Ayooshi Mitra, Amity University, Kolkata
A long time ago, a record of the “lost time” was discovered by some workers digging grounds for a power plant in New Zealand. The discovery was of a 60-ton trunk from a kauri tree (the largest species of trees in New Zealand). The tree was assumed to have been grown 42,000 years ago and its rings crossed 1700 years, which seems to capture a time when the world was known to be “upside-down”.
According to the team of researchers who conducted this study, it was confirmed by modeling the effect of the radiation on the atmosphere, that the earth’s climate had shifted slightly, which may have been the reason for the disappearance of large mammals in Australia and Neanderthals in Europe.
The study not only pins the timing and magnitude of the magnetic swap, the latest in Earth’s history but is also one of the first to make a valid, though based on speculation, a case that these flips can impact the global climate. The magnetic field of the Earth is created by the outer core flow of molten iron, which is susceptible to chaotic swings that not only weaken the field but also cause the poles to wander and sometimes flip completely.
Long-lasting reversals are recorded by the magnetic orientations of minerals in rock but cannot capture the details of flip lasting hundreds of years, like the one 42,000 years ago. These shorter fluctuations can be marked by radioactive carbon-14, however. If cosmic rays slip past the magnetic field and strike the atmosphere, the isotope is generated. Living things take it up, and its half-life makes it a standard clock.
To date the kauri wood, the team utilized radiocarbon by lining it up with precise, but coarse, radiocarbon cave records from China. And they tracked how its production varied over 40-year intervals, as the magnetic field abated and surged, by measuring finer carbon-14 changes in the rings. Radiocarbon spikes showed that the magnetic field weakens 41,500 years ago to about 6 percent of its current strength. The poles flipped at that point and the field regained some strength 500 years later, before crashing and flipping back. Evidence from the ice core indicates that the sun experienced several “grand minima,” which is episodes of low magnetic activity, around that time. In the subtropics, the developed cosmic ray attack charged the airspace to a degree that would have resulted in today’s power grid and created auroras.
Also read:What does Ocean Warming mean for Tropical Rainfall?
Source:
Paul Voosen.,(2021), “Ancient kauri trees capture last collapse of Earth’s magnetic field”, Science, doi:10.1126/science.abh1456 https://www.sciencemag.org/news/2021/02/ancient-kauri-trees-capture-last-collapse-earth-s-magnetic-field
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