(April 19, 2021)
The researchers examined the rings of the tree to look for changes in the amount of carbon-14 over a period of years, Gramling explains. Carbon-14 is useful not only for dating things, but because the interaction of cosmic rays with molecules in the atmosphere produces a lot of it. And when the Earth has a weakened magnetic field, more cosmic rays hit the planet.
The scientists indeed found a large spike in carbon-14 in the tree, which they could then compare with the rock record that indicated a magnetic reversal. (…)
In addition, there is the documented rise in cave art right about 41,000-42,000 years ago, Gramling points out.