1.a. variety of evidence for the theories of continental drift and plate tectonics

crust of earth

least dense material, thin outer layer, composded of tectonic plates, varies in thickness 6-70KM. 2 types: continental crust-thicker, lighter, lighter rock colour; oceanic crust- thinner, heavier, darker rock colour

separated from the mantle by the mohoroviviv discontinuity

mantle of earth

thickest layer, less dense rocks, silicate rocks, rich in iron and magnesium, approximately 2900km thick, upper mantle is rigid whilst most of the mantle is semi molten with temps near core reaching 5000^oc =convention currents generate

core of earth

denest material, iron and nickel, temps approx 5500^oc

lithosphere

formed from material that is solid and rigid, comprises the crust and top layer of the mantle.

asthenosphere- upper part of mantle- molten

material is relatively fluid, rock is soft and plastic and it flows in soft convection currents.

mesosphere- lower part of the mantle- solid

layer which is less fluid. stronger and more rigid than asthenosphere

outer core

liquid layer made of molten iron and nickel

inner core

solis layer made of iron and nickel

internal structure vs hazards

heat and pressure cause magma to move in convection currents, earths magnetism and magnetic fields of the earth, convection currents cause the plate to move which causes volcanoes and earthquakes

theory of continental drift

1911- German alfred wegener, found scientific paper that listed fossils of identical plants and animals found on opposite side of atlantic. looked for cases similar with organisms separated by oceans. orthodox science- such cases by postulating (claiming without proof) that land bridges once connected continents. close fit of africa and south america= not land bridges but continents once joined together. “a conviction of the fundamental soundness of the idea took root in my mind”

1912- theory that 300 mil year ago land on earth= single continent= pangaea- later split into 2 continents of laurasia- north and gondwanaland- south. today= further splitting. at time= ridiculted for idea- developed one of the most important geological theories

tectonic plates

7 major: north american, south american, african, eurasian, indo-australian, antarctic, pacific

minors too- one is nazca near south america

most likely cause of plate movement is the existence of convection cell currents in the asthenosphere, caused by heat from the core. this heat comes from a combination of radioactive decay in the core and residual primary heat. this heat causes the convection currents to rise, until they reach the lithosphere where they diverge. where the convection current descends due to cooling, the lithosphere is pulled downwards. plates are at their hottest nearest the mid oceanic ridges