Earth, Molnar 2015

Chapter 1

What is tectonics?

Study of large-scale processes that deform Earth’s crust.

Who proposed continental drift?

Alfred Wegener (1912).

What was Wegener’s supercontinent?

Gondwana (plus Pangaea concept later expanded).

Evidence for Gondwana?

Permian (~300 Ma) glacial deposits across southern continents.

What is continental drift?

Idea continents were once joined and drifted apart.

What is crust made of?

Al, Ca, Na, C-rich silicates (lighter elements).

What is mantle made of?

Denser Fe-Mg silicate minerals.

What is Moho?

Boundary between crust and mantle.

Why did Wegener use isostasy?

Archimedes principle explained crustal density differences.

Why was Wegener rejected?

Lacked mechanism for plate movement (1930s–40s).

What revived theory in 1950s?

Paleomagnetism + ocean floor mapping.

What is paleomagnetism?

Magnetic minerals align with Earth’s field when rock forms.

What key ocean feature was discovered?

Global mid-ocean ridge system.

Example of ridge system?

Mid-Atlantic Ridge + East Pacific Rise.

What is a mid-ocean ridge?

Underwater mountain chain with central rift valley.

What is a fault?

Fracture where movement occurs between rock blocks.

What is plate margin?

Boundary where two plates meet.

What are the 3 plate boundary types?

Divergent, convergent, conservative (transform).

What is divergent boundary?

Plates move apart, new crust forms.

What is convergent boundary?

Plates collide; subduction or mountain building occurs.

What is conservative boundary?

Plates slide past each other; no crust created/destroyed.

What is a normal fault?

Divergent boundary (tension).

What is a thrust fault?

Convergent boundary (compression).

What is a strike-slip fault?

Transform (lateral motion).

What is lithosphere?

Rigid crust + upper mantle plates.

What is asthenosphere?

Weak ductile layer plates move over.

What is key seismic evidence of structure?

Moho not sharp; velocity changes gradually.

What are plates driven by?

Mantle movement over asthenosphere.

What is global plate distribution? ~20 major plates covering Earth.

Largest plates?

Pacific, Africa, Eurasia.

Smaller plates examples?

Cocos, Caribbean, Juan de Fuca.

What is East Pacific Rise?

Gentler fast-spreading mid-ocean ridge in Pacific.

What happens at convergent ocean boundary?

Trench + volcanic island arc forms.

Examples of island arcs?

Aleutians, Lesser Antilles.

What is ridge axis?

Linear valley at center of mid-ocean ridge (20–40 km wide).

What is fracture zone?

Crack in crust; may become active fault if movement occurs.

What is difference fault vs margin?

Margin = boundary; fault = active movement zone.

Why ocean floor mapping important?

Showed continuous global ridge system post-WW2 surveys.