They seem to base their estimates of the past solar cycle length on a study of only 79 years’ worth of data which is almost certainly too short for high accuracy, but the results are interesting nevertheless.
A pair of German researchers 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, reports Phys.org.
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.
Scientists know that the sun undergoes a sunspot cycle of approximately 11 years—some spots appear, grow cooler and then slowly move toward the equator and eventually disappear—the changes to the sun spots cause changes to the brightness level of the sun—as the level waxes and wanes, plants here on Earth respond, growing more or less in a given year—this can be seen in the width of tree rings.
In this new effort, the researchers gathered petrified tree samples from a region of Germany that was covered by lava during a volcanic eruption approximately 290 million years ago (during the Permian period), offering a historical record of sun activity.