the Dynamic Earth and Plate Tectonics

Early Ideas on a moving Earth• Alfred Wegener proposed idea: “Continental

Drift”– Stated that all continents used to be joined in

Pangaea (meaning “all land”) that broke up into smaller continents, “drifted” to current locations

What patterns do we see in continent shapes?

Continental Drift - Wegener’s hypothesis of continent movement after Pangaea broke apart

Early evidence #1:Coastlines on early maps seem to fit like puzzle pieces

Why are there fossils of cynognathus on both Africa and South America and no where else?

“Continental Drift”, Early evidence #2

Fossils of the same organism were on opposite land masses (puzzle pieces), known to have been joined at one time

Why do rocks from Rhode Island and Scotland match?

“Continental Drift”, early evidence #3

Mountains and rocks continued on opposite puzzle pieces

Why did southern India used to have glaciers?

“Continental Drift”, early evidence #4

Misplaced glacial remnants

and tropical swamps can be

explained if continents were

once joined

Newer evidence

• Proof of seafloor spreading at the Mid-Atlantic Ridge (1947)– Rock at the ridge was dated much younger than

continental rock– Paleomagnetism also apparent • As magma solidifies, iron crystals align with

Earth’s magnetic field like a compass. Geologists have known that this happens periodically throughout history, as magnetic poles flip flop.

Modern Theory of Plate Tectonics

• Earth is made up of 9 primary plates and several microplates made up of continental and oceanic crust.– Upper lithosphere is crusty and moves about on

plasticy asthenosphere.– Asthenosphere moves most likely due to convection

in the mantle due to heat from core and radioactivity from mantle

• Where plates meet is called a plate boundary– Types: Convergent, divergent, transform

PLATE BOUNDARIES1. Convergent Boundary• Ocean – Continent• Ocean – Ocean• Continent – Continent

Continent – Continent convergence

Ocean – Continent Convergence

2. Divergent Boundary

3. Transform Boundary

Where in the World do we find those

boundaries?