that no longer exist. They only haven't gone extinct because the plant got lucky and was "adopted" by humans, who can propagate the plant without eating the seeds.

There's not really any objective way to quantify "more" or "less palatable". Thorns might make you less inclined to eat a plant, but they make little difference to giraffes, which have thick tissue covering their palates for consuming thorny plants, or to insects crawling around on the plant. There is no "ultimate goal" evolution is working towards, so saying "herbivore defense mutation hasn't happened yet" doesn't make sense. --47.146.63.87 (talk) 03:58, 31 July 2018 (UTC)[reply]

The avocado thing is interesting. Here's an article though that talks about it ... the article also says that there are wild avocados that wouldn't be recognized as edible, which have apparently survived the 13,000 years since extinction of megafauna. They make a bunch of handwavey arguments about jaguars and rodents without AFAICT any proof. It sounds like the theory is perhaps not altogether complete... Wnt (talk) 14:19, 1 August 2018 (UTC)[reply]

So why don't say maple leaf stems have thorns or noxious chemicals like poison? Has it been tried but other maples were more successful and it never caught on or is it more likely that a thorny maple hasn't existed yet? (("thorn mutation never happened" (in that species)). I've heard THC was invented to be sunscreen. This was useful and cheap enough to catch on (to wild THC percents, not the extreme THC percents of modern breeding of course). But neighboring plants that can't reproduce with cannabis don't have it so it seems like useful mutations can just be too rare to have happened by 2018 AD. If so then it'd stand to reason that there's species that would probably select for THC or poison or thorns or whatever if only that mutation would happen and give it a few hundred million more years of uninterfered with evolution and some of these mutations that'd be selected for but haven't happened yet would happen and spread right? Sagittarian Milky Way (talk) 06:55, 31 July 2018 (UTC)[reply]

It takes energy to make thorns or poisonous substances. And there are different protective mechanisms, eg attracting animals like ants that may defend the plant, hard impenetrable bark. Also thorns will not stop small herbivores like caterpillars or beetles. Dumping all the leaves every year also will disrupt the animals that depend on eating them. Some weeds will just grow and flower very fast. Graeme Bartlett (talk) 07:54, 31 July 2018 (UTC)[reply]

Chemical elements and the next, nearest one

I'm just completing my knowledge of chemistry and need to ask one last thing:

When an element, say gold, becomes gold, does it become gold from an adjacent element on the periodic table, because it got an extra bit, or lost an extra bit? A yes or no is fine, if you like.

Many thanks,

Anna Frodesiak (talk) 21:28, 30 July 2018 (UTC)[reply]

In general, both are possible. For example, through:

Alpha decay in which the element's atomic number decreases by two (and mass number by four)
Beta decay in which the element's atomic number increases by one (mass number remains constant).

For gold in particular, see Synthesis of precious metals#Gold. Some rare isotopes of platinum, thallium etc, do decay into gold naturally, too. Abecedare (talk) 21:43, 30 July 2018 (UTC)[reply]

Thanks, Abecedare. Ah, so gold can come into existence from thallium without mercury ever being involved, right? Anna Frodesiak (talk) 21:51, 30 July 2018 (UTC)[reply]

Yes. For example, ¹⁸¹Tl alpha decays into ¹⁷⁷Au (which itself is unstable and will soon decay into isotopes of platinum or iridium). Abecedare (talk) 22:02, 30 July 2018 (UTC)[reply]

Looking at the wonderful chart at [1], which, be warned, is going to simply vomit tremendous amounts of information at you... I see that the one stable isotope of gold, ¹⁹⁷Au, can be arrived at from beta decay of ¹⁹⁷Pt, and electron capture from ¹⁹⁷Hg. There are many unstable isotopes of gold that are themselves parts of other decay chains. As you can see at Isotopes of thallium, a number of thallium isotopes can decay by alpha emission directly into gold, but all of these yield unstable isotopes that then further decay into something else. Someguy1221 (talk) 21:58, 30 July 2018 (UTC)[reply]

You two have answered my question indeed. And wow, that link is really quite something. Thank you both. Anna Frodesiak (talk) 22:08, 30 July 2018 (UTC)[reply]

Gold atoms are from supernovas. Not every last gold atom of course. Supernovas are hot enough to turn materials no heavier than iron-56 into gold-179 and even uranium-238 I think. They make the centers of stars look like freezers. Sagittarian Milky Way (talk) 23:50, 30 July 2018 (UTC)[reply]

