The Drake equation is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in our galaxy. It considers various factors such as the rate of star formation, the fraction of stars with planets, the number of habitable planets per star, and so on.
However, you mentioned using the "rare earth equation," which I'm not familiar with. If you could provide more information about this equation or its specific parameters, I can try to assist you further.