The Significant Kauri Tree.
During my forestry days, I used chain and compass surveys to plot areas of interest onto a map. The principle was to start at a known surveyed point, usually surveyed by a theodolite, but not necessarily, and finishing at the same or another known or accepted point. If it doesn’t work out or ‘close’ on the map, something has gone wrong; the two most likely reasons are misreading the compass or ‘errors in tabulation’, which was the term for writing the compass reading down inaccurately. A prismatic compass points to magnetic north, not true north and magnetic north has a habit of moving slightly from time to time, so to check what the magnetic declination was, I compared my reading of two trig points that the famous (in New Zealand and Singapore) surveyor John Turnball Thomson had established circa 1860 with a theodolite. So, another reason for surveys failing to close was the wandering magnetic declination, which is why I always checked the magnetic declination before starting my surveys.
With that in mind, I’ve often pondered about the scare stories of the Earth’s magnetic field reversing, which led me to wonder about a tiny blue ball spinning around in space, and who says what’s up and what’s down? Sure, the equator is where the sun’s rays hit the most… but there’s no scientific law for north to be north, it’s just a matter of historical convention. Anyway, to my surprise, according to an article an old forestry mate sent me, the magnetic field did reverse 42 000 years ago, and later changed back to its present location. The change took about 800 years – 200 to reach reversal with 400 years of reversal and then another 200 to return. Apparently, it has happened before but the 42 000 years ago event has been proven by an ancient Kauri tree that grew in New Zealand.
Kauri trees live to a good age; they have a clean bole and then branch out with heavy branches. The largest live specimen is around 2000 years old and has a diameter at breast height of five metres. Logging Kauri is no longer allowed, but when it was legal there were bigger specimens; I remember a tale of couples dancing on a large stump but the number eludes me… if I had to take a punt, it would be 46. Kauri trees have a long lifespan, and after maturity they begin the process of dying, which may go on for 4 to 600 years, but eventually they die and remain standing for… well your guess is as good as mine, but eventually they fall and this one was preserved in a peat bog. There is an industry of digging in peat to find Kauri remnants, which are used for fine furniture and this one was dug up in 2019. I don’t like the industry, but at least this tree found its way to a laboratory.
The tree had lived through the Laschamp excursion which is what this particular magnetic field shift has been called, and an analysis of the tree rings revealed spikes in atmospheric radiocarbon levels, a signature of a weakening magnetic field, which, during the excursion was 28% of what it is today. During the transition times it was down to 6%! The effects were worldwide and together with or because of, the poles iced over and there were shifts in wind patterns and tropical storms. The magnetic field deflects incoming cosmic rays, and in this case caused climate shifts bring droughts in Australia, which were responsible for an extinction of Australian megafauna at the time. At the same time the demise of Neanderthals happened and cave art began due to the human retreat into caves for protection.
It turns out that the scare stories do have a point; we don’t want the magnetic field to wander off too far, but we don’t know what would trigger it or if it could be prevented. Given the transition period is a couple of hundred years adaption of some kind is possible, but we couldn’t be able to live as we do today. The magnetic field maintains the atmospheric balance… Mars has no magnetic field, which might be an indicator. Migratory animals rely on the magnetic field for navigation as mankind has done in the past although GPS might work if the satellites don’t tumble to Earth or go out of kilter. Technology and communication would also be impacted because geomagnetic storms that would occur causing electrical grids to fail.
It turns out that Earth’s magnetic field is pretty important, and I like the idea of a New Zealand tree helping the research into what the likely impacts of a magnetic field shift might be. I know the world could do with a good shakeup, but finding ways to get on with our neighbours is surely a better option than waiting for it to happen.
