(Phys.org)—A pair of researchers affiliated with the Natural History Museum in Chemnitz and Technische Universität Bergakademie Freiberg, both in Germany, has found evidence in ancient tree rings of a solar sunspot cycle millions of years ago similar to the one observed in more modern times. In their paper published in the journal Geology, Ludwig Luthardt and Ronny Rößler describe how they gathered an assortment of petrified tree samples from a region in Germany and used them to count sunspot cycles.