Which of the following best describes why the Drake equation is useful in the study of astrobiology?
1. It helps us think about the factors that would determine the likelihood that we could discover other civilizations.
2. It tells us how many SETI telescopes will be necessary to ensure success in the search for extraterrestrial intelligence.
3. It gives us a way to estimate the number of planets on which life has at some time arisen.
4. It gives us a way to determine the precise number of civilizations that have ever existed in the Milky Way Galaxy.
