it, he concedes that the search for life elsewhere in the universe naturally begins with the search for water, because no life as we know it could survive without liquid water He then begins a fascinating thought experiment with a question: Why must life exist as we know it? He ponders what would happen if life didn't need water. His first logical choice for a different medium is liquid ammonia (NH3). Ammonia is an interesting choice because it is similar enough in size, shape, molecular weight, and polarity to water. Ammonia has the following phase diagram: 4.0 3.5 Solid Liquid Gas 3.0 2.5 2.0 1.5 1.0 0.5 P (atm 100 200 300 T(K) w 1st attempt See Periodic Table See Hint Based on the phase diagram, what prevents ammonia from being a good solvent for life on Earth at standard temperature and pressure (STP12 Ammonia is a at STP