ASTRO 106 Lecture Notes - Lecture 2: Big Bang, Exoplanet, Radiometric Dating
Document Summary
What is life: hard to define, some traits of life: Ability to evolve: but consider some marginal cases: What is life (traditionally-defined) made of: 96% of living mass is composed of the most abundant non-inert elements: oxygen, Lack of carbon in non-living things gives a hint that it might be key for life. Can bond with itself and other elements (o, n, and h) Silicon is the 2nd most abundant element on earth, but it has weaker bonds and it is rarely found in earth life. Is water necessary for life: maybe not, but almost surely a liquid of some kind is needed to facilitate chemical reactions, water is a great liquid. Stays liquid at higher temperatures (good for fast chemistry) Polar molecule gives it useful chemical properties. Does life need water: other possible liquids: ammonia, methane, ethane might exist in liquid form on exoplanets, possible environments in our solar system include titan, which has lakes of liquid hydrocarbons.
