Our major planet ’s magnetic field is constantly change and evolving , making it unacceptable to screw how the field comport at any given stage in the past . The only real agency to canvass ancient magnetic attraction is through our ancestors ’ beloved of fire .
Paleomagnetism has had an incredibly important function in the history of geology , as it was enquiry into Earth ’s past magnetised fields that helped set up the existence and movement of the architectonic plates in the sixties and seventies . Paleomagnetic data continues to be crucial as a dating instrument for human settlement internet site and all form of fossil clay .
To ground an accurate paleomagnetic chronology , researcher trust on human pottery - fashioning . Such activities take firing mineral to temperature exceedingthe Curie Temperature , which is the point above which objects become demagnetized . When the target coolheaded , the finished pot remagnetizes , lock in in a criminal record of the direction and persuasiveness of the magnetic study in the region at that point in metre and quad .
This line of inquiry has yield fabulously precise data for much of the Northern Hemisphere , but the Southern Hemisphere is trickier — partially because so much of it is covered by ocean , but also some Pacific culture did n’t make pottery . The Maori , who first square up New Zealand around 1200 CE , are one such illustration of a culture that left behind no pottery and , seemingly , no paleomagnetic data point .
But the Maori are far-famed for hāngi , enceinte steam pit oven using heated rocks . As Dr. Gillian Turner of Wellington ’s Victoria Universityexplains to the BBC , ancient Maori folklore suggests the hāngi stone might well have been red-hot enough to go past the Curie temperature :
“ The Maori legend is that the Stone reach blanched hot heat . Well , scarlet hot is about 700 degrees and so clean raging would be a expert deal more than that . But by put some thermocouples in the stones we were able to show they got as mellow as 1,100 ampere-second , which of itself is quite surprising . At that temperature , rock candy - organise mineral start to become plastic if not melt . The Maori prefer these volcanic boulder because they do n’t crack and shatter in the fire , and from our point of view they ’re the best because magnetically they deport better – they ’re form with a gamy concentration of magnetic iron-ore . ”
Dr. Turner and her fellow researchers experimented with modern hāngi to confirm that the rock did indeed exceed the Curie temperature , which means that all rock from ancient hāngi site potentially apply a wealth of entropy on Earth ’s magnetic fields . By radiocarbon dating charcoal recovered at the hāngi sites , Dr. Turner can identify just when the careen were first fired . For more , check outthe full story over at BBC News .
Image by matteo.laghetto onFlickr .
ArchaeologyGeologyScience
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