Wikipedia:Reference desk/Archives/Science/2021 March 31

= March 31 =

What prevents Earth from sinking to its core?
Earth core temperature is superhot to melt almost anything, then what prevents Earth from sinking to its core? Rizosome (talk) 11:04, 31 March 2021 (UTC)
 * What makes you think it isn't? ←Baseball Bugs What's up, Doc? carrots→ 11:19, 31 March 2021 (UTC)
 * Um, what is it going to "sink" into? When it sinks into it, what will the material that was there do?  The earth's 4 billion year lifespan has already caused it to reach hydrostatic equilibrium, which means it is (roughly) already organized by density, with the most dense materials at the core, and becoming less dense as you move outward.  Simply put, everything which could sink to the core already has.  Things like convection currents in the Earth's mantle drive dynamic processes like plate tectonics, by which portions of the crust are recycled into the mantle (at subduction zones) and portions of the mantle bubble up to form new crust (at mid-ocean ridges).  However, these effects are basically only happening in the lithosphere/asthenosphere (i.e. crust and upper mantle) regions; which amounts to the equivalent of the skin on an apple.  Everything underneath that is well organized by density, and in a fairly stable dynamic equilibrium. -- Jayron 32 11:33, 31 March 2021 (UTC)
 * I suggest you read one of the many WP articles on this. You could start at Structure_of_Earth. Mike Turnbull (talk) 11:37, 31 March 2021 (UTC)

so Earth core temperature is not enough to melt Earth to its core? Rizosome (talk) 11:45, 31 March 2021 (UTC)
 * Part of the earth's core is fluid, see Earth's outer core; convection currents in the outer core are believed to be the source of the Earth's magnetic field. On the other hand, Earth's inner core is solid, despite being hotter, because it is more dense due to the extreme pressures caused by the weight of the material around it; that is to say that the inner core is solid because higher pressure causes most materials to be more likely to be solids than liquids at a given temperature.  -- Jayron 32 12:09, 31 March 2021 (UTC)


 * "The crust lies on top of the mantle, a configuration that is stable because the upper mantle is made of peridotite and so is significantly more dense than the crust". In other words, the crust floats on the mantle. Alansplodge (talk) 13:02, 31 March 2021 (UTC)
 * Yes. That's what I said.  -- Jayron 32 13:34, 31 March 2021 (UTC)


 * Earth's mantle, Earth's outer core, and Earth's inner core do not give densities. I was unable to find densities for all layers in any single article, and the only density for the mantle I found was from our Planetary differentiation, and that appears to be for the very top of the mantle.
 * Densities currently given in Wikipedia:
 * Upper Crust: 2.69 - 2.74 g/cm3 -- Earth's crust
 * Lower Crust: 3.0 - 3.25 g/cm3 -- Earth's crust
 * Mantle (presumably top of upper mantle): 3.4 g/cm3 -- Planetary differentiation
 * Outer Core: 9.9 - 12.2 g/cm3 -- Structure of Earth
 * Inner Core: 12.6 - 13.0 kg/cm3 -- Structure of Earth
 * Mean density of the planet as a whole: 5.515 g/cm3 -- Planetary differentiation
 * Densities from The Interior of the Earth by Eugene C. Robertson, USGS; Derived from information in Don L. Anderson's Theory of the Earth (1989):
 * Crust: 2.2 - 2.9 g/cm3
 * Upper mantle: 3.4 - 4.4 g/cm3
 * Lower mantle: 4.4 - 5.6 g/cm3
 * Outer core: 9.9 - 12.2 g/cm3
 * Inner core: 12.8 - 13.1 g/cm3
 * -- ToE 14:59, 31 March 2021 (UTC)

, I realize I might as well be talking to a brick wall, since you never answer questions that could help us understand your queries, but why do you think the melting of material in the Earth's core would mean the material above it has to sink? Your response to seems to show that you are presenting a false dichotomy; you ask us why things don't sink into the melted core, we explain why, and you respond by asking us if we are saying the core isn't melted because things don't sink into it. This isn't an either/or proposition. Sinking has to do with things like buoyancy and density, which are not necessarily coupled directly or linearly to physical states. An aircraft carrier is mostly made out of metal, and it floats on a liquid ocean. An iceberg is mostly made out of solid material, and it floats on liquid. The conditions in the Earth's core are so extreme in terms of temperature and pressure that one cannot assume that liquid material in those conditions necessitate solid material above it sinking into it. --OuroborosCobra (talk) 16:50, 31 March 2021 (UTC)

Why density comes into factor in my question rather than thermodynamics? Rizosome (talk) 02:52, 1 April 2021 (UTC)
 * , you asked a question about material sinking or not sinking. Sinking is not a thermodynamically driven process. I'm going to ask you to restate your question if you mean it to be a thermodynamic one, including exactly what you think the thermodynamics of this system are and how they relate to your question. --OuroborosCobra (talk) 03:35, 1 April 2021 (UTC)

Earth's orbit shrinking?
In the Sun life phases section, I came across the following statement:
 * According to a 2008 model, Earth's orbit is shrinking due to tidal forces.

