Formation of the Earth

Previous Theories  Continental Drift Theory  Developed by Alfred Wegner (1900’s)  Believed continents were once all combined into one landmass he called Pangaea meaning “All Earth”  Continents seemed to fit together like a jigsaw puzzle  Explained why fossils of the same plants and animals are found on the coast of Africa and South America  Continental Drift Theory  Developed by Alfred Wegner (1900’s)  Believed continents were once all combined into one landmass he called Pangaea meaning “All Earth”  Continents seemed to fit together like a jigsaw puzzle  Explained why fossils of the same plants and animals are found on the coast of Africa and South America

Pangaea

More Theories  Sea Floor Spreading (1950’s)  Cracks in the ocean floor spread apart allowing magma to rise and create new ocean crust  This helped explain underwater mountain ridges that were found at the bottom of oceans  Sea Floor Spreading (1950’s)  Cracks in the ocean floor spread apart allowing magma to rise and create new ocean crust  This helped explain underwater mountain ridges that were found at the bottom of oceans

Mapping the World’s Oceans

Plate Tectonics  Current theory of earth formation (1960’s)  Lithosphere is divided in plates that move along the magma of the asthenosphere  Scientists don’t know exactly what causes the plates to move  Current theory of earth formation (1960’s)  Lithosphere is divided in plates that move along the magma of the asthenosphere  Scientists don’t know exactly what causes the plates to move

Possible Forces that Cause Plate Movement  Ridge Push – gravity causes the oceanic lithosphere to sink into the asthenosphere

Ridge Push

Possible Forces that Cause Plate Movement  Slab pull - because the oceanic lithosphere is denser than the asthenosphere the edge sinks and pulls the rest of the tectonic plate with it

Slab Pull

Possible Forces that Cause Plate Movement  Convection – hot rock deep in the Earth rises while cooler rock sinks, which causes the oceanic lithosphere to move sideways away from the oceanic ridge

Convection