Actual linkage between tectonic-mantle motions and lunar recession speeds?

[stargene]

Is there an overarching link between the fact that, on the one hand: (1)
plate tectonic motions range typically between a few mm/year to about
100 mm/year, & (2) mantle convection speeds average roughly around
"..20 mm/yr.." (wikipedia entry)...and on the other hand: (3) the Moon,
due to tidal effects, is "..spiraling away from Earth at a rate of 3.8 cm/yr
[or about 38 mm/yr...me] per year (wikipedia entry) ?

Ie: Can these very similar values all have a common origin--perhaps in the
mutual spin and tidal interactions of the Earth-Moon-Sun system? The usual
driver for mantle (and plate) motion is said to be due to the heat flow and
the local geochemistry of the Earth's interior, and of course the decay of
several radionuclides. Ie: Is this similarity between (1, 2) and (3)
merely a quirky coincidence? Or, over billions of years, have all three
processes achieved some mutual energetics 'partitioning' balance?

[[Mod. note -- It's a coincidence. -- jt]]

[Phillip Helbig (undress to reply)]

Post by stargene
Is there an overarching link between the fact that, on the one hand: (1)
plate tectonic motions range typically between a few mm/year to about
100 mm/year, & (2) mantle convection speeds average roughly around
"..20 mm/yr.." (wikipedia entry)...and on the other hand: (3) the Moon,
due to tidal effects, is "..spiraling away from Earth at a rate of 3.8 cm/yr
[or about 38 mm/yr...me] per year (wikipedia entry) ?
Ie: Can these very similar values all have a common origin--perhaps in the
mutual spin and tidal interactions of the Earth-Moon-Sun system? The usual
driver for mantle (and plate) motion is said to be due to the heat flow and
the local geochemistry of the Earth's interior, and of course the decay of
several radionuclides. Ie: Is this similarity between (1, 2) and (3)
merely a quirky coincidence? Or, over billions of years, have all three
processes achieved some mutual energetics 'partitioning' balance?
[[Mod. note -- It's a coincidence. -- jt]]

I agree with jt here. In cosmology, some people make much of apparently
unrelated quantities, for example the age of the universe and the Hubble
time (which means that, essentially, the decelerating and accelerating
phases cancel---more interestingly, they do so only now), or the energy
density due to matter and the cosmological constant. Coincidence or
something deeper?

Essentially, this means that two quantities are roughly equal, or that
their ratio is a very small (or, if the other way around, very large)
number. Other people claim that it is extremely small (or large)
dimensionless numbers which need explanation, not the other way around
(cue "naturalness"). (I tend to think that an equality needs an
explanation; if two things are unrelated, chances are that their ratio
will be a small (or large) number.)

The literature here is confusing, to say the least.

The angular size of the Sun and the Moon---which allows the corona to be
seen during a total solar eclipse---is also such an equality, but for
some reason most don't see it as significant (and, as noted above, the
Moon is receding from the Earth, so this equality holds only now).

What determines whether such an equality (or near equality) is
"interesting"?

The brightest stars, planets, and meteors are all about 0 mag. As far
as I know, this is just a coincidence. (At other locations in the
universe, this would not hold.) As Yogi Berra said, one can find a lot
of things by looking.

-------------------------------------------------------------------------------
Well, the trouble with coincidences is that sometimes they tell you something
and sometimes they don't.

---Mike Turner

[e***@gmail.com]

Post by stargene
Ie: Can these very similar values all have a common origin--perhaps in the
mutual spin and tidal interactions of the Earth-Moon-Sun system? The usual
driver for mantle (and plate) motion is said to be due to the heat flow and
the local geochemistry of the Earth's interior, and of course the decay of
several radionuclides. Ie: Is this similarity between (1, 2) and (3)
merely a quirky coincidence? Or, over billions of years, have all three
processes achieved some mutual energetics 'partitioning' balance?
[[Mod. note -- It's a coincidence. -- jt]]

Earth core heating can be stated as an effect of Sun/Earth/Moon
gravity tidal effects. This effect is seen in comet core heating
as it passes near the sun. The core of the comet heats before
the surface does.

So if tidal heating is real, the moon certainly be said to
effect the Earth core heating. And core heating then could be
said possibly altering mantle state.

Star to star tidal heating would then be seen as a dark matter
effect. Begging the question of observing dark matter in this
solar system.

[Phillip Helbig (undress to reply)]

Post by e***@gmail.com

Post by stargene
Ie: Can these very similar values all have a common origin--perhaps in the
mutual spin and tidal interactions of the Earth-Moon-Sun system? The usual
driver for mantle (and plate) motion is said to be due to the heat flow and
the local geochemistry of the Earth's interior, and of course the decay of
several radionuclides. Ie: Is this similarity between (1, 2) and (3)
merely a quirky coincidence? Or, over billions of years, have all three
processes achieved some mutual energetics 'partitioning' balance?
[[Mod. note -- It's a coincidence. -- jt]]

Earth core heating can be stated as an effect of Sun/Earth/Moon
gravity tidal effects.

