Wikipedia:Reference desk/Archives/Science/2008 December 21

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.

December 21

Hey, have they ever expanded on that life creating experiment thing?

I mean well beyond the Miller Urey experiment. —Preceding unsigned comment added by THE WORLD'S MOST CURIOUS MAN (talk • contribs) 00:40, 21 December 2008 (UTC)

There's some additional studies mentioned at the end of the Miller-Urey article. Also, check out the references in Abiogenesis article. -- JSBillings 01:03, 21 December 2008 (UTC)

Yes - there have been many recreations of the original experiment - and others with conditions closer to those that we now believe to have been present in the early earth. However, these aren't really serious attempts to create life - only to show that the basic building blocks (Amino acids, carbohydrates, etc) could have formed spontaneously in the early planet. Life itself is likely to have been an extreme statistical flook. When the oceans were full of amino acids and other nutrients, it would only take ONE molecule of a self-replicating DNA/RNA type of substance to appear in order for life to get started and for evolution to rapidly do it's thing. Since the process of creating that one molecule could easily have happened just once - in a half billion years and in trillions of cubic meters of water - the probability of being able to reproduce that in a laboratory using the original conditions during the lifetime of the researcher is essentially zero. So the experiment would certainly appear to fail - in that it would not produce life - but that would only prove how statistically infrequent such events must be. SteveBaker (talk) 01:19, 21 December 2008 (UTC)

For quite different kinds of life creating experiments, see Mycoplasma laboratorium. Icek (talk) 08:17, 21 December 2008 (UTC)

Yes - indeed. It seems very likely that we'll be able to produce a completely synthetic life form in perhaps the next decade - but that's a very different thing from reproducing the means by which the first living thing came about on Earth. SteveBaker (talk) 21:03, 21 December 2008 (UTC)

I thought they had given up on the "live from the big ocean" concept and gone to hydrothermal vents and hot springs because the "chemical soup" there would be more reactive? 76.97.245.5 (talk) 12:51, 21 December 2008 (UTC)

Probably - but in terms of answering this question it's still the same deal. We look at ALL of life on earth and every single living thing is clearly descended from a common ancestor because so much of the DNA is shared. This suggests that the 'abiogenesis' event (the first self-replicating molecule coming out of non-living material) may well have been a one-off event - something so amazingly statistically unlikely that it took billions of years and vast number of "attempts" for it to happen. Even if it had to happen at a hydrothermal vent - there are huge numbers of those - and we still have a billion years or so for just one such event to happen....so it's still spectacularly unlikely that we'd be able to reproduce it experimentally. SteveBaker (talk) 21:03, 21 December 2008 (UTC)

Lipid Layer

Which part of the eye produces the lipid layer?96.53.149.117 (talk) 01:51, 21 December 2008 (UTC)

Aren't you the expert on this by now? [1] [2] ? Perhaps you should consult a physiology textbook if you're having a hard time finding the information you need for these articles on the internet at large - I recommend Tortora and Grabowski as an introductory anatomy and physiology textbook. Nimur (talk) 02:04, 21 December 2008 (UTC)

For readers not aware of prior discussion, the answer is quite prominently displayed in a table near the beginning of our Tears article. If the OP is asking something less blindingly obvious and repetitive of his/her recent questions, please clarify. --Scray (talk) 03:09, 21 December 2008 (UTC)

Oh fuck, you are right! I knew I shouldn't have asked this question. Lol, I knew I'd find it there, my bad!96.53.149.117 (talk) 04:46, 21 December 2008 (UTC)

You did know that you would find this fact in that article, because you put it there, as I pointed out earlier. Nimur (talk) 23:14, 21 December 2008 (UTC)

If you had entered your exact question "Which part of the eye produces the lipid layer?" google would have answered your question fully with its first reply. Not a wiki answer but if you put in this query instead "Which part of the eye produces the lipid layer wiki" the first reply is to the wikipedia entry on tears. Please learn to do these very basic types of search first before wasting peoples time, see the bit at the top of this page about trying to answer your question yourself first. Dmcq (talk) 11:35, 21 December 2008 (UTC)

Identifying an unknown mammal

Can someone please help identify this mammal, found in the forests of Peru?

[3], [4] and [5].

I think it is a shrew opossum (Caenolestes caniventer or Lestoros inca), but then I might not be right. Let's see if we can find out! --Leptictidium (mt) 10:08, 21 December 2008 (UTC)

Guessing more like a Thylamys "mouse opossum"? (shorter snout, bigger eyes, monochrome tail) Julia Rossi (talk) 10:54, 21 December 2008 (UTC)

This [6] site has pictures plus a map of S-American mouse opossumice. --Cookatoo.ergo.ZooM (talk) 11:37, 21 December 2008 (UTC)

Skua vs. Great Black-backed Gull - who would win?

