Outline Alfred Wegener’s theory of continental drift.
- 1912 German meteorologist and geophysicist.
- claimed that the continents were once connected to each other and that they were once a large land mass called pangaea, so the continents must have somehow seperated and drifted across the oceans.
- this is what he called continental drift.
continental drift support: the shape of continents.
- the continents seemed to fit like a jigsaw, especially South america and Africa.
continental drift support: fossil evidence.
- same fossils of prehistoric species were found on continents far apart.
- so he thought that the continents shifted, taking the fossils with the,.
- he rearranged the continents so the distribution of the mossils matched up across the continents.
Outline Hess’s theory of sea floor spreading
- 1962 American geologist Harry hess.
- used sonar to map the bottom of the pacific ocean
- he saw underwater mountains
- he propsed: new crust was being formed at the ocean ridges and spreading outwards- seafloor spreading.
- the crist was sinking down into the earth to form ocean trenches- subduction
Proving seafloor spreading. - magnetic stripping.
- when molten rock solidifies magnetites line up with the magnetic field of the earth.
- the earths magnetic field changes and is preserved in the rock as it forms
- patterns and strips of rock with alternating magnetism are symmetrical on either side of the mid-ocean ridge.
- supports new seafloor being added equally on either side of the ridge.
Proving seafloor spreading- age of the sea floor.
- the further the rocks of the sea floor are from the are from the mid ocean ridges, the older they are
so: new rock forming near the ridges move outward away from the ridge.
Proving seafloor spreading- sediment thickness.
- sedimentary rocks are thicker therefore sediments falling for longer on the rocks on the sea floor, further away from the ridges.
use a model to demonstrate sea floor spreading.
(look at the book)
1) at the mid-ocean, tectonic plates diverge.
2) Magma rises from the asthenosphere to fill the gaps creating anew oceanic crust.
3) As new crust forms old crust is pushed away from the edge.
4) the lithosphere moves on top of the flowing asthenosphere, causing the plates to spread apart.
Theory of plate tectonics.
- explains how the earths outer shell (lithosphere) is divided into several large, rigid plates that flow on the semi-fluid asthenosphere beneath.
- tectonic plates move and interact at their boundaries to cause geological activites.
Theory of plate tectonics, recent evidence, Gps
- GPS Global Positioning system
- meausres the precise movement of tectonic plates and how fast they are moving,
theory of plate tectonics, recent evidence, eathquake positioning
Earthquake positioning
- earthquakes occring at the boundaries of plates supporting that tectonic plates are responsible for them
theory of plate tectonics recent evidence radiometric dating.
radiometric dating
- shows that the youngst oceanic rocks are at mid-ocean ridges indicating that new crust is formed and supporting the seafloor spreading
- dating rocks in subduction zones confirms that older oceanic crust is recycles back into the amnte.
- rocks in mountain ranges reveal where the tectonic plates have collided
- volcanic activity reveals connection between tectonic activity and volcanic erruption.
mechanics of movement- convection currents
convection currents
- theory on how plates move on the asthenosphere
- plates are dragged along as hot magma in the asthenosphere rises up and flows under the plates = convectional currents
- as the liquid rock flows friction between it and the tectonic plate causes movement.
mechanics of movement- gravity. (slab pulling)
- plates of subductions zones(region where one tectonic plate is forced bentath another)are denser than the ones at the mid ocean ridges.
theory: gravity pulls the heavy and denser plate donwards into the subduction zone and pulls the plate into the trench and away from the ocean ridges. - so the plates are pulled apart.
mechanics of movement- gay. (ridge push)
- new oceanic crust forming at the ridgs aboce the rest of the crust.
- gravity pulls the new crust downwards.
- this would push on the older crust below and to its side, so the plates move sideways.
mechanics of movement- rifting and continental drift.
Proposed: rifting occurs hen the earths crust cracks and subsides, allowing water to fill the gap.
- new crust forms at the mid ocean ridge and pushes the continents and ocean floor.
- explaines wegners idea of drifting continents.
explain the importance of convetion currents in the movement of earths tectonic plates.
- transfer heat from the earths interior, cuasing hot magma to rise, pushes plates apart at mid ocean ridges, cooler slabs sink into the subduction zones, pulling plates together.
- generates force that drives plates and geological activities
- contributes to recucling oceanic and continental crust=seafloor spreading and subduction.
type of interactions and examples, diverging boundaries.
-tectonic plates move apart in opposite directions
- leaves a rift(a deep crack)
- magma from the asthenosphere rises up into the rift and solidifies as it cools: new crust is formed
CONSTRUCTIVE.
e.g. Mid-atlantic ridge running through iceland
- the island is widening as new crust forms
- 2-5 cm per year, bc constant volcanic eruptions cause magma to spew into the rift.
type of interactions and examples, converging boundaries.
- two plates collide head on wit each other
- rock is destroyed: DESTRUCTIVE
- forms mountains, island chaines, underwater trenches which depends on what types of crust collide.
Converging boundaries: mountains, volcanoes and trenches.
- oceanic crust colliding with continental crust result in the denser oceanic plate subduct.
- subduction of denser continental plate= fold mountains and volcanoes.
- deep ocean trenches form at the subduction zone.
e.g. Nazca plate colliding with the South American plante = the andes mountains and peru chille trench
- subducting plate sinks into the how mantle, heat from friction, melting point, forming magma and destruction of oceanic crust.
Converging boundaries: island arcs
- oceanic plates collide, faster moving plate subducts, forming deep tranches.
- descending plate melts into magma
- magma rises to the surgace to creat a chain of volcanic islands.
e.g. mariana trench and island arc
- Pacific ocena ollided with the Mariana plate
- result a string of volcanic islands form an island along the boundaries of these plates.
Converging boundaries: high mountain systems.
- two continental plates collide and both are pushed up since neither is denser than the other
- the high mountain system is created
e.g. Himalayas:
Indian plate and the eurasian plate collision results in the Himalayas.
type of interactions and examples, transform boundaries.
- two tectonic plates slide parallel to each other in opposite directions
- move slowly but can suddenly flip and turn into earthquakes
- Boundaries often have fold mountains and fault lines(cracks in the rock)
- fault cracks= numerous parallel lines.
e.g. San Andreas Fault:
= Pacific plate and the NA plate fault
- near Los angelos and san fransisco
- significant movement and massive earthquakes.
