Wikipedia:Reference desk/Archives/Science/2013 August 6

= August 6 =

Which human ancestors invented fire?
In the course of evolutionary history ,Which human ancestors invented fire?

AmRit GhiMire &#39;Ranjit&#39; (talk) 00:26, 6 August 2013 (UTC)


 * Probably Homo erectus: see Control of fire by early humans. AndyTheGrump (talk) 00:30, 6 August 2013 (UTC)


 * And that would be "discovered how to use fire", not "invented". StuRat (talk) 00:39, 6 August 2013 (UTC)
 * Roasting, stewing, frying, and baking of food with fire could be considered "inventions," since at the time they were new and useful processes, resulting from happy accidents, or from observation and experimentation. Edison (talk) 14:47, 6 August 2013 (UTC)


 * There is also a distinction between those who used fire that they found in their environment (from forest fires, lightning, volcanoes, whatever) and those who created the means to make it from scratch. The latter would definitely be an "invention"...and I think that this is what we should probably be discussing here. SteveBaker (talk) 16:25, 6 August 2013 (UTC)

Type of solid
What is the term for a covalent network solid that melts by ionising? For example, -ABABA- → AB+ + ABA-. Plasmic Physics (talk) 04:48, 6 August 2013 (UTC)
 * Generally, covalent network solids (like diamond, silicon, Bakelite, etc.) melt WITHOUT ionizing. Can you give an example of a covalent solid that ionizes as it melts? 24.23.196.85 (talk) 04:56, 6 August 2013 (UTC)
 * I'm certain that some of the hyperfluorinated metals exhibits this sort of behavior, though I can't seem to find a good example at the moment. Plasmic Physics (talk) 05:03, 6 August 2013 (UTC)
 * Metal fluorides are ionic solids, not covalent. 24.23.196.85 (talk) 05:42, 6 August 2013 (UTC)


 * Not generally, that is an over-simplification taught in secondary schools, just like "the conjugate of a weak base, is a strong acid" which is not strictly true either. See aluminium fluoride for an example of a covalent metal fluoride. Plasmic Physics (talk) 05:51, 6 August 2013 (UTC)
 * Correct, but AlF3 breaks up into neutral molecules upon melting, not into ions. 24.23.196.85 (talk) 07:44, 6 August 2013 (UTC)


 * Indeed. However, I did not give it as an example of the substance in question, but only of a non-ionic metal fluoride. Plasmic Physics (talk) 08:36, 6 August 2013 (UTC)


 * Do any of the transition metal hexafluorides qualify? And ReF7? Double sharp (talk) 07:45, 7 August 2013 (UTC)


 * None of the ones list on WP, or rhenium heptafluoride are covalent networks. Plasmic Physics (talk) 08:04, 7 August 2013 (UTC)
 * Struck out my question above Brain was not retrieving information properly – oops! Double sharp (talk) 08:43, 7 August 2013 (UTC)


 * Some sort of homoassociation of the parts? DMacks (talk) 05:56, 6 August 2013 (UTC)


 * Perhaps. Would it be a two step process, whereby the solid breaks into individual monomeric molecules, followed by their homoassociation? Plasmic Physics (talk) 07:05, 6 August 2013 (UTC)


 * It will be the other way around -- the solid will first break into neutral molecules, which may then self-ionize (but only to a small extent). 24.23.196.85 (talk) 01:41, 7 August 2013 (UTC)


 * No offense, but I'm certain that that is the same order as what I used. Plasmic Physics (talk) 02:18, 7 August 2013 (UTC)

Is solid oxonium hydroxide stable under pressure, or does it require an applied electric field? I wonder how the density would be different from ice. Plasmic Physics (talk) 07:14, 6 August 2013 (UTC)
 * Do you mean hydronium hydroxide (also known as dihydrogen monoxide)? If so, it is stable under pressure, but experiences melting point depression and requires supercooling to remain in solid form (it will melt under pressure otherwise).  As for the density, it's the same as that of ice -- for obvious reasons! 24.23.196.85 (talk) 01:32, 7 August 2013 (UTC)


 * No, I'm not using a pseudonym (yes, pseudo-, not syno-) for molecular water. I'm talking about a legitimate salt of composed of discrete ions. Plasmic Physics (talk) 02:18, 7 August 2013 (UTC)
 * I ask because I know that an equilibrium shift can occur as a consequence of a change in pressure, I also know that this is only applicable to gases, as solids and liquids are incompressible. However, I also know that that last bit is only true for relatively small changes in pressure. Solids and liquids can actually compress under MPa pressures and higher. So, I wondered if MPa or greater pressures, could indeed shift the Kw away from water. Plasmic Physics (talk) 02:27, 7 August 2013 (UTC)
 * If you're looking for a solid composed entirely of H3O+ and OH- ions, you won't find it anywhere -- such a solid cannot exist because of energy considerations. Only in a plasma can water be completely ionized! 24.23.196.85 (talk) 04:11, 7 August 2013 (UTC)