No, this isn't going to be another one of *those* threads - rather it's a question based on something I just read in WPs Skua article, namely this:

“ larger species also regularly kill and eat adult birds, up to the size of Great Black-backed Gulls ”

This is absolute bollocks, right? I could envision a Skua taking GBB chicks or eggs, or battling with an adult over food - but really, a fully-grown GBB is *bigger* than the largest Skua and every bit as mean-tempered and predatory. As far as I am aware, nothing short of one of the great eagles would even attempt to make a meal out of a healthy adult bird. --Kurt Shaped Box (talk) 10:58, 21 December 2008 (UTC)

Do you know whether either or both of those species might hunt in groups? OR We have a flock (?) of about 6 crows flying around that harass everything in the neighborhood, including a bird of prey. (Sorry haven't had time yet to look him up.) I've also seen a crowd of swallows take on a magpie. Size isn't everything. 76.97.245.5 (talk) 11:48, 21 December 2008 (UTC)

Not as far as I know. Gulls and Skuas will defend the nesting areas from potential threats en masse but when it comes to hunting and scavenging, it's strictly a competitive activity, with much (often counter-productive) squabbling and bickering. Sometimes I get the impression that preventing a rival from feeding is almost as important to them as getting a meal for themselves (two birds fight, third bird comes in and steals food). --Kurt Shaped Box (talk) 13:11, 21 December 2008 (UTC)

Whats so special about Half-Integer spin? 59.93.92.192 (talk) 13:23, 21 December 2008 (UTC)

Why is it that only particles with half-integer spin, ie fermions, obey the pauli exclusion principle which disallows more than one of the same particle to exist in the same quantum state? —Preceding unsigned comment added by 59.93.92.192 (talk) 13:21, 21 December 2008 (UTC)

The Pauli exclusion principle applies to states with anti-symmetric wavefunctions (Fermions). The Spin-statistics theorem shows that Fermions have half-integer spins. 86.134.187.65 (talk) 16:06, 21 December 2008 (UTC)

Mystery flower

If there's any botanists here, can anybody identify this flower? Unfortunately, I neglected to look at the stem or take a photograph further out, so this is about all I have to identify it with (other than it's in North Carolina, USA). Tastyduck (talk) 15:18, 21 December 2008 (UTC)

Did you find it in a garden or out in the wild somewhere? Since it's dried up for the winter things like color of the flowers etc. can no longer be used to identify it. That makes it a bit tricky. 76.97.245.5 (talk) 23:59, 21 December 2008 (UTC)

This site [7] might help. 76.97.245.5 (talk) 03:06, 22 December 2008 (UTC)

Overcooked vs. burnt food

Chemically speaking, what's the difference between food that is overcooked and food that is burnt? Can food be burnt and *not* be overcooked? --70.167.58.6 (talk) 16:40, 21 December 2008 (UTC)

Well, sort of. You could char a steak on the outside, yet the steak inside is perfectly done. I'd say that "overdone" typically means that something has been cooked so that the chemical properties break down. Cakes become dry, eggs become rubbery, steak becomes a brick. On the other hand, 'burnt' means that you have actually started combusting thing. --Mdwyer (talk) 17:21, 21 December 2008 (UTC)

(ec) 'Burnt' usually implies that there are products of combustion (or pyrolysis, if in a low-oxygen environment) present. The food has been heated past the point of dehydration, allowing elevated temperatures and charring. Note that 'burnt' can be somewhat subjective. The process of caramelization tends to happen just before you get to burning, lending additional flavours. The savoury 'crunchy bits' of grilled and fried foods may be technically 'burnt', but still important to the overall taste of the dish. (Think grilled chicken, calamari, or steak — they wouldn't taste the same without streaks seared into them from the grill surface.)

Overcooked food, meanwhile, need not be burnt. Think of soggy vegetables that have been steamed or simmered into mush, losing all flavour, texture, and nutrients.

