However in a letter to
Nature (
Periodic mass extinctions and the Sun's oscillation about the galactic plane) these astronomers note the periodicity to be 26 million years.
In another letter to
Nature (
The Sun's motion perpendicular to the galactic plane) we are told "For all the models we consider, the most recent passage of the Sun through the galactic plane occurred in the past 3 Myr provided only that the present position of the Sun is between 0 and 20 pc above the plane."
Please note that the full cycle is double whatever of the above figures we go with.
