BEFORE PANGAEA

EPSC 510 // PRESENTATION 1

CURRENT THEORY

• Plate tectonics -- Earth’s continental and oceanic crusts divided into plates

• Convection from inner Earth causes movement of plates//tectonic activity

• Earthquakes, mountain ranges, volcanic activity, ocean trenches, etc.

• Outcome: the geological landscape we know today

History

• Alfred Wagner -- 1912 -- theory of continental drift -- later developed into theory of plate tectonics

• Supercontinent Rodinia (~1 Ga) fragmented into smaller continents, then reassembled into…

• Supercontinent Pangaea (~300 - 225 Ma) fragmented into two smaller continents…

• Laurasia and Gondwana (~200 Ma) fragmented into…

• Current layout of continents on Earth

Proof• Shapes of continents -- jig-saw puzzle

• Fossil comparison -- species similarity at distant continental boundaries

• Geo-sequences -- similar deposits at distant boundaries

• Paleomagnetism -- polar wandering paths

• Position of plate boundaries -- location of major seismic, volcanic, geothermal activity

• Mid-Ocean Ridges -- clear indicators of mantle convection (driving force of tectonics)

• Quantitative measurements of plate movement -- a few cm/yr

But where did the tectonic plates come from?

• Theory of plate tectonics implies a dynamic Earth through time -- future, present and past

• Why do we assume supercontinents were the beginning? Did they just appear out of thin air?

Cratons• Cratons -- building blocks of continents, often found in interior of

tectonic plates

• Very old stable basement rock which roots deep into the lithosphere -- older than oceanic lithosphere

• These cratons supposedly formed during the Archean

• At this time, the Earth was much hotter -- greater heat flow, less viscous mantle -- high turnover of oceanic crust

• Continental evolution -- many steps before Pangaea

• “The Early Earth and Plate Tectonics” -- http://www.youtube.com/watch?v=QDqskltCixA