That certainly plays a role. However, the Earth is heated by
radioactivity to a significant extent as well.

Post by e***@gmail.com
This effect is seen in comet core heating
as it passes near the sun. The core of the comet heats before
the surface does.

Even if it is true that the core heats up first, is it clear that it is
due to tidal heating?

Post by e***@gmail.com
So if tidal heating is real, the moon certainly be said to
effect the Earth core heating. And core heating then could be
said possibly altering mantle state.

Right, but the observation of the original poster is still a
coincidence.

Post by e***@gmail.com
Star to star tidal heating would then be seen as a dark matter
effect.

While it certainly exists to some degree, appreciable perhaps only
in close binary systems, it is unclear what this has to do with dark
matter.

Post by e***@gmail.com
Begging the question of observing dark matter in this
solar system.

You probably mean "ask" the question rather than "beg" the question.
("Begging the question" means answering a question in such a way that it
merely rephrases the original question.) So you are saying that if
star-to-star tidal heating is somehow responsible for effects which are
usually attributed to dark matter, then these might not be observable in
the Solar System? Note, though, that, depending on what it is, dark
matter might not be uniformly distributed, and lack of such observations
in the Solar System don't prove that it doesn't exist, much less prove
the star-to-star---tidal-heating hypothesis.

[Bruce Scott]

On 2018-08-20, Phillip Helbig (undress to reply)

Post by Phillip Helbig (undress to reply)

Post by e***@gmail.com
Earth core heating can be stated as an effect of Sun/Earth/Moon
gravity tidal effects.

That certainly plays a role. However, the Earth is heated by
radioactivity to a significant extent as well.

The text by W Hubbard on Planetary Interiors notes that the Earth has
an unusually large dissipation coefficient for tidal dissipation and
suggests a lot of it is in the surface or near surface layers. Tidal
motion of the oceans (main sloshing period about 40 hours, compared to
the 24 hr rotation... IIRC originally noted by Laplace) seems to have
a big effect. The discussion suggested that not a lot of the tidal
effects in the Earth have to do with the core.

Quesiton about the radioactive heating: is it more Potassium 40 in the
deep core anyway (I thought the heavy U or Th stuff was closer to the
surface, maybe outer mantle)?

[Richard D. Saam]

Post by Phillip Helbig (undress to reply)

Post by e***@gmail.com

Post by stargene
Ie: Can these very similar values all have a common origin--perhaps in the
mutual spin and tidal interactions of the Earth-Moon-Sun system? The usual
driver for mantle (and plate) motion is said to be due to the heat flow and
the local geochemistry of the Earth's interior, and of course the decay of
several radionuclides. Ie: Is this similarity between (1, 2) and (3)
merely a quirky coincidence? Or, over billions of years, have all three
processes achieved some mutual energetics 'partitioning' balance?
[[Mod. note -- It's a coincidence. -- jt]]

Earth core heating can be stated as an effect of Sun/Earth/Moon
gravity tidal effects.

That certainly plays a role. However, the Earth is heated by
radioactivity to a significant extent as well.

Lord Kelvin(1824 - 1907) did not have the radioactivity concept
available to him
(he did not believe Marie Curie's 1867- 1934 radioactivity)
and thermodynamically predicted the earth's age at 20-200 million years
(off by factor of thousands).
RDS

[Phillip Helbig (undress to reply)]

Post by Richard D. Saam
Lord Kelvin(1824 - 1907) did not have the radioactivity concept
available to him
(he did not believe Marie Curie's 1867- 1934 radioactivity)
and thermodynamically predicted the earth's age at 20-200 million years
(off by factor of thousands).

Even 20 million to 4 billion is a factor of only 200. Yes, he was very
wrong, but not by a factor of thousands.

In his famous estimate of the age of the Earth, he did include the
caveat "unless another source of energy is found", as, indeed, it was.

[stargene]

Post by stargene
Is there an overarching link between the fact that, on the one

....

Okay, I can understand how the closeness between mantle/plate
motion and lunar recession motion can be a coincidence. Nothing
suggests otherwise apparently. It does seem to me that a check
might be to compare their respective motion rates in the deep
geophysical past--Say, over two billion years or so--One would
somehow need to detect fossil plate-motion speeds, probably
using proxies. Additionally, could one reliably constrain lunar
recession speeds over the same intervals? Ie: If it then appeared
that the two different motions were close over the Earth's age,
it might suggest a coupling. But again, a plausible
coupling mechanism would be needed, to consider linkage to be
not merely circumstantial. I don't know if current geophysical
techniques would reasonably support such a search.

[[Mod. note -- Alas, I don't think we have experimental data giving
either of those rates at any time other than "now". So any estimates
for gigayears in the past are going to be heavily dependent on
theoretical models of the underlying dynamics.

There are then two possibilities:
* If you think the the models are basically ok, then it's obvious that
the plate-tectonic and lunar-orbit-evolution rates are independent.
* If you don't think the models are basically ok, then you probably
shouldn't trust their estimates of either rates in the distant past.
-- jt]]