European Salon de News, Discussion et Klatsch – 11 July | 84 comments (84 topical, editorial, 0 hidden)

I don't know much of his perceptions on climate change, but Allegre was a venerable giant in petrology.

As for this:

the magnetic field has been stable now for one of the longest periods in the history of the earth and is weakening like it did before previous inversions

Yes, it is weakening like what is seemingly happening before other inversions, but stable? The last inversion was (top of my head) some 800.000 years ago (Wikipedia check: 780.000 years). That's not particularly long, considering the 37 million years of the Cretaceous Long Normal Superchron. And during the past 780.000 years it doesn't look that stable to me...

by Nomad (Bjinse) on Wed Jul 11th, 2007 at 09:23:11 AM EST
[ Parent ]

Re: Allegre (4.00 / 2)

I meant: it did not reverse. before our stretch of 800k years, it used to reverse every 10-100k years for millions of years.

Pierre

by Pierre on Wed Jul 11th, 2007 at 09:30:39 AM EST
[ Parent ]

Okay (none / 1)

As long as we don't really know what causes reversals, that's still okay. It has been recognised that variations in the current period have a periodicity of 10 and 100k years. Apparently the field did not flip even during the variations. Yet is the internal motor of the magnetic field actually stable - who knows?

I -think- (danger Will Robinson danger!!!) it could work like flipping a coin: every time the dynamic destabilises it has a 50% chance of actually uprighting itself again (non-reversal) or the field turns over completely. If so, in the current period the field has destabilised previously but just never reversed.

by Nomad (Bjinse) on Wed Jul 11th, 2007 at 10:34:45 AM EST
[ Parent ]

Re: Okay (none / 1)

It flipped too many times back on the same side in the present chron. The coin has to be loaded...

Pierre

by Pierre on Wed Jul 11th, 2007 at 10:41:51 AM EST
[ Parent ]

Mmm (none / 1)

system could have internal resistance to change - what's the law called in thermodynamics... Then it's not a 50 - 50% chance.

Otherwise the question becomes: loaded with what?

by Nomad (Bjinse) on Wed Jul 11th, 2007 at 10:57:50 AM EST
[ Parent ]

Re: Mmm (none / 1)

I think the law is called "conservation of angular momentum".

Can the last politician to go out the revolving door please turn the lights off?

by Carrie (migeru at eurotrib dot com) on Wed Jul 11th, 2007 at 11:11:03 AM EST
[ Parent ]

Re: Mmm (none / 0)

yeah, that would tend to keep the dynamo pretty much upright all the time. It's dynamics law, no need for thermodynamics here. I don't think the whole problem involves any statistical mechanics here, just very complicated navier-stokes + heat generation and transfer + current loops. Probably as bad as plasma dynamics, and the PDE have solutions that are extremely sensitive to initial conditions, yet the stable dynamo is an attractor and all the chaos stuff that was trendy 15 years ago and everybody's jaded.

Pierre

by Pierre on Wed Jul 11th, 2007 at 11:16:21 AM EST
[ Parent ]

European Salon de News, Discussion et Klatsch – 11 July | 84 comments (84 topical, 0 editorial, 0 hidden)

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