1.2 Plate tectonic theory Flashcards
What is plate tectonic theory
A set of concepts to try and explain the formation and distribution of the earths structural features by the movement of plates
Who created the earliest plate tectonic theory and what was it
In 1912, Alfred Wegener suggested that 300 million years ago, there was a single continent called Pangea which then split off slowly into the continents we know today, but due having little evidence he was dismissed
What is some geological evidence to support plate movement
Jigsaw contents on map
Rock sequences matching up in countries opposite ends (Scotland and Canada)
Glacial deposits in hot regions like India
What is some biological evidence to support plate movement
Fossils (rock, animal, plat) such as the Mesosaurus being found in South America and Africa.
What is the most prominent EVIDENCE in support that plate movement happens
Sea floor spreading at the Mid-Atlantic ridge , founded in 1940
What is sea floor spreading and how do we know it exists
When new oceanic crust is formed through volcanic activity, causing the plates to move apart.
We know it exists because of the alternating polarity of rocks
How does the alternating polarity of rocks prove sea floor is spreading
IRON PARTICLES erupted in lava, ALIGN with the earths MAGNETIC FIELD and solidify. Due to the earths alternating polarity, rocks become ALTERNATELY ALIGNED in a series of STRIPES, pointing to either the north or South Pole.
This pattern suggests crust is slowly spreading away from the boundary, as new patterns appear
What are the 2 different kinds of polarity and how often does it change
Every 400,000 years
Normal - north pole
Reversed - South Pole
What are the 3 reasons sea floor spreading happens
Gravitational sliding (hotspots)
Ridge push
Slab pull
How are convection currents made
Hotspots are created when certain parts of the mantle are heated more than others.
Hotspots heat the lower mantle, causing currents to rise and spread into the asthenosphere before cooling and sinking, creating a current
How does gravitational sliding happen at ocean ridges
As the lithosphere moves away from an ocean ridge it cools and thickens, deepening and sloping the boundary between the lithosphere and asthenosphere
Gravity pushes the lithosphere infront of itself (ridge push)
Gravity causes the plate to be subjected by its own weight and pulls the rest of the plate down (slab pull)
What are the 2 different kinds of plates
Contiental
Oceanic
What are the characteristics of a continental plate
30-70km Thick
Old
Light density
Made of granite and aluminium
What are the characteristics of an oceanic plate
6-10km Thick
New
Heavy density
Made os basalt and magnesium
How was the earth divided up before plate tectonic theory
1.2. The Inner and Outer core (Solid dense iron rock, 5000C hot from primedorial heat)
- The mantle ((Semi-)Molten rocks in a viscous form, 1000-3000C hot)
- The crust (solid top layer of earth made of elements such as oxygen, carbon and aluminium up to 70km thick)
