Q. People used to think the moon was knocked out of hole in the earth, leaving behind the Pacific Ocean. At any rate, it would just fit. If you put it down there really, really gently, would we be ok living on an earth with a moon balanced on it?
A. No. The surface of the crust is nowhere near enough to support a protrusion on the surface a large fraction of the size of the planet. It would settle. Having a density similar to that of magma, it would not plunge straight to the centre of the earth, possibly ejecting large fractions of the earth into an escape velocity in a gigantic "splash", but would certainly become immersed, engendering a massive rise in magma levels.
You probably know the massive destruction a large Tsunami can wreak on coastal (and not so coastal) cities, forests, stuff, etc. A largest tsunami is less than a mile high, and might kill hundreds of thousands of people and scour hundreds of square miles of land.
Now imagine a a tidal wave several thousand miles high which is made of hot lava. This is not a human survival positive indicated event. I'm not sure even the cockroaches are going to like this one. I mean, I'm sure some of the bacteria may survive, but I don't know if they'll survive on Earth, or only by having previously escaped the Earth and drifting in interstellar space, hoping to waft into another hospitable planet. There are some bacteria that might survive being frozen to near absolute zero[1], but not, I think, vaporisation.[2]
Ah, you say, but what about humans, or bacteria, buried safely at the bottom of a disused mine-shaft, under a mountain? Well, there are two problems with this: (1) a few isolated bacteria and no other biota in existence may, upon resumption of a decent environment, be able to recolonise from scratch. Humans, not so much. (2) the in-a-mineshaft plan depends heavily on the mineshaft being buried safely just below the surface of the earth's crust, and as I think I indicated previously, I strongly suspect the entirety of the earth's crust to be the front-line casualty in a moon-magma-plop scenario.
As a comparison (in the tradition of the awesome demonstration in The Core), consider an orange filled with boiling-hot jello[3]. Put some ants on the surface. Now smash the orange with a hammer (to simulate the splash) and whack all the bits of peel a few more times (to simulate the effect of very high G on human anatomy). Then scoop it all back together again, mixing the bits of peel with the surface of boiling jello. Examine the ants. Did any survive?
Of course, this is unfair. Suppose the moon is immersed carefully in the magma. This would merely cause the earth's surface to expand a bit, leading to massive tectonic upheaval, but life perched carefully in the middle of relatively stable continental plates may be ok. Or suppose it's levitated carefully to just touch the bottom of the ocean but not fall any further. Assuming the moon is stable under its own gravity to hold together enough that no bits fall off in the Earth's gravity (which would result in a mess similar to scenario #1) This will merely cause a lot of nearby water and possibly mountains to fall sideways off the earth and onto the moon, causing more traditional world-wise Tsunamis that may be made of water rather than lava. In both cases, primitive biota and mammals cosying in mine shafts may be ok.
[1] And viruses, but bacteria need water and some useful chemicals to come back to life. Viruses need bacteria.
[2] I use the term "Tidal wave" despite the "tidal" being considered a misnomer. Despite the name, these waves are typically not being caused by the moon, which causes many pedants to prefer the more euphonious "Tsunami". However, as I have been at quite unnecessary pains to explain, the wave I'm discussing here IS caused by the moon. So I'm going to say the not-quite-correct "Tidal wave" in the hopes that bad pedants will be annoyed and good pedants will think it's funny.
[3] I have no justification for choosing the American proprietary term "Jello" rather than the British generic term "Jelly", but did so PURELY to annoy pedants. However, it occurred to me because it (1) sounds funnier and (2) suggests clearly that I'm referring to desert jelly, rather than royal jelly, petroleum jelly, gelignite, American-made jam, or any other anatomic, biological, lubricating or industrial substance which wobbles or has a similar technical name and picked up the descriptor "Jelly" somewhere along the line.
A. No. The surface of the crust is nowhere near enough to support a protrusion on the surface a large fraction of the size of the planet. It would settle. Having a density similar to that of magma, it would not plunge straight to the centre of the earth, possibly ejecting large fractions of the earth into an escape velocity in a gigantic "splash", but would certainly become immersed, engendering a massive rise in magma levels.
You probably know the massive destruction a large Tsunami can wreak on coastal (and not so coastal) cities, forests, stuff, etc. A largest tsunami is less than a mile high, and might kill hundreds of thousands of people and scour hundreds of square miles of land.
Now imagine a a tidal wave several thousand miles high which is made of hot lava. This is not a human survival positive indicated event. I'm not sure even the cockroaches are going to like this one. I mean, I'm sure some of the bacteria may survive, but I don't know if they'll survive on Earth, or only by having previously escaped the Earth and drifting in interstellar space, hoping to waft into another hospitable planet. There are some bacteria that might survive being frozen to near absolute zero[1], but not, I think, vaporisation.[2]
Ah, you say, but what about humans, or bacteria, buried safely at the bottom of a disused mine-shaft, under a mountain? Well, there are two problems with this: (1) a few isolated bacteria and no other biota in existence may, upon resumption of a decent environment, be able to recolonise from scratch. Humans, not so much. (2) the in-a-mineshaft plan depends heavily on the mineshaft being buried safely just below the surface of the earth's crust, and as I think I indicated previously, I strongly suspect the entirety of the earth's crust to be the front-line casualty in a moon-magma-plop scenario.
As a comparison (in the tradition of the awesome demonstration in The Core), consider an orange filled with boiling-hot jello[3]. Put some ants on the surface. Now smash the orange with a hammer (to simulate the splash) and whack all the bits of peel a few more times (to simulate the effect of very high G on human anatomy). Then scoop it all back together again, mixing the bits of peel with the surface of boiling jello. Examine the ants. Did any survive?
Of course, this is unfair. Suppose the moon is immersed carefully in the magma. This would merely cause the earth's surface to expand a bit, leading to massive tectonic upheaval, but life perched carefully in the middle of relatively stable continental plates may be ok. Or suppose it's levitated carefully to just touch the bottom of the ocean but not fall any further. Assuming the moon is stable under its own gravity to hold together enough that no bits fall off in the Earth's gravity (which would result in a mess similar to scenario #1) This will merely cause a lot of nearby water and possibly mountains to fall sideways off the earth and onto the moon, causing more traditional world-wise Tsunamis that may be made of water rather than lava. In both cases, primitive biota and mammals cosying in mine shafts may be ok.
[1] And viruses, but bacteria need water and some useful chemicals to come back to life. Viruses need bacteria.
[2] I use the term "Tidal wave" despite the "tidal" being considered a misnomer. Despite the name, these waves are typically not being caused by the moon, which causes many pedants to prefer the more euphonious "Tsunami". However, as I have been at quite unnecessary pains to explain, the wave I'm discussing here IS caused by the moon. So I'm going to say the not-quite-correct "Tidal wave" in the hopes that bad pedants will be annoyed and good pedants will think it's funny.
[3] I have no justification for choosing the American proprietary term "Jello" rather than the British generic term "Jelly", but did so PURELY to annoy pedants. However, it occurred to me because it (1) sounds funnier and (2) suggests clearly that I'm referring to desert jelly, rather than royal jelly, petroleum jelly, gelignite, American-made jam, or any other anatomic, biological, lubricating or industrial substance which wobbles or has a similar technical name and picked up the descriptor "Jelly" somewhere along the line.