D - Plate Movement Flashcards
What does the theory of plate tectonics state about Earth’s layers?
That Earth is composed of multiple layers, including a thin, rigid crust (both continental and oceanic) overlying the mantle and core.
How do images of Earth’s cross-section (like the first diagram) illustrate the planet’s structure?
They show layers such as the crust (0–3 miles thick for oceanic; up to ~40 miles for continental), the lithosphere (30–125 miles thick), the asthenosphere (50–200 km depth), upper and lower mantle, and the outer and inner cores.
What are the two main sources of Earth’s internal heat?
Radiogenic heat (from radioactive decay in the mantle and crust) and primordial heat (left over from Earth’s formation).
According to the diagrams, which heat transfer mechanisms occur within Earth?
Convection (in the mantle), conduction (through solid layers), and advection (movement of heat via fluids or molten rock).
What is meant by ‘global internal heat flow’?
It refers to the large-scale transfer of heat from Earth’s interior to its surface, primarily via convection currents in the mantle.
Define subduction in plate tectonics.
Subduction is when one lithospheric plate (usually oceanic) plunges beneath another plate at convergent boundaries.
Where do subduction zones commonly form?
They form where an oceanic plate collides with another plate (oceanic or continental), causing the denser plate to sink below the other.
What is rifting, and where does it occur?
Rifting is the process where tectonic plates move apart at constructive plate boundaries (e.g., East African Rift Valley, Thingvellir in Iceland).
How do the diagrams illustrate the process of rifting?
They show upwelling convection in the mantle, tension faulting in the crust, magma intrusion along faults, and repeated widening as hot material wells up beneath the spreading plates.
Why is hot material associated with rift valleys less dense than older plate material?
Because it is hotter and more buoyant, causing it to rise and fill the gap created by diverging plates.
Give an example of a rift valley and the suspected cause behind it.
The East Africa Rift Valley, believed to be caused by hotspot activity and mantle upwelling beneath the continent.
What are the thickness differences between oceanic and continental crust?
Oceanic crust is thinner (around 3–5 miles / 5–8 km) while continental crust is thicker (up to about 12–40 miles / 20–60 km).
What role do convection currents play in plate movement?
They drive the motion of tectonic plates by circulating heat within the mantle, pushing and pulling plates at boundaries.
How do the images show that plate motion can create mid-ocean ridges?
They depict mantle convection causing partial melt under oceanic crust, leading to upwelling magma and ridge formation at divergent boundaries.
What is the significance of the lithosphere and asthenosphere in plate tectonics?
The lithosphere (rigid crust + upper mantle) forms tectonic plates, while the softer asthenosphere beneath allows these plates to move.
