Plate tectonic theory

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Plate Tectonics Theory 21/9/16

Continental Drift - the gradual movement of the continents across the earth's surface through geological time

Alfred Wegener - a single continent existed called - Pangaea

Pangaea then later split into 2 continents called - Laurasia and Gondawanaland

Evidence for this is from = fossils found either side of the Atlantic Ocean / land masses were once joined / Mountain ranges / Magam underground

Evidence 1 - Jigsaw Fit

Francis Bacon came up with the theory in 1620 that continents weren't static but actually moving

For example : Africa and South America having continents which appear to have once been togther

Evidence 2 - Geological Evidence

Similar types of rocks were present where continents appear to be connected

The rocks were likely to be formed under similar conditions

For example : in ancient cratons 2.6 billion years old

Evidence 3 : Biological Evidence

Fossils of the same species were found from continents which used to be connected

For example : the dinosaur Mesosaurus was found both in Africa and South America, however the creature was unlikely to migrate thousands of miles

Plant fossils were also found = Palm tree fossils found in Alaska which don't have the right growing conditions

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Evidence 4 : Sea floor spreading

Bathymetric maps formed in WW2 by sonar from submarines and mapped the sea floor

Patterns from the land were also seen in the sea as well

Palaeomagnetism - where new oceanic crust was created with symmetrical magnetic strips which aligned with Earth's magnetic field, provided permanent record of when the eruption happened

Evidence 5 : Seisometers / Subduction

In the 1940s Hugo Benioff realised that earthquakes came from specific points

Seisometers used in Cold War to detect underground weapon testing, but could also record earthquakes

Movement of seismic waves reveal parts of mantle which are solid and liquid

Evidence 6 : Hotspots

Plates move over stationary hotspots

Move over separate mantle plumes

For example : the Pacific plate moving other the Hawaiian fixed hotspot at 7cm per year

In 1928 Arthur Holmes, came up with convection currents

They were as a result of Radioactive decay in the Earth's core could generate heat to produce convection currents