 * I care to know what these energy considerations are - Gibbs, entropy, enthalpy, etc. (FYI I thought that the water decomposes into the elements before becoming a gas plasma.) Plasmic Physics (talk) 04:18, 7 August 2013 (UTC)


 * In lay terms, it takes so much energy to ionize the water molecules and separate the resulting ion pairs that the water (ice) will vaporize first regardless of applied pressure. I thought you, of all people, would know this? 24.23.196.85 (talk) 02:20, 10 August 2013 (UTC)

American plague
European diseases killed many native americans, why did not american diseases kill the europeans? — Preceding unsigned comment added by 128.214.48.186 (talk) 09:59, 6 August 2013 (UTC)


 * The Straight Dope tacked this thoroughly. 184.147.136.32 (talk) 11:28, 6 August 2013 (UTC)


 * This was discussed a couple of weeks ago - see Reference desk/Archives/Science/2013 July 13. Clarityfiend (talk) 13:16, 6 August 2013 (UTC)


 * European diseases may not be the whole story. Count Iblis (talk) 13:49, 6 August 2013 (UTC)


 * In the Jamestown colony, most of the settlers died their first year. Lack of food was a cause, but they also died from malaria, dysentery and "fevers." The local germs may have been strains they had not encountered back in Britain. The river water may have been nasty, but so were many rivers in England. The local natives  were likely not only living in healthier locations, but probably had more natural resistance to the local pathogens.  Edison (talk) 14:39, 6 August 2013 (UTC)


 * Jared Diamond wrote perhaps the definitive work on this exact subject (at least as far as material that is accessible to a wide audience), if you're looking to understand the subject in detail. I recommend the book in any event as a must-read, but here's the long and the short of it - animal domestication.  Most infectious diseases pass into the human population for the first time as a result of zoonosis and as Eurasians had been living in close proximity with their domesticated species for many thousands of years by the point of time in question, they had built a healthy collection of diseases, but also had steadily built immunities to the same, limiting their virulence.   Native Americans, by comparison, had only a handful of domesticated species (only a very small portion of all species on the planet possess a social nature and other features which make them good candidates for steady and lasting domestication through the methods that are available to a non-technologically advanced people), which were not very well dispersed geographically and as such had not developed nearly as extensive a collection of diseases/immunities.  Unfortunately for these peoples, they also lacked the immunities necessary to protect them against the diseases brought with Europeans, and even the pathogens that had relatively mild effects on their Eurasian hosts of this era could in some cases prove deadly to their new American hosts, to say nothing of a disease like small pox, which spread well in advance of the Europeans themselves.  Snow (talk) 00:27, 7 August 2013 (UTC)


 * Another factor was that indigenous Americans, having had little experience with deadly epidemics, did not have cultural coping techniques like quarantine. They learned, to be sure, and survival rates went up when practices like quarantine were enforced. But at first the natural reaction was exactly the kind of thing that exacerbates epidemics. This is beside the point of why did not "american diseases kill the europeans?" Folks like Jared Diamond have tackled that quite well. Pfly (talk) 10:37, 8 August 2013 (UTC)

DNA questions
--Czech is Cyrillized (talk) 23:46, 6 August 2013 (UTC)
 * 1) How many codons are there in a base pair?
 * 2) What is the size in megabytes of the human genome?
 * One codon equals three base pairs, so there is 1/3 of a codon per base pair. Estimates of the number of base pairs in the human genome vary a bit due to technical reasons, but the most recent value I've seen is around 6.3 billion (in women, with two X chromosomes rather than an X and a Y).  Since each base pair contains two bits of information, that yields slightly under 1.6 GB of information. Looie496 (talk) 00:11, 7 August 2013 (UTC)
 * You can download each chromosome (or those for any of 50 or 60 other species) here. If you grab the "GBK" file, you can unzip it and watch a sea of A's, G's, C's and T's scroll by.  I was able to download the full set within a minute or so...and with compression - the whole thing fits comfortably onto a double-sided CD-ROM.  You don't even need a DVD, let alone a BluRay disk.  It's kinda humbling actually.  :-) SteveBaker (talk) 02:36, 7 August 2013 (UTC)
 * Because of this compactness I've always thought of the human genome as a good demonstration of the power of procedural generation (yes, I realise that the analogy isn't exact). Equisetum (talk &#124; contributions) 19:12, 8 August 2013 (UTC)