Plate Tectonics Flashcards
Explain Expanding earth theory
The earth was once covered in land and has expanded due to meteorites hitting the earth due to earths gravitational pull. The earth has now expanded so the continents have split from each other. This explains why fossils are common in different continents.
Explain Floating continent theory
The continents float on water or liquid mantle and sometimes sink and rise. This explains why marine fossils are sometimes found on land.
What is continental drift?
In 1912 Alfred Wegener proposed that the continents were not stationary but were drifting and once formed a supercontinent called Pangaea this was based on a few key observations: The close geographical fit of South America and Africa he described it like torn newspaper narrow Mountain belts restricted to Continental margins distribution of fossils such as mesosaurusand Lystrosaurus. He was criticised for making bold statements without solid evidence to back it up it wasn’t until 50 years later when evidence became available that his theory was accepted.
What is the mid ocean Ridge?
Harry has to Starbard that the sea floor was not flat as previously thought but actually had trenches and mountains he discovered that there was a submerged mountain range running down the centre of the Atlantic Ocean and named this the mid ocean Ridge.
Why is rock younger closer to the mid Atlanic ridge?
Magma rises from the mid ocean ridge creating new ocean floor while older ocean floor is pushed back into the magma. This is supported by magnetic striping.
What is magnetic striping?
The magnetic polarity of the earth reverses every 200,000 years. The iron in the ocean floor was examined to see where magnetic North was when it was formed and cooled this led to this discovery of magnetic striping.
Explain the contacting earth theory
As the coreof the earth cools it contacts and the rest of the world contracts with it. The continents crash into each other forming mountains e.g. Indian continent crashing into the Asian continent forming the Himalayas
What fossils prove the theory of continental drift?
Mesosaurus, Cynogoathus, glossopteris and Lystrosaurus
How many plates make up the earth
About 10 large plates and 20 small plates
Resite the layers of the earth from outer to inner
Crust, upper mantle, lower mantle, outer core, inner core
Name the 5 spheres
Atmosphere, hydrosphere, biosphere, lithosphere, asthenosphere
Define lithosphere
The solid consisting of the cross and parts of the upper mantle
Define asthenosphere
Layer below the lithosphere, it is plastic meaning it is a weak solid with some properties of a liquid
What are divergent boundaries?
Divergent boundaries are found where to plates are moving apart. This results in a crack known as a Rift Valley. Volcanic eruptions then create new crust.
What are Convergent boundaries?
Convergent boundaries form when two plates move towards each other. This is a destructive boundary.
What happens when an oceanic and continental plate collide?
The heavier oceanic plate is subducted under the continental plate. The ocaenic plate is then absorbed int the mantle.
What happens when to oceanic plates collide
Subduction occurs. The more dense plate is pushed under the other and is absorbed into the mantle.
Explain transform boundaries
Transform boundaries occur when two plates slide along each other. The scraping can cause earthquakes. This is a conservative boundary
What is a fold?
In result of commpression of strata, it bends and buckles creating folds
What is a fault?
If strata breaks along a line it is called a fault
Tension creates normal faults
Compression creates reverse faults
What is horst?
Multiple reverse faults
What is garben?
Multiple normal faults
What are stike slip faults caused by?
Shearing forces
Where are volcanic fissures found?
Divergent Boundaries
What causes Volcanoes in the middle of plates?
Hot spots in the mantle
What causes island chains
Volcanic hot spots
What determines volcano shape
The lava. Sticky slow flowing lava creates tall thin volcanoes. Thin fast flowing lava creates flat volcanoes
What causes earthquakes?
Movement of tectonic plates
What measure seismic waves
Seismometers that produce seismographs
Body waves travel where?
Through the earth
What are the two body wave
Primary which are fast and longitudinal and secondary which are slower and transverse
What does transerve mean
The wave moves perpendicular to the propagation
What does longitudinal mean
Waves travel in the direction of propagation
What two surface waves are there
Love, which move side to side like a snake and travel quickly and Rayliegh which are rolling waves and are very destructive
What are aftershocks
Minor temors that can be felt days after the earthquake
