tectonic plates

why is earth hot on the inside? (2 reasons)

1) residual heat from gravitational construction and asteroid impacts

2) active source: radioactive decay of unstable isotopes

lithosphere

upper rigid parts of earth’s crust. includes tectonic plates

astenosphere

below the lithosphere. plastic, partly molten rock that allows plates to drift around

convection (earth’s internal heat)

• cycles hot and cold currents.

in mantle→ plate tectonics→ topography

in liquid outer core→ earth’s magnetic field

alfred wegener (proposal, year)

german meteorologist who proposed continental drift in 1912. coined “pangea” supercontinent. was not taken seriously

evidence for continental drift hypothesis (5 total)

1) fit of continents

2) distribution of earthquakes and volcanoes lines up with topography

3) identical fossils on far away continents (not flying ones)

4) matching mountain belts of the same exact age on separate continents

5) latitude rock evidence: past glaciers leave striations on rocks. certain rock types only form at specific latitudes (eg limestone from corals)

evidence for sea floor spreading (2)

1) mid ocean ridges discovered in WWII

2) anomalies in magnetite stripes in the rocks→ show us the sea floor was made over time

why did science accept the sea floor spreading hypothesis (1960) but not the theory of continental drift (1912)

wegener did not provide a reason why plates could move and later they found the mechanism

mid ocean ridges

long, continuous, massive mountain ranges. where new crust forms.

tuzo wilson

coined the terms “plate tectonics” and “transform faults”

characteristics of divergent boundaries

high heat flow from magma rising. formation of new crust. MORs.

characteristics of convergent plate boundaries

• subduction zone

• deep sea trench

• volcanic arc

• mountain ranges

why does one plate subduct under the other?

more dense→ oceanic (magic) under continental (felsic)

transform boundary characteristics

• shallow earthquakes varying in size

• vertical fractures

• very little volcanic activity

oceanic plates are primarily (mafic or felsic)

mafic

continental plates are primarily (mafic or felsic)

felsic

what are the 4 tectonic plates nearest to us (in order)

north american plate (where we are), juan de fuca (subducting under us), explorer plate (north of juan de fuca and pacific plate (diverging from juan de fuca)

earth’s magnetic field is generated by:

convection in the earth’s outer core

how are rocks magnetized?

as molten lava cools magnetite minerals in cooling lava line up to current magnetic field lines. magnetic “record” becomes frozen in rock

earth’s magnetic field is ___ near poles and ___ near equator (horizontal/vertical)

vertical, horizontal

what magnetic stripes in rocks reveal

a history of magnetic field reversals and if the continent has moved in latitude

tectonic plates

upper, rigid parts of earth’s lithosphere. drifting around on molten asthenosphere.

volcanic arc

arc shaped chain of continental islands (ocean) or continental volcanoes. occur at subduction zones

hotspots/mantle plumes (example)

remain stationary as plates drift on top of them. leave a little track of volcanic islands showing us how the plate has moved (eg hawaii)

how fast do tectonic plates move?

varies. ~1-15 cm per year.

3 reasons plates move

1) convection →mantle drag

2) slab pull→gravity/physical properties of plates

3) ridge push→ mid ocean ridges