====== Earth’s magnetic field ======

Without the magnetic field, high energy radiation from space would affect the Earth's upper atmosphere much more dramatically – and high-energy radiation reaching the surface would be far higher. The levels of radiation //without// a planetary magnetic field would be so high as to profoundly alter the way life has evolved.

>In 1905, shortly after composing his special relativity paper, Albert Einstein described the origin of the Earth's magnetic field as being one of the great unsolved problems facing modern physicists."
>\\ Source : [[http://en.wikipedia.org/wiki/Dynamo_theory|Wikipedia]]

There maybe a gargantuan revolving molten iron outer-core – the so-called //Dynamo Theory// – but it’s known from magnetised ‘stripes’ in extruded seabed rock that the Earth’s magnetic field completely (and rapidly) reverses every 200,000 to 300,000 years. (see : [[https://en.wikipedia.org/wiki/Magnetic_anomaly#Ocean_floor_stripes|Wikipedia]] )

There is no clear theory as to how these geomagnetic reversals might have occurred. If the Earth does have an internal ‘Dynamo’ it would seem unlikely that it could spontaneously reverse its rotation, or turn upside down.

Recent calculations regarding the formation of the 'dynamo' conflict with geological evidence :

>Evidence is mounting that the dynamo could only have emerged comparatively recently. At the same time, geological clues show that the magnetic field has existed for most of Earth’s 4.5-billion-year history.
> \\ Source : [[https://www.newscientist.com/article/mg23331080-200-the-paradox-powering-earths-magnetic-field/|The paradox powering Earth’s magnetic field]] //New Scientist//, Jan 2017

A 2021 research project performed in New Zealand found that the last reversal was approx. 42,000 years ago. Noting that the global impact of such events "remains unclear"   See : [[https://science.sciencemag.org/content/371/6531/811|Science]] , Vol. 371, Issue 6531, pp. 811-818

==== Evolution of the field ====

The time at which the magnetic field first formed is unclear. Estimates vary from around 0.5 billion years ago to 4 billion. (Example paper : [[https://www.nature.com/articles/nature15523|Nature]]  volume 526, pages 245–248, 2015).

//Notes : //

1) There are many semi-permanent 'magnetic anomaly' areas around the globe, where the measured magnetic field has unexpected variations - a map is available from [[https://ccgm.org/en/maps/113-carte-des-anomalies-magnetiques-du-monde.html|CCGM.org]]

2) It's widely agreed that there is also a solid iron/nickel Inner Core - but that it's non-magnetic due to its extremely high temperature - around 5,430 °C.

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Also see : [[content:earth_sciences:earth_core]]

~~stars>3/5~~