How the Earth works Lecture 3: Plate tectonics Flashcards
Who first theorised tectonic theory?
Alfred Wegener, German Meteorologist. (1880 - 1930 )
Who theorised sea floor spreading?
Go into detail about the theory
Sea floor spreading was theorised by Harry Hess
Hess suggested that oceanic crust was created at ocean ridges which’s movement was driven by convection currents in the mantle and was destroyed at ocean trenches(via subduction).
What are the various forms of evidence of tectonic theory?
-Glacial evidence (Glacial erosion present in various continents, many of which are not at the poles, which suggests movement)
-Palaeontological evidence (e.g. climactic and fossils in various places)
-Geological similarities and mountain belts that were once together.
How are magnetic needles affected by the magnetic field?
The lines of Earths magnetic field is curved.
Magnetic dip needles are parallel to magnetic field lines, in relation to where the magnetic dip needle is to the pole.
This concept can be used to prove plate tectonics as in magnetic rocks their positioning is affected by the location of magnetic pole and their position in relation. As a result some magnetic rocks may be configured in a way that is incorrect when taking into consideration their location in relation to the pole, which suggests that these rocks may been moved at some point - Tectonics?
Describe and explain the magnetic field of the Earth.
The Earths core is made up of semi molten Iron, which is magnetic. As a result there are magnetic field lines around the Earth, as well as two poles/ends like a magnet.
These poles have are not in a constant position, and are constantly travelling around due to convection movement in the core. The Northern pole is currently moving towards Siberia.
Additionally these poles will switch every so often
The magnetic north pole is not properly aligned with the Geographic north pole. The difference between these poles is called the declination.
Describe how paleomagnetism behaves in high and low temperature
In high temperature environments:
-No magnetism
|
-Thermal energy of atoms is high
-Magnetic dipoles are randomly orientated
In low temperature environments :Permanent magnetism
-Thermal energy of atoms slows
-Dipoles align with Earth’s gravitational field
-Magnetic dipoles become frozen in alignment with field
Paleomagnetism: Polarity flips?
Every so often in Earths history the magnetic poles will switch.
Evidence of this can be found in layered lava flows.
True or false: The Lithosphere is rigid and the Asthenosphere is plastic like and bendy.
True
Describe the Divergent plate boundary
Divergent boundary—tectonic plates move apart.
Lithosphere thickens away from the ridge axis
Often creates ocean ridges. (Seafloor spreading)
Describe the Convergent plate boundary
Convergent boundary—tectonic plates move together via SUBDUCTION ( One plate sinking underneath another into the mantle.
Often creating ocean trenches as well as Volcanic island arcs.
Describe the Transform plate boundary
Transform boundary—tectonic plates slide sideways.