'Burnt but not overcooked' is a bit of a semantic issue. While a particular part of a dish might have trouble meeting both criteria, the entire dish overall can have no difficultly being both 'burnt' and 'undercooked' simultaneously. Think of a cake baked at too high a temperature for too short a time — the outside will be blackened, but the inside can still be raw. (Of course, you can do this deliberately; see Baked Alaska.) TenOfAllTrades(talk) 17:24, 21 December 2008 (UTC)

Just for the record, the outside of a Baked Alaska is supposed to be a "delicate brown", not blackened. At least in this neck of the woods. CBHA (talk) 17:39, 21 December 2008 (UTC)

Yeah, I should have been a bit more specific. I was referring to the general principle of the insulating properties of cake, rather than the specific details of the recipe. :D TenOfAllTrades(talk) 17:52, 21 December 2008 (UTC)

I figured that was probably the case. I just did not want anyone burning their Alaska based on what they read in Wikipedia. After all, one can see Russia from there. Or so I hear. Wanderer57 (talk) 18:42, 21 December 2008 (UTC)

One might want to read about the Maillard reactions, a class of chemical reactions which include both "browning" and "carmelization" and a number of other chemical reactions that make cooked food "tasty". --Jayron32.talk.contribs 02:03, 22 December 2008 (UTC)

Crème brûlée? --Maltelauridsbrigge (talk) 11:02, 22 December 2008 (UTC)

In Fact, you can have food that is burnt, but undercooked. If you put food in the oven at too high a temperature, for example, the exterior may become burnt before the interior has been fully cooked. 142.177.59.188 (talk) 12:35, 31 December 2008 (UTC)

Wood-burning stoves, creosote and soup cans

The local farmer who blows out our driveway and shovels the deck around the house likes to give advice to us former "city slickers". Sometimes, I think he is pulling our collective legs; however, as today's tip was about fire safety, I thougt I'd check it out here. (I have googled various combinations of the title of the section to no avail.) Creosote build-up in a chimney is the biggest danger for house fires. We do all the sensible things: burn only well-seasoned hardwood, clean the chimney at least twice a season, and burn the wood at a sufficiently high temperature to discourage the creosote from sticking to the chimney liner. The farmer says that another trick is to throw in a couple of empty soup cans and burn them daily. He claims there is a chemical given off in the burning that also inhibits the formation of creosote on the liner. He didn't know what chemical it was, or if it was in canned goods other than soup, or if it could be purchased in some other form. I doubt we open two tins in a month, but are willing to make some sacrifices (or borrow tins from the neighbours' recycling bins) if it will help prevent a house fire. Any thoughts, pro or con? Thanks for any help you can provide. ៛ Bielle (talk) 18:03, 21 December 2008 (UTC)

I doubt he's pulling your leg intentionally, but he might be a victim of some old wives' tale. There do exist chemicals that can be burned to clean out your chimney. In theory, they catalyze the creasote into a form that falls down the chimney instead of sticking. However, there seems to be quite a lot of doubt as to if they actually work or not. [8] In any case, a chimney fire can be devastating, so have your chimney inspected at least every couple of years. --Mdwyer (talk) 18:16, 21 December 2008 (UTC)

If you only look down your chimney every couple of years, on the off years you won't be able to enjoy your fire because you'll be sitting there wondering how much creosote is in there. Make a chimney inspection part of your winterization routine, and run a brush down it anyway. There's another old husband's tale about flashlight batteries, but I never tried it, for two reasons: I didn't want whatever was released by burning a battery to be near me (zinc, at least, I guess), and I didn't want stuff in my ashes because I used them for traction on ice in my truck. --Milkbreath (talk) 12:47, 22 December 2008 (UTC)

Have a look at our Bisphenol A page. If your cans are coated inside with synthetic resin, which I assume is precisely what is supposed to create the presumed effect, you would end up with this and similar/worse chemicals in the air around your fire. Ideally it would all go up the chimney and "harmlessly" pollute the air outside, but do you really wish to bet your health on that. If the stuff is caustic enough to scrub creosote off the large surface area of you chimney, I don't want to know what it will do to mucous membranes and lung tissue of your respiratory tract.76.97.245.5 (talk) 07:37, 22 December 2008 (UTC)

Yeah, at best it sounds like an old-wives-tale, at worst actively harmful. I'd say what you're doing now (regular inspection/cleaning of the chimney, not burning dodgy wood) is all you need to be doing. ~ mazca ^t|c 09:22, 22 December 2008 (UTC)

Most hardware stores and supermarkets have commercial "chimney cleaning logs." Most of these are environmentally friendly. So, buring one or two of these a season along with having your chimney inspected and cleaned (if these logs work like they are supposed to, then actual cleaning will be a minimum) would likely be the best bet. Better safe than sorry!

Esclorophile Bush?

The "word" esclorophile appears in the article Tlalpan. Not knowing what it is, I searched for it using Google and found it in only three places on the internet. I'm wondering based on this if it is a real word or an error or vandalism.

