asthenosphere

lithosphere

mesosphere

Lithosphere (hard)

Asthenosphere (soft)

Mesosphere

Mantle- 1000oCmesosphere

•Solid•~ 2300 km thick

asthenosphere• Soft•~3000 km thick

lithosphere•hard •~100 km thick

Inner Core- 4300oC

• mostly iron core

• inner part is so compressed that it is solid

Outer Core- 3700oC

• iron and sulfur

• liquid Crust

• floats on top of lithospherecontinental crust (granite)

•20 to 70 km thick oceanic crust (basalt)

• ~ 8 km thick

Earth formed 4.6 bya

Principles of plate tectonics

• The Earth is composed of a mosaic of thin rigid plates (pieces of lithosphere) that move horizontally with respect to one another

• Plates interact with each other along their plate boundaries

• Plate boundaries associated with tectonic activity (mountain building, earthquakes, active volcanoes)

Alfred Wegener

• Proposed Theory of Continental Drift (1915)• Failed to provide a mechanism

Evidence for Continental Drift

• continental shape• similar geology • fossil evidence (animal and plant)• volcano and earthquake zone• paleomagnetism

Objections to the continental drift model

• Wegener envisioned continents plowing through ocean basins

• Wegener did not provide a plausible mechanism to explain how the continents could have drifted apart

• Most Earth scientists rejected continental drift because it was– Too far-fetched– Contrary to the laws of physics

Lacked technologyLacked technology

Evidence for continental drift

• Matching coastlines on different continents

Evidence for continental drift

• Matching mountain ranges across oceans

300 million years agoToday

Evidence for continental drift• Glacial ages and climate evidence

Mesosaurus

Distribution of fossils such as Mesosaurus

Present Day

Jurassic 135 mya Cretaceous 65 mya

Triassic 200 myaPermian 225 mya

Marie Tharp

Marie Tharp's "World Ocean Floor Map”

1977

Evidence for plate tectonics• Pattern of worldwide earthquakes (left)

matches plate boundaries (right)

Hess- Convection Cell TheoryHess- Convection Cell Theory

The 3 types of plate boundaries

1. Divergent

2. Convergent

3. Transform

Divergent plate boundaries

• The Mid-Atlantic Ridge is a divergent plate boundary where sea floor spreading occurs

Divergent plate boundaries

• Iceland sits atop a divergent plate boundary where continental rifting occurs

Divergent plate boundaries

• Formation of an ocean basin by rifting and sea floor spreading

Convergent plate boundaries

• Convergent plate boundaries vary depending on the type of crust

a. Ocean-continent

b. Ocean-ocean

c. Continent-continent

Convergent plate boundaries

• An ocean-continent convergent plate boundary produces the Cascadia subduction zone and Cascade Mountains

Convergent plate boundaries

• A continent-continent convergent plate boundary produces the Himalaya Mountains

Transform plate boundaries

• Transform plate boundaries occur between segments of the mid-ocean ridge

• Can also occur on land (ex: San Andreas Fault)

The world as it may look 50 million years in the future

Glomar Challenger (1960’s)Deep sea ocean drilling

S

N

Mid-Ocean Ridge (Atlantic Ocean)

There have been 170 reversal in the last 76 million years. The earth’s present orientation has existed for the past 60,000 years.

+ +++ + +--- - - -

Age of the Atlantic