Continental Drift and Plate tectonics Our changing Planet Continental Drift and Plate tectonics

How has our view/Map of the world changed? Before Pythagoras proposed the world was round??? Before Christopher Columbus discovered America??? 1700’s – The continents were thought to have always been in one place.

What we “know” now Early 1900’s, Alfred Wegener (a German scientist) proposed the hypothesis of Continental Drift Continental Drift- All continents were once joined in a single landmass and have since drifted apart. Pangaea – supercontinent – means “all lands” He gathered lots of evidence to support his hypothesis Many other Scientists rejected his hypothesis because he could not give an explanation for the force that was moving the continents. He didn’t have a reason why the continents were moving.

What we “know”now Cont. New Technology leads to new discoveries – sea floor spreading Sonar (mid 1900’s – 1960’s) uses sound waves to map the ocean floor. Showed scientists that there is a chain of underwater mountains in the middle of the Atlantic Ocean. Harry Hess – proposed the idea of sea-floor spreading – the sea floor (Atlantic ocean floor) is spreading apart and new crust is being added

Evidence for Continental Drift and Sea Floor Spreading Group 1 – Land Features – p. 20 Group 2 – Fossils – p. 20 Group 3 – Climate – p. 21 Group 4 – Molten Material – p. 26 Group 5 – Magnetic Stripes – p. 26 Group 6 – Drilling samples – p. 27 Group 7 – Subduction – p. 28-29

Plate Tectonics The lithosphere is broken into separate sections called plates Theory of Plate tectonics – the Earth’s plates are in slow, constant motion, driven by convection currents in the mantle. Movement of Earth’s crustal plates can cause earthquakes, mountain formation, and volcanoes.

Plate tectonic cont. Fault – breaks in the Earth’s crust where rocks have slipped past each other 3 types of plate boundaries: Divergent – Plates move away from each other Convergent – Plates move towards each other Transform – Plates move side by side in opposite directions. When convection currents stop/heat source is removed, plate movements stop