Earth's core

[tkdguy]

http://news.yahoo.com/s/ap/20050825/ap_on_sc/earthspin

 

It seems like the Earth's core is spinning more quickly than its crust.

[austenandrews]

Re: Earth's core

 

[McCoy]

Re: Earth's core

 

OK, courtesy of The Daily: "Today President Bush insisted that schools who taught this should also present the alternative theory, that Hell has a Merry-Go-Round."

[McCoy]

Re: Earth's core

 

Seriously, assuming that a year has always been as long as it is now, fossil evidence shows that solar days and lunar months have been getting longer. Most likely tidal braking has transfered angular momentium from the Earth, making the crust spin slower, to the Moon, making it orbit further from Earth and making the lunar month longer. Since the solid inner core is suspended within the liquid puter core, it tales a while for firction to slow the core to the same speed as the crust, by which time it is spinning slower.

[Dr. Anomaly]

Re: Earth's core

 

Seriously' date=' assuming that a year has always been as long as it is now, fossil evidence shows that solar days and lunar months have been getting longer. Most likely tidal braking has transfered angular momentium from the Earth, making the crust spin slower, to the Moon, making it orbit further from Earth and making the lunar month longer. Since the solid inner core is suspended within the liquid puter core, it tales a while for firction to slow the core to the same speed as the crust, by which time it is spinning slower.[/quote']

That's the current best theory, IIRC. I mean -- they have documented, with modern instruments, that the moon is moving further away, just very, very gradually. Ditto the gradual increase in the day, and physics says the two are directly related.

 

Re: friction vs. the core, that's also true, but it's not the whole story. Don't forget there's also magnetic coupling involved.

[McCoy]

Re: Earth's core

 

Re: friction vs. the core' date=' that's also true, but it's not the whole story. Don't forget there's also magnetic coupling involved. [/quote']

Good point. And we may be overdue for a field shift.

[Cancer]

Re: Earth's core

 

Good point. And we may be overdue for a field shift.

 

There are a number of suggestions that we are in the process of a polarity reversal now. We know such things happen "quickly" by geophysical time, but that doesn't say much when compared to human timescales.

 

I've read a couple of decent articles, in the last year or so on the problem of MHD and figuring out what's going on with the Earth's magnetic field. It's a nasty computational problem.

 

Right now, at least, the Moon is receding on average at about 4 cm per year. You have to take a long-term time average to get that; the Moon's orbit is elliptical and precessing and nutating and all sorts of other cyclic and quasi-cycling things, so at any given moment its velocity will be different from that.

[austenandrews]

Re: Earth's core

 

I wonder what the effects will be of a pole reversal?

[Dale A. Ward]

Re: Earth's core

 

I wonder what the effects will be of a pole reversal?

 

Australia can celebrate a white Christmas...

[McCoy]

Re: Earth's core

 

I wonder what the effects will be of a pole reversal?

Best case: We have to repaint the needles in the compases.

 

Worse case: End of citilization as we know it.

[Cancer]

Re: Earth's core

 

I wonder what the effects will be of a pole reversal?

 

For a while the Earth's magnetic field will not be a simple dipole field like we're used to. It will be much weaker, and a more complicated geometry.

 

This will naturally bollix up magnetic navigation, of course. I wonder what happens to migratory wildlife that use the geomagnetic field when this happens. I'm not really worried ... this type of event happens "frequently" over Earth's history, so it's not like all the ducks will get lost or anything ... just curious.

 

For a while, the magnetosphere will be rather weaker. This means more of the charged particle flux from the Sun -- the "solar wind" -- will hit the upper parts of the atmosphere. This is likely to mean many more auroras world-wide. It is also likely to mean increased radiation exposure to everyone. (This is going to be a modest effect relative to anthropogenic exposures, though.) Also to everything, though it is unclear how much impact this will have. A lot depends on how long it lasts.

[austenandrews]

Re: Earth's core

 

This will naturally bollix up magnetic navigation' date=' of course. I wonder what happens to migratory wildlife that use the geomagnetic field when this happens. I'm not really worried ... this type of event happens "frequently" over Earth's history, so it's not like all the ducks will get lost or anything ... just curious.[/quote']

That's the kind of thing I was thinking of. Frequent pole shifts must surely be accounted for in evolutionary terms. While migratory ducks won't suddenly fly in circles, I do wonder if they might redistribute a bit. Branch out to new places. Makes sense, in a way.

 

For a while, the magnetosphere will be rather weaker. This means more of the charged particle flux from the Sun -- the "solar wind" -- will hit the upper parts of the atmosphere. This is likely to mean many more auroras world-wide.

Hey, that's right! I hadn't thought of that. *****in'.

 

Also to everything, though it is unclear how much impact this will have. A lot depends on how long it lasts.

The biggest impact will surely be on us squishy life forms and our constructs. Confused compasses? No big deal. Greatly increased satellite attrition? Could conceivably get ugly.

[austenandrews]

Re: Earth's core

 

Worse case: End of citilization as we know it.

That happens about every ten years or so anyway, doesn't it?

[McCoy]

Re: Earth's core

 

That's the kind of thing I was thinking of. Frequent pole shifts must surely be accounted for in evolutionary terms. While migratory ducks won't suddenly fly in circles' date=' I do wonder if they might redistribute a bit. Branch out to new places. Makes sense, in a way.[/quote']

AFAIK no extinction event coincided with a pole reversal. Don't know if anyone has studyed mass migrations/redistribution with an eye toward coorlating them with pole shifts.

