Why should other lifeforms require similar conditions to those here on Earth?
Drake’s Equation starts with a premise that we expect that other lifeforms will require similar conditions to exist as we have here on Earth. This needs to be justified. This notion is based on two observations about life here. Firstly, light elements such as Hydrogen, Carbon, and Oxygen which make up a significant fraction of the mass of all lifeforms here on Earth are amongst the most common elements found in the Universe. They are made by nuclear fusion in stars and ejected into space in the cataclysmic explosions at the end of their lives. Secondly, the chemistry of Carbon, the basis of our life, is by far the most diverse of any chemical element, so allowing a vast range of organic compounds to exist. The same chemistry These two facts would imply that most, if not all, of other lifeforms would be based on a similar chemistry. This would then require the presence of liquid water as a medium in which life could evolve so we would need a location where the temperature lies between z
