Tectonic plates

What are the main layers of the Earth?

Crust, mantle, outer core, inner core.

What is the lithosphere?

The rigid outer layer of the Earth including the crust and top part of the upper mantle.

What is the asthenosphere?

A plastic-like layer of the mantle that slowly moves and drags the lithospheric plates above it.

What did Alfred Wegener propose?

The theory of continental drift — that continents once formed a supercontinent (Pangaea) and drifted apart.

What evidence supported Wegener's theory?

Jigsaw fit of Africa and South America, matching fossils, rocks, and mountain ranges across continents.

What did sonar mapping of the ocean floor reveal?

Mid-ocean ridges, deep ocean trenches, and flat-topped seamounts.

Who proposed the idea of seafloor spreading?

Harry Hess.

What is seafloor spreading?

The process where new ocean crust is created at mid-ocean ridges, moves outward, and is destroyed at trenches.

What causes seafloor spreading?

Rising magma from mantle convection currents forms new crust as plates diverge.

What happens to old oceanic crust?

It is subducted back into the mantle at deep ocean trenches.

Who discovered paleomagnetism?

Vine and Matthews.

What did Vine and Matthews find?

Symmetrical magnetic stripes of normal and reversed polarity on either side of mid-ocean ridges.

What do magnetic stripes show?

That Earth's magnetic field has reversed many times and that new crust forms at ridges and spreads outward.

Who suggested mantle convection currents cause continental drift?

Arthur Holmes.

What are convection currents?

Circular movements of molten rock in the mantle caused by heat from the Earth's core.

What is basal drag?

Friction between moving mantle convection currents and the base of tectonic plates, dragging them along.

Where is basal drag strongest?

Near divergent boundaries where magma rises and new crust forms.

What is slab pull?

The gravitational force where a dense subducting plate sinks into the mantle, pulling the rest of the plate with it.

Why is slab pull important?

It is the most powerful driving force of plate movement, speeding up seafloor spreading.

What is the difference between basal drag and slab pull?

Basal drag pushes plates via mantle flow, while slab pull pulls plates down due to gravity at subduction zones.

What is a divergent (constructive) boundary?

Where two plates move apart and new crust forms as magma rises.

What landforms are created at divergent boundaries?

Mid-ocean ridges, rift valleys, volcanic islands, and shallow earthquakes.

Example of a divergent boundary?

Mid-Atlantic Ridge or East African Rift.

What is a convergent (destructive) boundary?

Where two plates move toward each other and one subducts beneath the other.

What landforms are created at convergent boundaries?

Ocean trenches, volcanic arcs, fold mountains, and subduction zones.

Examples of convergent boundaries?

Andes Mountains, Himalayas, Mariana Trench.

What is a collision boundary?

A type of convergent boundary where two continental plates collide and form mountains (no subduction).

Example of a collision boundary?

Indian Plate colliding with Eurasian Plate forming the Himalayas.

What is a transform (conservative) boundary?

Where two plates slide past each other horizontally without creating or destroying crust.

What landforms are created at transform boundaries?

Fault lines, offset streams, and earthquake zones.

Example of a transform boundary?

San Andreas Fault in California.

What is the Benioff Zone?

A sloping region of earthquake foci along a subducting plate marking where the descending plate bends, grinds, and fractures as it sinks.

What does the Benioff Zone prove?

It is direct evidence of subduction and plate movement.

What is a subduction zone?

The area where one tectonic plate is forced beneath another into the mantle.

How are earthquakes distributed at subduction zones?

Shallow near trenches and deeper inland along the Benioff Zone.

What are the main driving forces of plate movement?

Mantle convection, basal drag, and slab pull.

What land-based evidence supports plate tectonics?

Continental fit, matching fossils, rock types, and glacial striations across continents.

What ocean-based evidence supports plate tectonics?

Mid-ocean ridges, symmetrical magnetic striping, and increasing age of ocean floor away from ridges.

What is the key for divergent boundaries on maps?

Red line or arrows pointing away (⟶ ⟵).

What is the key for convergent boundaries on maps?

Blue line with triangles pointing toward subduction (▸▸▸).

What is the key for collision boundaries on maps?

Purple line with triangles on both sides (▸◂).

What is the key for transform boundaries on maps?

Green or black line with opposite arrows (⇆).

What is the key for subduction zones on maps?

Blue line with small triangles pointing toward the overriding plate (—▸▸▸).

What landforms occur at divergent boundaries?

New ocean floor, volcanic ridges, and rift valleys.

What landforms occur at convergent boundaries?

Deep ocean trenches, volcanic arcs, mountain ranges.

What landforms occur at transform boundaries?

Faults, linear valleys, and displacement of surface features.