EQ 1: what is the evidence for continental drift and plate tectonics?

what is the structure of the earth?

crust (lithosphere, asthenosphere, moho) mantle, outer core, inner core

what is the lithosphere?

the rigid, brittle outer part of the earth, consisting of the crust and upper mantle, broken up into tectonic plates

what is the asthenosphere?

the layer of the upper part of the mantle, below the lithosphere
rocks are ductile and flow and deform plastically

what is the moho?

the boundary surface between the earth’s crust and mantle
depth of 10-12km under ocean bed and 40-50km under continents

what is the surface temperature of the crust?

400 degrees celsius

what is the physical state of the crust?

solid

how do seismic waves behave in the crust?

surface and body waves able to pass through

what are the two parts of the crust?

oceanic and continental

what are features of the oceanic crust?

denser (3.0g/cm3), 5-10km thick, very young (under 200m years), made of basalt, silicone and magnesium (sima)

what are feaures of the continental crust?

less dense (2.7g/cm3), mean thickness of 35km, older (over 1500m years), made of granite, silicone and aluminium (sial)

what are features of the mantle?

temperature of 870 degrees celsius, less dense to medium density (3.3-5.4g/cm3), upper made of olivine lower made of magnesium silicate, phases of liquid and solid in layers, body waves pass through at variable rates due to density changes

what are features of the outer core?

temperature of 4400-6100 degrees celsius, dense (9.9-12.3g.cm3), made of 12% sulphur and 88% iron, liquid and generates a magnetic field, only P waves able to pass through & S-wave shadow zone formed from 105 degrees from focal point

what are features of the inner core?

temperature of 7000 degrees celsius (radioactive decay), very dense (13.5g/cm3), made of 20% nickel and 80% iron), solid and radiates heat, only P waves reach and pass through but refraction at core-mantle boundary forms a shadow zone between 105 and 140 degrees from focal point

what is continental drift?

the theory that the continental landmasses have changed position over time, formed by Alfred Wegener

what are convection currents caused by?

the heat produced from radioactive decay in the core
linked to movement of plates leading to creation of new oceanic crust or destruction of existing crust

what are more recent theories of plate movement?

gravitational forces (ridge push and slab pull)

what is the process of ridge push?

as magma rises, it cools and solidifies to form new crust
this creates a mid-ocean ridge
force of gravity pushes newly formed crust outward and away from ridge

what is the process of slab pull?

cold, older and denser plate material sinks into the mantle at deep ocean trenches and pulling the rest of the plate with them as gravity causes them to slide downwards

what are three pieces of evidence from wegener for continental drift?

continent jigsaw + geological, fossil evidence, and glacial evidence

why does the continent jigsaw + geological evidence provide evidence for continental drift?

the bulge of africa fits the shape of the coast of n. america
brazil fits along the coast of africa beneath the bulge, broad belts of rock in africa and s. america are the same type and match when the continents are joined

how does fossil evidence provide evidence for continental drift?

the fossil remains of the mesosaurus are exclusively found in s. africa and se america

how does glacial evidence provide evidence for continental drift?

glacial striations on rocks showed that glaciers moved from africa → atlantic ocean → south america
this glaciations is most likely if atlantic ocean was missing and continents joined

what is a piece of evidence that supports sea floor spreading?

paleomagnetism

what is paleomagnetism?

the permanent magnetisation locked into rocks when they form which is used to reconstruct past plate movements and plate tectonic theory

how does paleomagnetism provide evidence for sea floor spreading?

the magnetite in basalt align with the earth’s magnetic field
earth magnetic field switches over time → symmetrical patterns of normal and reversed magnetic rock

what are the three types of plate boundaries?

divergent, convergent, transform

what happens at divergent plate boundaries?

1) semi-molten mantle is heated and rises towards the surface, escaping to ocean floor to form underwater volcanoes and new oceanic lithosphere
2) as mantle rises towards the surface below the ocean ridge, decompression occurs and hot rock starts to partially melt
3) this produces basaltic volcanoes with pillow lava in underwater eruptions

what is an ocean ridge?

longest continuous uplifted features on surface of planet, forming a linear patterns and normally through the middle of oceans

what is an example of an ocean ridge?

the mid-atlantic ridge

what caused the formation of the mid-atlantic ridge?

the divergence of the eurasian and n. america plates in the mid-atlantic, running through iceland and extending for ~16000km

what are features of volcanic activity located on the mid-atlantic ridge?

series of underwater volcanoes, can appear above sea level e.g. Iceland (200m above sea level)
1/3 of iceland’s lava flows are <1000 years old, the country is not older than 16m years
1/3 of lava emitted on earh’s surface in last 500 years found in iceland

what are the three types of convergent plate boundaries?

oceanic-continental, oceanic-oceanic, continental-continental

what is the process of oceanic-continental convergent plate boundaries?

1) denser oceanic plate is forced under continental and subduction occurs due to ridge push and slab pull
2) ocean trench caused by downwarping of oceanic plate which descends at a 30-70 degree angle, causing intense heat and friction. releases large amounts of energy in deep focus earthquakes
3) buckling of plates causes sediment to uplift → mountain chains and composite volcanoes

what is an example of an oceanic-continental convergent plate boundary?

the andes - nazca plate moves eastwards towards american plate at ~79mm per year
nazca plate forced under s. american, marked by alacama trench
earthquakes at benioff zone

what is the process of oceanic-oceanic convergent plate boundaries?

1) same principle of subduction
2) slightly denser of the two oceanic is subducted due to slab pull and ridge push
3) creates trench and earthquakes due to tension
4) descending plate melts due to friction, less dense magma rises creating island arcs

what is an example of an oceanic-oceanic convergent plate boundary?

the caribbean islands - s. american plate subducts under caribbean plate
earthquakes at benioff zone
subduction of s. american plate causes sea water to go deep into mantle, lowering MP of mantle and causing partial melting → magma can be erupted as andesite e.g. montserrat 1990s

what is the process of continental-continental convergent plate boundaries?

1) little subduction as continental plates are much less dense → no volcanic activity
2) faulting and uplift due to ridge push → shallow focus earthquakes
3) causes synforms (upturned folds) and antiforms (downturned folds)

what is an example of a continental-continental plate boundary?

the himalayas - collision between indian plate and eurasian plate
himalayas are still rising 1cm+ per year as india continued to move northwards into asia

what is the process of transform plate boundaries?

1) two plates move laterally past each other
2) shallow focus earthquakes occur, with occasional major events happening after build-up of pressure
3) sometimes visible tearing of earth is seen as drainage is modified as river courses are deflected

what is an example of a transform boundary?

san andreas fault, pacific plate moving northwest at ~6cm per year, n. american plate moving at ~1cm per year
california has 2/3 earthquakes each year (5.5+ on richter scale)

what is an example of a hotspot?

the hawaiian island chain