what is the evidence for geomagnetic reversal ?

billiards

Yes I do.

Why do you ask?

rogerharris

thanks geo. good clear explanation again. My inner Colombo feels at rest (for a while). I am guessing he will start coming out to play when I get into magnetohydrodynamics properly. I know from biophysics there is a lot of reaction diffusion going on in MHD.

Ok im not getting into that today

rogerharris

well actually im interested in this as well. I mean i speed read and downloaded a lot of the papers and tomes i could get which are inked here, and was still trying to find that one conclusive ocean striping study or meta analysis.

I expected it would be something like this.

Geologists dig down and take a dozen deep crust samples from south to north pole with the sample rod marked with its compass points. These are all time synchronized and labeled, so a clear picture emerges with no doubt that the field has flipped 180 degrees across the polar axis on all the samples.

I still cant find this. Any pointers as to the seminal work which makes it undoubtedly clear ?

Dotini

Well, I was trying to avoid the necessity of explaining global geomagnetic reversal, hoping to associate sea-floor striping with local tectonic anomalies, similar to Etruscan vases and Israel copper slag. But you are definitive, and I appreciate that very much.

Respectfully,
Steve

Evo

It's an established science, I'm not sure exactly what you're looking for.

Anyway for those with an interest

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

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

And a discussion of where paleomagnetism is used for dating.

http://archserve.id.ucsb.edu/courses...rchaeomag.html

geo101

Much of the seminal work is old, some going back over 100 hundred years. I would recommend reading through the book chapters that I suggested in post #23. First, they will give you a good overview of the weight of evidence. Second they will have most of the references that you are looking for. Essentially you are looking for papers like Matuyama (1929), who developed the first (albeit crude) global polarity timescale (GPTS, wiki/google search this). Or others like Kent & Gradstein (1985) or Kent and Olsen (1999)


Matuyama, M. (1929), On the direction of magnetisation of basalts in Japan, Tyosen and Manchuria, Proc. Imp. Acad. Jap., 5, 203-205.

Evo

BTW, welcome to the forum geo101!!!

geo101

Cheers

rogerharris

Ok thank. ill try and dig that up. The uni didnt have that book and google omits chapter 4. Im wary of forking out my grant if its not going to provide a specifically overwhelming case. I reckon i might know the seminal paper actually. if its overwhelmingly good i wont be back !

rogerharris

At last one paper where they take a load of samples across the entire earth, say what, 60 samples would be good i suppose to eliminate the errors but 20 would stll be something.

They then aggregate the samples and overwhelmingly find at least one reversal happening across the planet from north to south pole at the same time.

I havent found such a paper yet, but i think it does exist and know somebody who can tell me where to find it :)

I have been vey surprised that others do not demand to see at least this baseline of evidence to consider reversal a credible theory.

geo101

Valet et al., 2005

I'll write a better description in the morning. This is as "overwhelming" as you will get. What you have to remember is that establishment of geomagnetic reversals did not happen with one paper, but with hundreds of global records over a long period of time. The discovery of seafloor spreading and associated magnetic anomalies was the final nail in the coffin as it were.

rogerharris

thanks ill see if i can get that. Nature articles are hard to get even at british universities.

billiards

I've been away the past few days.

Geo101 seems to have the references more or less covered.

I would like to add this paper which charts a whole reversal over a time period constrained to be 4,500 to 11,200 years.


CLEMENT and KENT. A DETAILED RECORD OF THE LOWER JARAMILLO POLARITY TRANSITION FROM A SOUTHERN-HEMISPHERE, DEEP-SEA SEDIMENT CORE. JGR (1984) vol. 89 (NB2) pp. 1049-1058

billiards

So because I believe the evidence you stop thinking?

I might be a "crank" or a "fool" or perhaps neither but still simply "wrong". Follow your own mind, convince yourself.

Now you have got me interested in the Etruscan vases and the Israel copper slag. I do not know anything about those.

Evo

Roger, this is a brief history with tons of references.

http://www.irm.umn.edu/quarterly/irmq20-3.pdf

geo101

Errr... is it morning??
Better late than never.

So one thing that we didn't talk about so far is how the strength of the field changes as the field reverses. All of the available data tell us that the main dipole field drops to about 20% of it's pre-reversal strength. Again this is seen at various times and across the globe.

The Valet paper stacked together relative paleointensity (geomagnetic field strength) records over the past 2 million years from 10 globally distributed deep sea sediment core, essentially confirming that the lows associated with reversal are a global feature.


Evo - good catch on the IRM Quarterly, I miss that one