Continental Drift and Plate Tectonics

Age of Earth estimates through time

Linnaeus

Wallace

Modern radioactive dating

Half life

Oldest fossil

Photoautotrophic prokaryote from Australia/South Africa (~3.5 bill yrs BP)

Alfred Wegener (1880-1930)

• Proposed the theory of continental drift in early 1900’s

• Who’s original idea?

• Antonio Snider-Pelligrini (1858)

• Mechanism not explained

Evidence

• Geologic

• Stratigraphic

• Paleoclimatic

• Paleontological

• Paleomagnetic

Geologic evidence

Continental slope fit

Distribution of earthquakes

Geologic evidence

Distribution of volcanoes

Geologic evidence

Geologic evidence

Mountain ranges

Matching sequence of rock strata on different continents

Precambrian shields Flood Basalts

Stratigraphic evidence

• Glacial deposits

• Scouring on rocks indicate the direction

Paleoclimatic evidence

Paleoclimatic evidence

Glossopteris fossil record

Paleontological evidence

Mesosaurus fossil record

Paleontological evidence

Paleomagnetic evidence

• Orientation of the magnetized crystals at the time of mineral formation

• Earth reverses its magnetic north at variable intervals

Paleomagnetic evidence

• Seafloor record of remnant magnetism (magnetic stripes)

• Every 104 – 106 years

Black - regular,

White – reversed

Computer models – 1965

Marine geology after WWII

• Oceanic floor samples

• Echo soundings

• Oceanic ridges

• Abysall plain

• Denser than continental

• < 150 my old

Continental Drift – continents were once united and have since become independent structures that have been displaced all over the globe

Plate Tectonics – study of the origin, movement and destruction of plates and how these events have been involved in the evolution of Earth’s crust

Plate tectonics

Crust Continental (felsic)

Oceanic (mafic)

Mantle

Lower lithosphere

Asthenosphere

Outer Core

Inner Core

Why is continental crust generally much older than the current oceanic crust?

Plate tectonics Ridge push

Mantle drag

Slab pull

Mid-oceanic ridge

Plate tectonics

19 major tectonic plates

Plate Boundaries

Divergent boundaries

Convergent boundaries

Transform boundaries

Tectonic history of the continents

Reconstruction of tectonic history

• Paleomagnetic declinations

• Symmetrical magnetic stripes

• Topographic and bathymetric maps

• Lithologic indicators of climate

Tectonic history of the continents Pangaea: ancient supercontinent (~250 mya)

Tectonic history of the continents

Break up of Pangaea (initiated 180 mya)

• Laurasia rifting

• Landbridges broken

• Gondwanaland

began to separate

Tectonic history of the continents

Most of Gondwanaland separated (100 mya)

Beringia ~75 mya

Tectonic history of the continents

Most of Gondwanaland separated (100 mya)

Landbridges btwn Europe and NA

Tectonic history of the continents • All continents separated (50 MYA)

• India about to collide with Eurasia (20 cm per year!)

Tectonic history of the continents Central American Landbridge ~3 mya

Great American Interchange

Formation of Isthmus of Panama – 3

MYA

North American ungulates, proboscids,

carnivorans, rodents dispersed south

South American ground sloths and

terror birds, armadillos dispersed north