Earth gave birth to the Moon

[mike3]

I made some calcultations with an axe and wood: it would take only 6 650 000 kg of 235U nuclei to fission to have an atomic explosion yield the total amount of energy cited (2,5*10^30 J) under same conditions as a human-made bomb. That is the mass of the fissioning nuclei put together, not the critical mass or the whole amount of uranium present at any particular place. Also some of that energy will not do work to put stuff to orbit to achieve the cited figure. It was just a fun exercise in scale.

That's got to be off. Even pure antimatter would require something like 13.9 trillion kg(!) of pure antimatter annihilated with an equal part of matter to produce that much energy. Uranium fission is like 1000 times less energy-dense than mass-energy equivalence, so I'd imagine it'd take more like 27 quadrilllion kg(!!!) of Uranium.

Doesn't seem to work. The giant impact theory, or some variation thereof, still seems like the best one.

 

[Sockor]

Yes of course i'm wrong.
Without the user-unfriendly Windows calculator i get so big a number i can't even count to: 2,8 *10^16 kg. Oup-la.

 

[Reactor drone]

Yes, I picked it up on the wike. Carbon 14 is 6 protons and 8 neutrons. Fear not. I got that far . If anyone has the patience to attempt to explain how the heck we are able to know this with complete precision I would appreciate it.

Isotope ratios of a sample can be measured with mass spectrometry. They basically work by stripping off the electrons from the elements and looking at how the positively charged nucleus behaves in an electromagnetic field. The nucleii of heavier isotopes have more momentum and land in a different part of the detector than the lighter isotopes.

http://en.wikipedia.org/wiki/Mass_spectrometry

 

[Reality Check]

Regarding the evidence of a molten surface, my understanding was that the impact theory (and I would assume, by extension, this one) occurred before the earth fully cooled, while the surface (or much of it) was still molten (or mostly molten). Thus, there wouldn't really be any indication of a molten surface.

Giant impact hypothesis

There remain several questions concerning the best current models of the giant impact hypothesis, however. The energy of such a giant impact is predicted to heat Earth to produce a global 'ocean' of magma; yet there is no evidence of the resultant planetary differentiation of the heavier material sinking into Earth's mantle.

The indications of a molten surface caused by the impact would be the formation of a heavier layer within the mantle.

The nuclear explosion theory implies that the Earth has cooled enough for a mantle to have formed because it is in the core-mantle boundary that the required concentration of fissionable material happens.

Likewise, the moon would have been around long enough for any surface features to be largely lost by meteorite impacts over time (or at least lost without an extensive survey of the surface).

That is correct but has little to do with the presence or not of a molten surface (which would not have any surface features!).

 

[anglolawyer]

Isotope ratios of a sample can be measured with mass spectrometry. They basically work by stripping off the electrons from the elements and looking at how the positively charged nucleus behaves in an electromagnetic field. The nucleii of heavier isotopes have more momentum and land in a different part of the detector than the lighter isotopes.

http://en.wikipedia.org/wiki/Mass_spectrometry

Thanks. Still baffling but it's as close as I'm likely to get.

 

[Hellbound]

Reality Check:

I see now. Didn't think about the melting allowing for differentiation of material by weight. That makes sense.

Thanks

 

[nathan]

Thanks. Still baffling but it's as close as I'm likely to get.

A heavier car will turn less sharply at the same speed as a lighter car, if you turn the steering wheel with the same force in each case. If you're turning into a wall, the cars will make holes in different places.

 

[anglolawyer]

A heavier car will turn less sharply at the same speed as a lighter car, if you turn the steering wheel with the same force in each case. If you're turning into a wall, the cars will make holes in different places.

It's the smallness of everything that bugs me. I understand what you said but just have a problem getting how it's possible to work out so much, down to precise numbers of protons etc, about atomic structures and the - 'yes but how do we know this?' - question nags and distracts.

ETA anyhow, referring back to the subject of the thread it doesn't appear from the discussion that the premise of the nuclear explosion theory is accepted anyway i.e. that the moon is made of the same stuff as the earth.

 

[Pixel42]

There's another new theory:

http://www.nasa.gov/topics/solarsystem/features/moon_formation.html

New research, funded by the NASA Lunar Science Institute (NLSI), hypothesizes that our early Earth and moon were both created together in a giant collision of two planetary bodies that were each five times the size of Mars.

This new hypothesis about how Earth’s moon formed is challenging the commonly believed “giant impact hypothesis,” which suggests that Earth's moon formed from a colossal impact of a hypothetical planetary embryo, named Theia, with Earth, early in our Solar System's history. [...]

After colliding, the two similar-sized bodies then re-collided, forming an early Earth surrounded by a disk of material that combined to form the moon. The re-collision and subsequent merger left the two bodies with the similar chemical compositions seen today.

The new model was developed by Robin M. Canup of the Southwest Research Institute (SwRI), San Antonio, Texas. Canup’s research was motivated by accompanying studies by other scientists on the early dynamical history of the moon, and accounts for this similarity in composition, while also yielding an appropriate mass for Earth and the moon.

 

[anglolawyer]

There's another new theory:

http://www.nasa.gov/topics/solarsystem/features/moon_formation.html

Presumably one can computer-model all this. I mean, what, start with a giant rotating cloud of dust and see what happens. Is that actually difficult to model?

 

[DC]

and the earth was a virgin, it's a miracle

 

[Hellbound]

and the earth was a virgin, it's a miracle

No, I think it was most probably penetrated. Only one of the competing theories has it being virgin