Ancient Trees & Magnetic Field

Radiocarbon from a 42,000-year-old kauri tree in New Zealand helped unravel Earth’s last magnetic upheaval. JONATHAN PALMER

Science magazine is accessible for most lay readers, even if their articles occasionally include a word we have never heard of, such as paleomagnetist:

Ancient kauri trees capture last collapse of Earth’s magnetic field

Several years ago, workers breaking ground for a power plant in New Zealand unearthed a record of a lost time: a 60-ton trunk from a kauri tree, the largest tree species in New Zealand. The tree, which grew 42,000 years ago, was preserved in a bog and its rings spanned 1700 years, capturing a tumultuous time when the world was turned upside down—at least magnetically speaking.

Radiocarbon levels in this and several other pieces of wood chart a surge in radiation from space, as Earth’s protective magnetic field weakened and its poles flipped, a team of scientists reports today in Science. By modeling the effect of this radiation on the atmosphere, the team suggests Earth’s climate briefly shifted, perhaps contributing to the disappearance of large mammals in Australia and Neanderthals in Europe. “We’re only scratching the surface of what geomagnetic change has done,” says Alan Cooper, an ancient DNA researcher at the South Australian Museum and one of the lead authors of the study.

The study not only nails in fine detail the timing and magnitude of the magnetic swap, the most recent in Earth’s history, but is also among the first to make a credible, though speculative, case that these flips can affect the global climate, says Quentin Simon, a paleomagnetist at the European Center for Research and Teaching in Environmental Geoscience in Aix-en-Provence, France. But some paleoclimate scientists are skeptical of the team’s broader claims, saying other records show few traces of climate upheaval.

Earth’s magnetic field is created by the flow of molten iron in the outer core, which is prone to chaotic swings that not only weaken the field, but also cause the poles to wander and sometimes flip entirely. The magnetic orientations of minerals in rock record long-lasting reversals, but can’t capture the details of a flip lasting hundreds of years, like the one 42,000 years ago…

Read the whole article here.

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