Oceanography Chapter 6

6.1 Continental Drift Hypothesis

Who proposed the continental drift hypothesis?

Alfred Wegener, a German meteorologist and polar explorer, in 1915.

6.1 Continental Drift Hypothesis

What is the name of Wegener’s book?

The Origin of Continents and Oceans.

6.1 Continental Drift Hypothesis

What evidence did Wegener use to support continental drift?

Pangea [laurasia(north) Gonwanaland (south(]

Fossil Evidence

Glacial Deposits

Folded rock belts across oceans

6.1 Continental Drift Hypothesis

Panthalassa

Land surrounding Pangea

6.1 Continental Drift Hypothesis

Why was Wegener's idea not accepted initially?

He couldn’t explain the mechanism that caused continents to drift.

6.2 The Earth’s Layers

What are the three main compositional layers of the Earth?

• Crust (Oceanic: 4–7 km, basalt; Continental: 20–70 km, granite)

• Mantle (rich in Mg and Fe)

• Core (Iron and Nickel; outer core is molten, inner core is solid)

6.2 The Earth’s Layers

What are the Earth's layers based on physical properties?

• Lithosphere: Rigid crust + upper mantle (75–125 km thick)

• Asthenosphere: Hot, weak, plastic-like layer (extends to ~350 km depth, 1–2% molten)

6.3 Sea-Floor Spreading

How was seafloor spreading discovered?

• Echo sounding & magnetometer surveys in the 1950s

• Discovery of mid-ocean ridges (e.g., Mid-Atlantic Ridge)

• Thin sediment at ridges, thicker further away

• Magnetic polarity stripes on sea floor (normal/reversed)

6.3 Sea-Floor Spreading

What is paleomagnetism?

The study of changes in Earth’s magnetic field preserved in rocks; used to confirm sea-floor spreading.

6.3 Sea-Floor Spreading

Who explained the magnetic stripe pattern on the ocean floor?

Frederick Vine, Drummond Matthews, and Lawrence Morley.

6.4 Theory of Plate Tectonics

What is the lithosphere in plate tectonics?

A brittle shell (10–125 km thick) made of crust and upper mantle that moves over the asthenosphere.

6.4 Theory of Plate Tectonics

What are the 3 main types of plate boundaries?

• Divergent: Plates move apart (e.g., Mid-Atlantic Ridge, Afar Rift)

• Convergent: Plates collide (e.g., Himalayas, Andes, island arcs)

• Transform: Plates slide past (e.g., San Andreas Fault)

6.5 Anatomy of a Tectonic Plate

What are the characteristics of a tectonic plate?

• Part of the lithosphere

• Can have oceanic and/or continental crust

• Moves slowly (1–16 cm/yr)

• Tectonically active margins

6.6 Why Plates Move

What drives plate motion?

• Convection cells in the mantle: hot rock rises at ridges, cools and sinks at subduction zones

• Gravity and cooling of lithosphere

• Mantle plumes & hot spots (e.g., Hawaiian Islands, Deccan Traps)

6.7 Supercontinents

What is a supercontinent?

A large landmass formed by the merging of smaller continents due to plate movement.

6.7 Supercontinents

Name three known supercontinents and when they existed.

• ~2–1.8 bya: First large continent formed

• ~1 bya: Another supercontinent formed and broke up

• ~300–235 mya-million years ago: Pangea

6.8 Isostasy

What is isostatic adjustment?

Vertical movement of the lithosphere due to changes in loading (e.g., melting glaciers causing uplift).

6.9 Effects of Plate Movements

What geological features are caused by plate tectonics?

• Volcanoes: At divergent and convergent boundaries

• Earthquakes: At all types of boundaries

• Mountain building: At convergent and rift zones

• Changing continents & oceans

6.9 Effects of Plate Movements

How do plate tectonics connect to the rock cycle?

Tectonic processes create new rocks (igneous), deform rocks (metamorphic), and expose rocks to erosion (sedimentary).

Pangea

Supercontinent proposed by Wegener

Lithosphere

Rigid outer shell of Earth (crust + upper mantle)

Asthenosphere

Plastic-like layer beneath lithosphere

Convection cells

Circulating mantle currents that move plates

Mid-ocean ridge

Undersea mountain range where new crust forms

Subduction zone

Area where oceanic crust sinks into the mantle

Transform fault

Plates slide horizontally past each other

Isostasy

Floating equilibrium of lithosphere on asthenosphere

Hot spot

Volcanic area above a mantle plume (e.g., Hawaii)

The outer about 125 kilometers of the earth including both the crust and upper mantle consists of

hard, strong, rock of the lithosphere

Magnetic Stripes on the seafloor are roughly —— the ridge axis along where they were created

parallel and symmetric about