A team from the University of New South Wales in Australia has discovered a very ancient and well-preserved log that they used to date the last reversal of the earth’s magnetic field very precisely to 42 ka (thousand years) ago. Using climate modelling and whatnot, they calculated a detailed timescale and deduced that the magnetic-field reversal – known as the Laschamps Excursion – coincided with high solar activity and may have caused glaciation in North America and a relatively sudden change in the climate in Australia, which may in turn have led to the extinction of the Neanderthals and some early modern human cultures, and of megafaunas in Australia.
Because the field reversal occurred 42 millennia ago, the team dubbed it the Adams Event, in honor of Douglas Adams, who wrote in Hitchhiker’s Guide to the Galaxy that the answer to life, the universe, and everything is 42.
Very briefly, the team used the trunk of an ancient kauri tree, which had been well preserved in a bog, carbon-dated each ring, and correlated the results with other, existing data. As described in a news article in Science, they applied a climate model and, very briefly, deduced that the excess high-energy radiation from the sun depleted the ozone layer and caused high-altitude cooling, which in turn altered the wind patterns and thus the climate near the surface. The change of climate caused the extinctions noted above. (You may find the technical article here. I read portions of it, but not surprisingly I found that it was not just Greek to me, but technical Greek to me.)
What caught my eye, however, was the claim that the field reversal somehow brought about the origin of cave paintings in Eurasia. In brief, the argument is that the high UV levels caused by the destruction of the ozone layer forced people into caves. Indeed, they argue that the handprints signal that the red ochre used for the paintings may also have been used as sunscreen. Well, IANAX[pert], but Wikipedia claims that a red hand stencil was made by a Neanderthal 64 ka ago. Their dates for modern humans are indeed in their range of 42 ka ago, or less. Still, it is hard to conceive that humans did not discover caves until they got severely sunburned, and I am at least partly sympathetic with those who told Science that the study may be too speculative.
Vivian Dullien directed my attention to the phys.org article. Nothing in this brief report is her fault.