lecture 2 Flashcards
earths formation
solar system coalesced from a rotating dust and gas cloud formed during a supernova
- accretion occured when particles accumulated into plantesimals. by attraction and then accumulated into proto-planets
- collisions generated intense heat
proto-earth formation
as temperature rose from impacts, proto-earth melted and differentiated
- molten iron pulled to the core
- silica rocky material floated upward to form
primordial
heat generated as the earth formed
- existing from the beginning of time
meteorites
fragemnts of proto-planets and planetesimals that record earths accretion
stony meteorites
made mostly from silica
- chondrites
- bumbly and have never been molten (before differentiation)
- oldest rocks in the solar system
achondrites
type of stony meteorite that lacks chondrules
- orriginate from differentiated mantle
stony-iron meteorites
silicates and nickel iron alloy
- boundary between outer silicate mantle and inner metalic core
iron meteorites
made of nickel-iron alloy
- originated in the core of planetesimals
4 types of meteorites
- chondrites
- achondrites
- stony-iron
- iron
william thompson
estimated age of earth by CONDUCTION
- calculated 100 million years
- assumed earth was rigid, homogenous
joohn perry
estimated age of earth by CONVECTION
- calculated 2-3 billion years
henri becquerel
calculated age of earth including RADIOACTIVITY
- an additional internal source of heat
- age can be measured by decay of radioactive elemets
naturally occuring radioctivity exposure
- soil and rock
- cosmic rays from space
- food drink and air
earths crust
outermost rocky layer
sedimentary rocks, granite and basalt
- average density of 5.5g/cm3
xenolith
foreign rocks brought up from mantle
earthquake seismic waves
reflected or refracted at major boundaries (core-mantle)
- p waves: faster and travel through liquid
- s waves: slower and cannot travel through liquid
rheology
describes how materials deform under stress
stress vs strain
stress = force/area strain = deformation that occurs due to stress
3 types of stress
- compression- perpendicular to surface (shortening)
- tension- perpendicular to surface (extension)
- shear stress- parallel to surface (distortion)
3 types of rheologies of solids
- elastic- deformation is recoverable
- brittle- may break at elastic limit
- plastic- deformation is permanent
ductile deformation
stress over long periods of time, plastic materials can flow
ex. brie cheese
factors of rheology
time, temperature and pressure
earths outer shell
liphosphere- solid, elastic
asthenosphere- soft plastic upper mantle
mesosphere- stiff plastic layer
oceanic vs continental crust
oceanic- basalt (higher density)
continental- granite
istostasy
equilibrium where lithosphere floats on denser, plastic asthenosphere
isostatic adjustment
addition or subtraction of mass from flaoting object leads to change in elevation
postglacial rebound
major glaciations at high latitudes
- surface is uplifted
what drives mantle convection
- heat from the core
- heated from below by primordial heat and from within by radioactivity
- internal heat energy is responsible for earthquakes, tsunamis, volcanoes and rise of mountains (landsliding)
sources of energy for natural hazards
- sun is nuclear fusion reactor: combining hydrogen to produce helium and releasing energy as heat and light
- uneven heating of oceans and atmosphere drives ocean currents
