Lesson 2 - Continental Drift and Plate Tectonics Flashcards
What is continental drift?
The movement of the Earth’s continents relative to each other
What is the thickness of the lithosphere on the continents?
Up to 250km thick
What is the thickness of the lithosphere beneath the oceans?
Just 100km thick
What type of rock largely makes up the lithosphere?
Peridotite
What is the thickness of the Earth’s crust?
Around 35km thick
What type of rock composes the continental crust?
Granitic rock
What is the thickness of the ocean crust?
Around 7-8km thick
What type of rock is the ocean crust made of?
Basaltic rock
What layer does the lithosphere float on?
Asthenosphere
What is the asthenosphere?
A viscous lower layer that forms the upper part of the mantle
What is the process called that describes the movement of lithospheric plates?
Plate tectonics
How many major lithospheric plates are there?
Seven major lithospheric plates
What are the three types of plate margins?
- Conservative
- Constructive
- Destructive
What happens at conservative margins?
Plates slide alongside one another
At which type of margin does mantle material rise to form new oceanic crust?
Constructive margins
What occurs at destructive margins?
Lithosphere descends into the mantle and is destroyed
What is the role of ocean trenches in plate tectonics?
They are sites where lithosphere is destroyed
List two mechanisms that drive tectonic plate movement.
- Volcanic activity
- Convection of hot magma
What is the significance of plate tectonics in geology?
It is responsible for the configurations of continents and the creation and destruction of ocean basins
What happens to the ocean floor when it meets the continent at destructive plate boundaries?
The ocean floor is subducted as it is denser and thinner than continental rock
What occurs when two continents meet at a subduction zone?
The continental crust is too buoyant to be subducted and buckles, forming mountain chains
What are ophiolites?
Thin slivers of ocean crust that remain after the ocean plate is completely subducted
What is the suture zone?
The area where two continents joined
What is an example of continent-continent collision?
The formation of the Himalayas
How long ago did India crash into Asia, leading to the formation of the Himalayas?
Around 30 million years ago
What do constructive plate boundaries create?
Ocean crust
What do cooling and sinking oceanic crust form?
Abyssal plains
How often has the direction of the Earth’s magnetic field flipped?
At intervals of a few hundred thousand to a few million years
What is the maximum age of ocean floor observed?
About 160 million years
What forms on the ocean floor when magma cools and moves away from the axial ridge?
Magnetic anomaly stripes
What do transform faults do?
Offset the line of the boundary between two plates
What occurs around transform faults?
A narrow zone of shallow earthquakes
What is the area beyond the transform fault on either side known as?
The fracture zone