Can anyone help with this? Thanks. Wanderer57 (talk) 18:28, 21 December 2008 (UTC)

The three Google hits were all from the Wikipedia page. If you look at the next paragraph in the Wikipedia article, the word appears spelled "esclerophile". This word is not in any online dictionary I could find, including the Oxford English Dictionary, but the "-scler-" part gives us a toehold. In words like "sclera" and "sclerosis" it means "hard" after the Greek. It's my guess that it's really "esclerophile" and means "hard-loving" in reference to the rocky terrain. "Esclerophile" yields a few non-Wikipedia hits on Google. --Milkbreath (talk) 18:54, 21 December 2008 (UTC)

I've just cleaned up that article, and I chose to retranslate that word as "sclerophyllous". How did I know? Because the Spanish WP article es:Esclerófilo is cross-linked to the English WP's Sclerophyll. --Heron (talk) 19:54, 21 December 2008 (UTC)

I have redirected Esclerophile to Sclerophyll in case it pops up in the future. Nimur (talk) 23:34, 21 December 2008 (UTC)

Paranoid park (spoiler warning)

In Paranoid park a guard gets cut into two, if I remember correctly somewhere below the waist, and after this for some seconds his upper part crawls away (supported by the arms) from the lower part. Is this really possible??? Lova Falk (talk) 19:58, 21 December 2008 (UTC)

I would expect the blood loss, organ damage, and likely spinal damage to make such a thing very unlikely... --98.217.8.46 (talk) 20:48, 21 December 2008 (UTC)

It would depend upon where the guard got cut into two pieces. If it was the lower spinal region, it would avoid any paralysis in the upper body so the arms could still be used. This would also avoid damage to organs except, perhaps, the intestines. The blood loss is an issue but if the person was particularly strong willed to pain it might be possible for a few seconds. —Cyclonenim (talk · contribs · email) 21:20, 21 December 2008 (UTC)

Isn’t the guy cut in half by a freight train? It’s not a super clean cut like from a nihontō or something. A train is likely to cause much more physical trauma. I think that degree of movement would be unlikely. --S.dedalus (talk) 21:59, 21 December 2008 (UTC)

I wouldn't know, I've never seen the film. You're right, if it's a train then I doubt very highly it could occur. But if the person were cut in half in a clean cut, it might. —Cyclonenim (talk · contribs · email) 23:21, 21 December 2008 (UTC)

This seems to me just an exaggeration of Mike the Headless Chicken. — Sebastian 05:45, 22 December 2008 (UTC)

Ah, what a sissy! Klaus Störtebeker walked along twelve of his companions after he was beheaded! 95.112.137.182 (talk) 18:14, 22 December 2008 (UTC)

As also St. Denis, who walked about two miles after being beheaded, carrying his head and delivering a sermon. - Nunh-huh 20:52, 22 December 2008 (UTC)

Though some say St.Denis was a ventriloquist [9], and only moved his lips pretending he was speaking --PMajer (talk) 10:24, 23 December 2008 (UTC) 21:08, 22 December 2008 (UTC)

If the injury is sharp (a cut rather than a crush) then what you describe wouldn't happen. Such an injury would sever the inferior vena cava and the descending aorta. Blood would squirt from the openings of both vessels, the arterial blood with some force. This would leave the blood pressure in both vessels very low, and in turn the blood from the superior vena cava and the carotid arteries would drain under pressure into their lower counterparts. The cerebral blood pressure would immediately collapse, causing the prompt cessation of cognitive and motor functions. The uncinematic reality of most mortal injuries is that people just crumple up like a puppet with its strings cut, rather than staggering around delivering lapidary epitaphs before lying down. 87.114.130.249 (talk) 21:36, 22 December 2008 (UTC)

Going back to the OP we should recall that the scene of the guard's death was an oneiric sequence or in any case, a scene in the imagination of the boy, who got shocked hearing about an accident in the news; so the episode is expressly unreal (is it so, or is it mine a dream of a dream?) --PMajer (talk) 10:47, 23 December 2008 (UTC)

Possibly - but it's irrelevent - we know that the scene is in a work of fiction, that it's a fiction inside a fiction doesn't help! The question is about reality...and it's pretty clear that the fiction (or meta-fiction...or fiction²) is incorrect. Certainly, blood pressure would drop to zero pretty much instantly (the veins and arteries are not going to pose much of a resistance to the blood flowing out) - which means that the motive power to the brain gets switched off like a light switch and loss of consciousness is almost instantaneous. Cases of bodies twitching and eyes rolling and other 'spooky' things happening shortly after death are due to now uncontrolled muscles using up the last of their energy...but the idea that there is still intent and consciousness driving them is not reasonable. Mike the chicken is weird...but he wasn't COMPLETELY headless - he still had one ear and enough brain-stem for the kinds of things chickens need to do to behave. That he survived the trauma and blood loss is the amazing thing. SteveBaker (talk) 14:36, 23 December 2008 (UTC)

