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back to article Kiwi archaeologists cook up a record of Earth’s magnetism

A kind of oven used by the Maori since long before Europeans arrived in New Zealand is being mined for archaeological information about the history of Earth’s magnetic fields. Scientists from Victoria University in Wellington, New Zealand, say that there’s a gap in the global palaeomagnetic record in the south-west Pacific, and …

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Holmes

Another payout

Does this mean Maori's are aligned to the Earths magnetic field via Hangi pits?

Another Treaty of Waitangi payout at the tax payers expense coming up...

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Flame

Just a wee tip for Pakeha reading this from outside Aotearoa. It's pronounced "Hungy" rather than "Hangy".

Hope that helps.

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Anonymous Coward

Not really

We're quite capable of guessing that 'a' more likely corresponds to a normal, international /a/ rather than a weird English/Kiwi /æ/, so it would be more helpful to tell us how to pronounce the 'ng', which could quite easily be /ŋ/ or /ŋg/ (like the difference between "singer" and "finger").

Attempts to explain pronunciation using English spelling are not usually very successful.

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Anonymous Coward

According to the occasionally accurate Wikipedia

The time spans of Earth's magnetic field reversals are randomly distributed, with most being between 0.1 and 1 million years, with an average of 450,000 years. Most reversals are estimated to take between 1,000 and 10,000 years. The latest one, the Brunhes–Matuyama reversal, occurred 780,000 years ago.

Current opinions on the consequences of magnetic field reversals range from there is no convincing evidence that magnetic field reversals have serious repercussions to they are associated with mass extinctions.

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Thumb Up

They have been doing this with campfires in Australia since the 1960's...

... covering a period of at least 30,000 years. The idea isn't new but only going back 500 to 700 years might be. Neat.

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Boffin

Not quite sure what the excitement is about...

It seems that 500-700 years ago there would not have been any polar drift, so I am not sure what the value of this would be.

There is a mountain in Oregon (who's name I forget), which is made up of eroded volcanic fissure eruption lava flows laid out in hundreds of several-foot-thick sheets over the course of hundreds of thousands of years. Thats shown some interesting results, including the magentic poles differing between rocks at the top of one layer and the bottom of the same layer. So the top of the lava flow cools and forms a crust with one magnetic orientation, and the bottom cools some days later and forms with the opposite magnetic orientation.

So polar drift can occur in the space of a few days when things are really unstable.

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Re: Not quite sure what the excitement is about...

Even over a 500-700 period the poles slowly drift, and there are also magnetic anomalies that randomly appear in certain areas that are believed to be linked with the local flow of material (liquid iron in the core, magna in the mantle, whatever) under the crust. So there is something that can be learned even when we know the poles haven't reversed over human timescales.

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Joke

Re: Not quite sure what the excitement is about...

The excitement? That'd be because the Kiwis have found an excuse for a hangi and calling it "work" ...

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Rift zones, anyone?

Isn't there a 180 million year[1] continuous record of the Earth's magnetic field in the North Atlantic? And a similar record in NZ's volcanic record? What's the point of this research? I smell graft ...

[1] Exact age from memory ...

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Re: Rift zones, anyone?

Yes, however the magnetic field orientation isn't consistent across the whole globe.

At the very least it wobbles up and down, but there is also sideways movement.

So it's useful to know the historical orientation at as many points on the surface as we can.

As to a real-world use, there are databases of how it varies "locally" at the moment that are used by smartphones and drones, it would be useful to know how often those will need updating.

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Re: Rift zones, anyone?

'Isn't there a 180 million year[1] continuous record of the Earth's magnetic field in the North Atlantic? And a similar record in NZ's volcanic record? What's the point of this research? I smell graft ...'

The recent magnetic history of the Northern Hemisphere is well measured because there are huge numbers of industrial sites and pottery kilns going back thousands of years. The Southern Hemisphere is much less well understood because those technologies didn't develop nearly so much.

As for magnetic records, the North Atlantic is only about 50My, the oldest ocean floor is located in the Western Pacific off of Japan and the Philippines and is as you say about 180My.

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Ground Movement

How useful would this data be?

These stones have been underground and since you know earthquakes and plate movement etc. cause this to move, would this cause the data to be wrong?

I could jest be showing my lack of knowledge on these subjects here but dear with me.

For example:

Rock is in oven being heated, rock gets very hot. Rock bits align to magnetic field, rocks move when cooling, earthquake a happens and rocks move more after earthquake a. Earthquake b happens, rocks move even more.

Would this affect how they think the alignment was at that time or do they have ways of dealing with this?

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Re: Ground Movement

And for the grammar pedants I apologise for the above post.

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Re: Ground Movement

You're bang on the mark. Any movement of the rocks could throw up errors in magnetic inclination and declination. Any signs of seismic disturbance of the site and you'd have to exclude it from your sample, so you have to be absolutely sure the rocks are in situ and haven't moved since the last moa was thrown on the barbie.

Where they could be really useful is plotting movements of different slices of New Zealand across fault zones. As the faults move the alignment of contemporary barbecues would differ allowing you to trace the movements of the fault through time.

And if you thought this was odd, I once met a biologist who was tracking the movement of the San Andreas fault through time by measuring differences in the genomes of weevil colonies.

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