Episode Links:
The Drake Equation (http://www.seti.org/drakeequation)
Winston Churchill’s essay on alien life found (https://www.nature.com/news/winston-churchill-s-essay-on-alien-life-found-1.21467)
Zookeepers, Alien Visitors, Or Simple Life (https://www.seti.org/seti-institute/project/details/zookeepers-alien-visitors-or-simple-life)
Sir David Gill (http://adsabs.harvard.edu//full/seri/ApJ../0040//0000161.000.html)
Tsiolkovsky - Russian Cosmism and Extraterrestrial Intelligence (http://adsabs.harvard.edu/full/1995QJRAS..36..369L)
