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
Examples of biosignatures
Complex molecules like chlorophyll, phospholipids, some proteins; macromolecules bigger than 200 daltons, preference for chirality, biogenic eat
Red edge effect
Spectral signature of oxygenic photosynthesizing organisms
Defn of geosignatures
Evidence of life in the geology of an enviroment
Geosignatures of life on Earth
High levels of oxygen, methane, and hydrogen in an atmosphere that is out of equilibrium
Defn of geoindicators
Indications that life could be possible
Examples of geoindicators
Compounds produced in the presence of water, presence of an atmosphere, thermal gradients, chemical disequilibrium, internal differentiation, nutrient recycling, energy sources, liquid medium
Signatures of intelligent life
Structures, signals
Problem: evidence of a civilization may become less apparent as they develop
SETI’s mission
Search for ExtraTerrestrial Intelligence by looking for moderately random radio signals
very regular is pulsar, very random is background radiation
People: Dr. Benison
Lady that is friends with Dr. Mormile, guest lecturer
People: Witman
The potential biomass of the subsurface may be greater than the biomass of the surface
People: T. Onstott
Found life in South African mines that were adapted to the high heat, pressure, and salt concentrations like microscopic roundworms and fungi
People: Dr. Deamer
Phospholipids as biosignatures
People: Percival Lowell
Claimed canals on Mars were a sign of life