[Ben Seeman]

Re: Earth's core

 

And you people laughed at The Core! Shame on you!

[McCoy]

Re: Earth's core

 

Right now' date=' at least, the Moon is receding on average at about 4 cm per year. You have to take a long-term time average to get that; the Moon's orbit is elliptical and precessing and nutating and all sorts of other cyclic and quasi-cycling things, so at any given moment its velocity will be different from that.[/quote']

How sure are you of those figures? 4 meters a century sounds too large by at least two orders of magnitude.

[Dr. Anomaly]

Re: Earth's core

 

How sure are you of those figures? 4 meters a century sounds too large by at least two orders of magnitude.

The recession rate is about 38 mm per year, and the length of our day increases by about 15 µs per year.

 

Keep in mind those are the current rates, but the rates are not constant over time, so you can't do a simple linear projection to see how close the moon was at x time in the past, or will be at y time in the future. It's a bit more complicated than that.

[bigdamnhero]

Re: Earth's core

 

Best case: We have to repaint the needles in the compases.

 

Worse case: End of citilization as we know it.

 

Well, I'm glad we've got *that* bracketed.

 

 

bigdamnhero

“Your brain is like the four-headed man-eating haddock-fish-beast of Aberdeen.â€

“In what way?â€

“It doesn’t exist.â€

[McCoy]

Re: Earth's core

 

The recession rate is about 38 mm per year, and the length of our day increases by about 15 µs per year.

 

Keep in mind those are the current rates, but the rates are not constant over time, so you can't do a simple linear projection to see how close the moon was at x time in the past, or will be at y time in the future. It's a bit more complicated than that.

BUT as the distance from Earth center to Moon center decreases, the moon's gravity pull on the Earth, the tide effect, decreases, slowing the transfer of angular momentum. So historically the recession rate would have been higher.

 

(Humm, how does mean sea level affect this, recession higher in ice ages, when there is more shore for the tides to catch on, or in periods of global warming, when more water is available to move around? Or does the mass of the atmosphere make sea level irrelivant?)

 

Haven't checked the numbers, but 12-13 feet a century still sounds too big.

[Cancer]

Re: Earth's core

 

BUT as the distance from Earth center to Moon center decreases, the moon's gravity pull on the Earth, the tide effect, decreases, slowing the transfer of angular momentum. So historically the recession rate would have been higher.

 

(Humm, how does mean sea level affect this, recession higher in ice ages, when there is more shore for the tides to catch on, or in periods of global warming, when more water is available to move around? Or does the mass of the atmosphere make sea level irrelivant?)

 

Haven't checked the numbers, but 12-13 feet a century still sounds too big.

 

I'm quite confident of that "about 4 cm/year" number. I didn't do that measurement, but I know some of the guys who did. It turns into a fractional orbit size change of 10^-10 yr^-1. If you take the stupidest possible extrapolation, that means the orbit of the Moon has roughly doubled in size over its history. That's close enough to the right ball park that it makes sense. If anything, it must have slowed down over time, if the Giant Impact Hypothesis for the Moon's origin is correct, in which case it must have formed not too far outside the Roche limit.

 

I don't have a handle on how tides affect mean sea level changes. I read something recently (almost certainly in Physics Today) that local sea level changes can be strongly affected by isostatic rebound. Most of Scandinavia in particular is rising, still recovering from the removal of the overlying weight of the last ice sheet. That effect must at some level make it more difficult to interpret sea level changes.

[theltemes]

Re: Earth's core

 

According to NASA:

 

Recession rate from Earth (cm/yr): 3.8

[McCoy]

Re: Earth's core

 

Should have gotten back to this sooner, but was distracted by katrina threads.

 

Cancer, Dr. Anomaly, theltemes, you're right and I was wrong, 38 mm a year it us, which is a lot of force! If we could somehow tap that stream, no need to worry about imported oil.

[Dr. Anomaly]

Re: Earth's core

 

Should have gotten back to this sooner, but was distracted by katrina threads.

 

Cancer, Dr. Anomaly, theltemes, you're right and I was wrong, 38 mm a year it us, which is a lot of force! If we could somehow tap that stream, no need to worry about imported oil.

Hey, no problem McCoy. After all, it does sound like a lot, doesn't it? (I had to double-check the figures myself when I first found out.) And, when you consider the total energy involved, it is a lot...from the human perspective, anyway. Makes anything we've done yet seem tiny, yet in many ways it's the equivalent of "waste heat". Which is to say, a mere by-product, a scrap, a side effect.

 

And you're absolutely right...if we could figure out a way to harness that...geeze.

 

Funny, isn't it...the universe surrounds us with a plethora if "wasted" energy types/sources, any one of which, if we could find a way to harness it, would end our energy problems for centuries to come, even at the wildest possible growth rate imaginable.

 

And yet, so far we haven't had a good idea as to how to do it for one of them. (sigh)

[Dr. Anomaly]

Re: Earth's core

 

Oh, and just for reference, since it has been mentioned...

 

Mass of the atmosphere: about 5.1 × 10^18 kg

 

Mass of the oceans: about 1.4 × 10^21 kg

 

So the oceans outmass the atmosphere by about 3 orders of magnitude.

[McCoy]

Re: Earth's core

 

Oh, and just for reference, since it has been mentioned...

 

Mass of the atmosphere: about 5.1 × 10^18 kg

 

Mass of the oceans: about 1.4 × 10^21 kg

 

So the oceans outmass the atmosphere by about 3 orders of magnitude.

Thank you! So Mean sea level is a factor.