Earth Structure and Plate Tectonics - Unit 3

Crust

- Thin outer skin of earth and consists mostly of silicates

- Sectioned into oceanic and continental varieties

- solid rock

Mantle

- Thick middle layer composed mostly of silicates

- solid rock

Core

- Thick center region made of iron-nickel alloy

- separated between soldi rock inner region and liquid outer region

lithosphere

- strong, rigid outer layer of earth

- consists of crust and upper layer of mantle

Asthenosphere

- weaker, "plastic" layer below lithosphere

- consists of mantle

- solid, but not as rigid as lithosphere

Continental Drift Theory

- Proposed by Alfred Wegener in 1915

- All of Earth's landmasses were once joined together in a supercontinent

- This supercontinent (Pangea) began breaking up about 200 Mya

What are the lines of evidence used to support the continental drift theory?

- continent shapes seemed to fit together

- fossils across continents linked species

- rock types on continents matched in composition

- remnants of ancient climates though glacial striations and coal deposits

• suggests continents shifted in latitiude

What was the scientific basis for many people initially rejecting the continental drift theory?

Nobody could identify a credible mechanism/reason for why continents drifted

Exploration of the oceans in the 1940s led to many new discoveries, name the ones mentioned

- Ocean floor ridges

- Earthquakes originate from great depths beneath ocean trenches

- Magnetic field polarity patterns on ocean floor

- Some parts of ocean floor have only thin sediment deposits, suggesting

Summarize the Plate Tectonics Theory

- Lithosphere is broken into 20 plates with irregular shapes and sizes

- Plates move independently and are in constant motion in respect to each other

- Movements and collisions of the plates account for the major geologic features on Earth

Divergent plate boundary

- when plates move apart

- most on the ocean floor and create ocean ridges

- some on continents and create continental rifts

Convergent plate boundary

- also known as subduction zones

- oceanic/ocean convergence results in one plate subducting under the other

• underwater volcanoes

- oceanic/continental convergcence leads to oceanic plate subducting under continental plate

• continental volcanoes

- continental/continental convergence does not subduct and instead crashes together

• mountain ranges

Transform plate boundaries

- Plates slide past each other

- Most are found on ocean floor but some cut though continents

• San Andreas fault

Mantle plume

a column of very hot rock rising up through the mantle

Hot spot

location of mantle plume

hot spot track

Chain of volcanic structures produced by hot spot

What are some lines of evidence that support the plate tectonics theory

- Thickness of ocean floor sediments

• sediment thickness increases as you get farther from crest of ocean ridge

- hot spot tracks show accumulation of volcanic activity, and as you move further away from hot spot, the rock ages

- paleomagnetism records left in rock sediment on ocean floor correlate to polarity flips throughout history

Where do most earthquakes and volcanoes occur?

around plate boundaries

What program is used now to measure plate movement?

Global positioning system (GPS)

What is the most likely driver of plate movement?

mantle convection

What are the leading models for mantle convection

- Whole-mantle convection model

- Layer cake convection model

•Two zones of convection