Well, I assumed the question was mainly about the movie rather than about the human anatomy. The scene appears indeed unreal even without a PhD in medicine, so one can ask, what is the meaning of it. Anyway, I feel better since you confirm that it is scientifically impossible :) --PMajer (talk) 20:16, 23 December 2008 (UTC)

No, the question was about human anatomy. I did not interpret the scene as something happening in the imagination of the boy. Lova Falk (talk) 20:30, 23 December 2008 (UTC)

It is true that blood pressure would collapse immediately, but that is not to say that someone cannot remain conscious even momentarily for a few seconds! We know that cells can survive by anaerobic respiration, which is why the brain can survive for a few minutes without O₂ so with significant pain tollerance it could be possible to remain conscious for a few more seconds. This is why you can survive a heart attack temporarily before CPR is initiated, since cells can survive adequetely for a while on no oxygen. —Cyclonenim (talk · contribs · email) 19:41, 23 December 2008 (UTC)

No blood FLOW is not the same thing as no blood PRESSURE. When your heart stops, the blood still in the vessels inside your brain still contains oxygen that can presumably be extracted to keep you alive for quite a while...after all, blood flows around in a big loop giving up a little oxygen to each part of the body as it goes around. So if it merely stops flowing for a while, you'd presumably still be extracting some oxygen from it for quite a while. But when the pressure drops to zero and it flows out - that's simply not possible - so I'd expect you to black out so much sooner. SteveBaker (talk) 21:23, 23 December 2008 (UTC)

Metal detectors for non-magnetic metals

If I remember right, metal detectors (I'm talking about the security ones, not the ones people use to go and find things underground) can detect non-magnetic metals. For example, if you've had a titanium rod or plate put into your body in an operation, you have to tell the metal detector operator because you'll set it off simply with the metal in your body. The metal detector article seems to say that metal detectors depend on electromagnetic processes (forgive my lack of electromagnetic knowledge) to find metal, but I couldn't find anything in the article regarding non-magnetic metals. How is it that these detectors pick out titanium, aluminium, etc.? Nyttend (talk) 22:15, 21 December 2008 (UTC)

Titanium and aluminium / aluminum are paramagnetic. An external magnetic field will, therefore, still detect the metal as it becomes weakly magnetic, albeit temporarily. --Cookatoo.ergo.ZooM (talk) 22:49, 21 December 2008 (UTC)

How is it, then, that people with titanium in their bodies can, in certain circumstances, undergo MRIs safely? Is it just really weakly magnetic, too little to be pulled out of place by the MRI magnets? I'm not challenging you, just confused. Nyttend (talk) 22:58, 21 December 2008 (UTC)

Titanium is not magnetic enough to be pulled around in an MRI. Also, it produces very little "artifact" (a term used by MRI operators for the weird glows caused by metals in general). Therefore, titanium tools for use around MRI machines is becoming popular, as well as titanium screws, staples, and such. Now, you should note that there is not claim that titanium is not pulled around at all or that it produces no artifact at all. It just isn't enough to be of any concern. -- kainaw™ 00:03, 22 December 2008 (UTC)

Thanks for the helpful explanations — I think I understand this a lot better than when I posted the question in the first place. Nyttend (talk) 00:37, 22 December 2008 (UTC)

As the article says, many (most) metal detectors create an oscillating magnetic field. Therefore the magnetic field strength is changing all the time and a changing magnetic field causes induction of electric currents in a conductor - in this case eddy currents, which in turn create their own magnetic field which is opposed to the original magnetic field (see Lenz's law). Thus, the total magnetic field strength (which is measured by the device) will be smaller in the presence of a conductor. While human tissue is a conductor too, most metals are better conductors, and cell membranes surpress eddy currents (as a side note, when constructing a transformer, you want to minimize eddy currents, and this is usually done by using thin plates electrically insulated from each other as magnetic conductors; vibration of these plates causes the humming sound of transformers). Icek (talk) 09:13, 22 December 2008 (UTC)

And since you brought up the issue of metals and MRI, you might also be interested in the MRImetalDetector.com blog which has information on ferromagnetic (only) metal detection systems for use in MRI patient pre-screening. Tgilk (talk) 14:05, 12 September 2009 (UTC)