Exam 2 Flashcards
General features of carbon that make it a good building block for life
small, can form four bonds, chiral, gaseous waste products, abundant, found in asteroids/meteorites, can be used in polar solvent
Bond strength in carbon compounds
CC bond is highest energy of all non-metal elements, bond strength between CC and CN are similar
Most reduced and oxidized form of carbon
Most reduced is methane (CH4), most oxidized is carbon dioxide (CO2)
Most reduced and oxidized form of silicon
Most reduced is silane (SiH4), most oxidized is silicate (SiO4)
Major disadvantages of silicon
Cannot form multiple (pi) bonds, silicates are very unreactive and silane is very unstable, needs non-polar solvent
Silicon’s use in life
Plant cell walls and diatom shells, mix of silicon and carbon may be used on planets with low carbon levels
Need for a liquid solvent
Mobility, dissolves some compounds and allows them to react while stabilizing others, temperature buffer
Advantages of a water solvent
Dissolve salts and hydrophilic molcules, strong dipole moment and hydrogen bonds, high specific heat, high enthalpy of evaporation, high surface tension?
Advantages of ammonia solvent
Common with some carbon-like properties, has a dipole moment and hydrogen bonding
Characteristic of life in a methane solvent
Reversed cell membranes
Advantages of subsurface life
Protection from temperature swings, no need for an atmosphere, solvents and energy sources may be present, increase in pressure and temperature with depth maintains liquid water
Metabolism and energy sources of subsurface life
Auto-chemotrophs use energy in inorganic chemical compounds, radioactive material to provide heat
Evolution in the subsurface
Stable environment leads to stabilizing selection and low diversity
Atmosphere-related risks to life
Cosmic and UV radiation, temperature swings, extreme weather, meteorite impacts
Characteristics of a planetary atmosphere that would be capable of supporting floating life
Dense, stable temperatures, liquid solvent, some surfaces, source of energy
Characteristics of life capable of surviving in a planetary atmosphere
Protection from radiation and free radicals, small, density of surroundings, possibly inclusions of oil or gas or special appendages
Characteristics of life in space
Low temperature, no pressure, cosmic/UV radiation, greatly reduced rates of metabolism, desiccation or formation of protective envelope layers
How habitable zones are detemined
Type and distance of star
Ranking of stars by heat (3)
A (hottest) -> G -> M (cooler, more common, our star)
Current number of exoplanets
3925+
Length of the stable period of a star of a certain size
Small stars are more abundant and last longer
Galaxy-level habitability
Presence of rocky planets, heavy elements like carbon/nitrogen/oxygen/metals, few supernovae, low radiation, moderate gravity, suitable host stars
Anthropic Principle
Our universe is unique and created the conditions that allow for life to occur and evolve
Defn of biosignatures
Indications of life, signatures that were produced by a living organisms or living organisms themselves
