HE - 1.What is the evidence for continental drift and plate tectonics Flashcards
(18 cards)
What is the theory of continental drift?
Proposed by Alfred Wegener, it suggests that continents once formed a single landmass (Pangaea) and have since drifted apart.
What is the theory of plate tectonics?
The lithosphere is broken into tectonic plates that move over the asthenosphere due to convection currents driven by heat from the Earth’s core.
What are the main layers of the Earth involved in plate tectonics?
Lithosphere: Rigid outer shell (crust + upper mantle), broken into tectonic plates
Asthenosphere: Semi-molten layer beneath the lithosphere; plates move over it
Core: Heat source driving convection currents
What is the role of convection currents in plate movement?
Heat from the core causes the mantle to move in slow convection currents, dragging plates with them.
What is slab pull?
Slab pull is the main driver of plate movement. As a denser oceanic plate is subducted, it sinks under its own weight into the mantle and pulls the rest of the plate behind it.
What is ridge push?
At mid-ocean ridges, newly formed crust is elevated. Gravity causes it to slide down, pushing the plate away from the ridge — this is called ridge push.
How do slab pull and ridge push relate to convection currents?
Convection currents create upwelling at mid-ocean ridges.
This allows ridge push to begin.
As oceanic plates cool and become denser, slab pull becomes the dominant force.
What is sea-floor spreading and how does it support plate tectonics?
At mid-ocean ridges, new crust forms as magma rises and cools. This pushes older crust away, proving plates are moving apart.
What is paleomagnetism and how does it support sea-floor spreading?
Iron minerals in cooling magma align with Earth’s magnetic field. Bands of reversed polarity on either side of ridges show symmetrical spreading over time.
What does the age of sea-floor rocks tell us about plate tectonics?
Rocks are youngest near ridges and get older further away, confirming continual crust creation and outward movement.
How do ancient glaciations support continental drift?
Glacial deposits and striations found in now-warm continents (e.g. South Africa, India) suggest they were once joined and located near the South Pole.
How do fossil records support continental drift?
Identical fossils (e.g. Mesosaurus) are found on separate continents (e.g. South America and Africa), indicating the continents were once connected.
What are the main types of plate boundaries?
Divergent (constructive)
Convergent (destructive/collision)
Conservative (transform)
What happens at divergent (constructive) plate boundaries?
Plates move apart. Magma rises to form:
Mid-ocean ridges (e.g. Mid-Atlantic Ridge)
Volcanoes and fissures
Shallow earthquakes
What happens at oceanic-continental convergent boundaries?
Dense oceanic crust is subducted beneath lighter continental crust, forming:
Deep ocean trenches (e.g. Peru-Chile trench)
Fold mountains (e.g. Andes)
Volcanic arcs and intermediate/deep earthquakes
What happens at oceanic-oceanic convergent boundaries?
One oceanic plate subducts under another, forming:
Island arcs (e.g. Japan, Aleutians)
Ocean trenches
Submarine volcanoes and strong earthquakes
What happens at continental-continental convergent boundaries?
Neither plate subducts; the collision causes:
Fold mountains (e.g. Himalayas)
Large, shallow earthquakes
No volcanic activity
What happens at conservative (transform) boundaries?
No crust created or destroyed
Shallow focus earthquakes (e.g. San Andreas Fault)
No volcanic activity
