A few years ago, workers in New Zealand excavated a testimony from a forgotten time at the construction site of a new power plant: the 60-ton kauri tree trunk is the largest of New Zealand’s tree species. It grew 42,000 years ago. He was kept swamp. Its tree rings span over 1,700 years, thus a turbulent period in which the world has been turned upside down – at least magnetic.
Measurements in this and other pieces of wood indicated an increase in radiation from space at the time, due to the collapse of the Earth’s protective magnetic field and the reversal of the magnetic poles. This is what a team of scientists said In a recent study In the journal Science Science. According to their model account, the radiation would have disturbed the atmosphere to such an extent that the Earth’s climate was for a while outside the joint. “We’re just scratching the surface of what the geomagnetic change has done,” says Alan Cooper, an ancient DNA researcher at the Museum of South Australia and lead author.
Not only does the study detail the timing and extent of magnetic field change – the very latest in Earth’s history – but it also credibly argues that such changes could affect the global climate, says Quentin Simon, a paleomagnetic scientist at the European Center for Research and Education in Environmental Geosciences (CEREGE) In Aix-en-Provence, France. However, other paleoclimatologists are skeptical of the team’s far-reaching conclusions.
The magnetic field has weakened to six percent of the strength of the day
Earth’s magnetic field is formed by the flow of molten iron into its outer core. This is subject to chaotic fluctuations, which not only weaken the magnetic field but also cause the poles to move and reverse completely at times. The magnetic orientation of the minerals in the rock samples testifies to very slow field reversals, but it does not provide any information about a pole change that only lasted a few hundred years – like that of 42,000 years ago. However, the C14 carbon isotope can indicate these shorter fluctuations. An isotope is created when charged particles from space penetrate the Earth’s magnetic field and strike the atmosphere. Plants and other organisms build them into their tissues as they grow. Cooper’s team used the radiocarbon method to track a tree’s fossil how the isotope content changed as the magnetic field receded and became stronger again.
The increase in C14 concentration in the annual rings of the Kauri tree indicates that the magnetic field has weakened 41,500 years ago to six percent of its current strength. At this point the poles reversed and the field recovered somewhat before collapsing again and returning 500 years later. Not only did the Earth’s radiation shield drop, but the sun also fell, says co-researcher Alan Cooper. Evidence from ice core samples indicates that around this time the Sun passed through some “solar minimum” – phases of low magnetic activity. The resulting cosmic radiation storm had severely charged Earth’s atmosphere. Such bombing, Cooper says, would cripple today’s electricity grids and create the northern lights in the subtropics.
The team investigated the consequences of rapid pole changes using a climate model. The results indicate that the cosmic bombing led to the decomposition of the ozone layer. Thus, UV rays had a freer path, as wind currents mixed at great altitudes and led to drastic changes to the Earth’s surface. That would have included warmer North America and cooler Europe, says Marina Friedel, a stratospheric chemistry doctoral student at ETH in Zurich and co-author of the study.
Events in human history do not completely coincide with a magnetic field reversal
At this point, the study becomes very speculative, as other scholars criticize. Ice samples from Greenland and Antarctica, for example, which cover the past 100,000 years, show intense fluctuations in temperature every few thousand years. However, 42,000 years ago, most of these samples showed no transformation, except for some ice samples from the Pacific. But even if the change occurs primarily in the tropics, it should be visible in the ice, says Anders Svensson, a glacier researcher at the University of Copenhagen. “We just don’t see anything like that.”
The study authors go further, arguing that prehistoric climate change could explain the flood of strange events 42,000 years ago – such as the extinction of large mammals in Australia at the time. Neanderthals disappeared from the landscape in Europe, and complex cave paintings appeared in Europe and Asia. However, none of these milestones in human evolution matches well with magnetic flips 42,000 years ago, says archaeologist and radiocarbon expert Thomas Higham of the University of Oxford. The events did not happen suddenly, either. To link it to the field reflection “seems to me to stretch the evidence too far.”
The original of this article has been published in the scientific journal “Science” published by the American Society of Science. German version: cvei