In our supernova nucleosynthesis article, there is a chart [2] that shows the origins of each element. It indicates that most gold is produced by neutron star mergers, with a small amount from dying low mass stars. It doesn't appear that any significant amount of gold comes from supernovae. CodeTalker (talk) 00:54, 31 July 2018 (UTC)[reply]

Exactly how much of the r-process yield we see comes from supernovae and how much comes from merging neutron stars is still under discussion according to the article; certainly until recently the major site of the r-process was thought to be supernovae. The yield from low-mass stars is from the s-process. Basically, most isotopes of heavy elements can be produced in two ways, both of which involve neutron capture. One way is the s-process (s for slow neutron capture); there a seed nucleus (iron if you like) slowly captures neutrons one at a time. After a few it gets a neutron excess and becomes unstable to beta decay, a neutron converts to a proton, and we have the next element. The other way is the r-process (r for rapid neutron capture), where the seed nuclei are spammed so quickly by neutrons and they have no time to beta decay until the neutron drip line (the point at which a nucleus will not capture and retain another neutron, as its binding energy would be zero). The r-process tends to produce more neutron-rich stable nuclides and the s-process tends to produce the ones closer to the middle (there are also a few proton-rich stable nuclides called p-nuclei whose origin is still a little mysterious), but many nuclides (like gold-197) can be produced both ways. Only for the very heaviest elements (thorium and uranium) does the r-process alone contribute, because the elements between bismuth (83) and thorium (90) are very unstable, and the s-process does not spam neutrons fast enough to cross this gap; that is why thorium and uranium are quite rare in the Universe (qnd what does get produced slowly decays away). Double sharp (talk) 01:33, 31 July 2018 (UTC)[reply]

I do not see supernovas in that chart. Anna Frodesiak (talk) 03:54, 31 July 2018 (UTC)[reply]

Exploding massive stars are supernovas. Graeme Bartlett (talk) 07:49, 31 July 2018 (UTC)[reply]

Ohhhhhhhhhhhh, really?...of course I knew that. :) Anna Frodesiak (talk) 10:27, 31 July 2018 (UTC)[reply]

Wikipedia has an article titled supernova that can help you learn more about the subject, especially stuff that you hadn't already known. --Jayron 32 15:13, 31 July 2018 (UTC)[reply]

Trying to give a more general answer without too much jargon. Helium is produced by fusing protons (in other words, hydrogen-1 nuclei) together. Some of the protons then change to neutrons. Most helium was produced this way in at the beginning of the universe. Stars produce more helium by the same mechanism. The majority of elements after that up to nickel are produced in stars by more fusion, which successively adds alpha particles, a.k.a. helium-4 nuclei. This means protons get added two at a time, which is partially why elements with even atomic numbers are more common than odd. The elements after nickel are, as others have expounded on, mostly made from bombardment of nuclei by various particles, most often neutrons. This occurs in a variety of processes, such as supernovas. See the nucleosynthesis article for all the gory details. These processes occur much less often, and fusion of elements after nickel uses up energy instead of releasing it, so these elements are much rarer. Also, when radioactive nuclides are produced, they eventually decay, which (usually) changes them into other elements. Quite a few nuclides are only produced (at least in nature) by this mechanism. As also discussed above, the products depend on the parent nuclide and type of decay. --47.146.63.87 (talk) 07:33, 1 August 2018 (UTC)[reply]

How is the optical effect called when you laquer carbon fiber?

How is the effect called when someone laquers carbon. i jknow in wood it means chayotance but i never find anything related to carbon. i can only find depth effect but i think not that this is the right word to use. — Preceding unsigned comment added by Saludacymbals (talk • contribs) 21:32, 30 July 2018 (UTC)[reply]

See the article Chatoyancy that describes the reflectance effect in gemstones and treated wood surfaces. Chatoyant carbon fiber is advertised, see video., and has been used in knife handles, see video. DroneB (talk) 23:57, 30 July 2018 (UTC)[reply]

thats the wrong answer..i meant when carbon fiber is laquered several times the structure has a 3 dimensional effect and i dont know the right word for it

Saludacymbals, please sign your posts by affixing "~~~~" at the end of your message. As to your question, I think you missed Drone's implied answer, which as far as I can tell is the correct one: the name for the optical effect when applied to lacquered carbon remains "chatoyancy" and the adjectival description of the item possessing this quality remains "chatoyant"; this is not altogether surprising given that the term is already applied to a variety of different materials already as diverse as wood and minerals. Snow ^{let's rap} 18:09, 6 August 2018 (UTC)[reply]