I know the Earth is moving away from Sun at about 1.5 cm/year due to solar mass loss rate (and probably other reasons). Could someone correct me or revise the article if needed? Almuhammedi (talk) 14:45, 31 March 2021 (UTC)


 * I've read the cited article and I think I understand a bit that as a special case during solar evolution. Please, correct me if I were wrong.Almuhammedi (talk) 15:08, 31 March 2021 (UTC)


 * The statement in question was added on 18:45, 20 February 2016 by User:rolf h nelson. A new ref was not provided for it in that edit, but it is likely supported by the 2008 reference (name=schroder) given later in that paragraph: Schröder, K.-P.; Connon Smith, R. (2008). "Distant future of the Sun and Earth revisited". Monthly Notices of the Royal Astronomical Society. 386 (1): 155–163. arXiv.  I'll leave it to others to address the substance. -- ToE 15:28, 31 March 2021 (UTC)
 * The orbit shrinkage will take place at the end of the AGB phase, it will be very rapid and will spell the end of this here planet (according to the paper; we would now have to be at at least 1.15 AU in order to survive). This is shown in Fig.2 in the paper, which also shows that Earth will be at 1.03 AU then, its orbit still increasing due to the substantial solar wind in the AGB phase (an acceleration of the current orbit growth that Almuhammedi mentions), until it is engulfed by the Sun's, what is it?, chromosphere at which point it will start to fall in. --Wrongfilter (talk) 17:08, 31 March 2021 (UTC)


 * User:rolf h nelson's 18:45, 20 February 2016 edit did not imply current orbit shrinking, as they wrote:
 * According to a 2008 model, the Earth, its orbit shrinking due to tidal forces (and, eventually, drag from the lower chromosphere), is engulfed by the Sun near the end of the AGB phase.
 * The very next edit, at 20:54, 20 February 2016, was an attempt by User:JorisvS (no long an active editor) to clarify the language, but it inadvertently changed the meaning to state the the orbit shrinking is happening now:
 * According to a 2008 model, Earth's orbit is shrinking due to tidal forces (and, eventually, drag from the lower chromosphere), so that it is engulfed by the Sun near the end of the asymptotic-giant-branch phase.
 * The sentence was further edited later that year (at 12:57, 18 December 2016) by User U-95 (also no longer active), commenting that "Check the referred article. According to it, Earth will not make to the AGB phase.", and bringing the sentence to its current form:
 * According to a 2008 model, Earth's orbit is shrinking due to tidal forces (and, eventually, drag from the lower chromosphere), so that it is engulfed by the Sun near the tip of the red giant branch phase, 3.8 and 1 million years after Mercury and Venus have respectively suffered the same fate.
 * Do you wish to clean up what was done to your old material (while checking to see if U-95's addition is correct -- and perhaps using less confusing wording so JorisvS's misunderstand doesn't reoccur), or should we? It would be good to have a subject matter expert who knows if the results of this 2008 model are still considered novel enough that they be attributed as such, or if they are the current consensus and they can just be stated as a consequence of the Sun's stellar evolution.
 * And thank you Almuhammedi for identifying this error. It always amazes me that fairly obvious errors such as this can persist as long as they do (over five years in this case) in such a prominent article. -- ToE 02:32, 1 April 2021 (UTC)

Thank you all for your active support and quick response too. Almuhammedi (talk) 10:55, 1 April 2021 (UTC)

I've edited the sentence to read:
 * According to a 2008 model, Earth's orbit will have initially expanded significantly due to the Sun's loss of mass as a red giant, but will later start shrinking due to tidal forces (and, eventually, drag from the lower chromosphere) so that it is engulfed by the Sun during the tip of the red-giant branch phase, 3.8 and 1 million years after Mercury and Venus have respectively suffered the same fate.

I've also asked for some subject matter expert attention at Talk:Sun. -- ToE 12:21, 2 April 2021 (UTC)

Pre-Darwinian Scientists that linked humans to apes.
I’m looking for examples of scientists that explored theories about our closeness to primates before Darwin, ideally just before. I think that Lamarck had theories that suggested a direct evolution from primates to humans (as opposed to Darwin’s idea that we share a common ancestor) but I can’t seem to find any specific details.95.150.37.235 (talk) 21:00, 31 March 2021 (UTC)


 * The connection was first described in print by Thomas Henry Huxley in his 1863 book, Evidence as to Man's Place in Nature. Darwin had previously avoided mentioning the subject, probably on the grounds that his theories on animal evolution were already controversial enough. Alansplodge (talk) 23:45, 31 March 2021 (UTC)
 * See Historical background of primate studies for some earlier observations about the relationship, going back to Galen and Albertus Magnus; although the notion that there was any common ancestor seems have occurred first to Darwin and his chums. Alansplodge (talk) 00:04, 1 April 2021 (UTC)
 * Our article on James Burnett, Lord Monboddo says,
 * "Monboddo debated with Buffon regarding man's relationship to other primates. Charles Darwin did not mention Monboddo, but commented on Buffon: "the first author who in modern times has treated [evolution] in a scientific spirit was Buffon". Buffon thought that man was a species unrelated to lower primates, but Monboddo rejected Buffon's analysis and argued that the anthropoidal ape must be related to the species of man: he sometimes referred to the anthropoidal ape as the "brother of man"."


 * —Deor (talk) 17:10, 1 April 2021 (UTC)
 * In his 1774 book Of the Origin and Progress of Language Monboddo poses the question, what would be the criterion and distinguishing mark of difference, betwixt men and the Orang Outang, in his present state? After a lengthy discussion he concludes, contra Buffon, that we ought to decide, that the Orang Outangs are men. (His "Orang Outang" is a general name for the great apes of Africa.) I have not found where he uses the characterization "brother of man". --Lambiam 15:27, 3 April 2021 (UTC)


 * Some further reading here and especially here for context. Matt Deres (talk) 13:27, 3 April 2021 (UTC)