2 Continental DriftIn 1915, Alfred Wegener ( ), a German meteorologist, wrote a book titled The Origin of Continents and Oceans.
3 Continental Drift Wegener proposed the idea of Pangaea A supercontinent that driftedapartWegener had some evidenceto support his theory which hecalled Continental Drift
4 Evidence of Continental Drift The continents fit together like a puzzleThere are fossils of ancient animals and plants on different continents and there were no land bridgesThe mountain ranges on different continents align with one anotherClimate changes: Tropical plant fossils found in non-tropical regions
7 Sea Floor SpreadingIn the early 1960s, Henry Hess ( ), a geologist and former commander of a Navy ship equipped with an echo sounder, used the profile of the sea floor to propose that it was spreading at the mid- ocean ridges.
8 Sea Floor SpreadingHot fluid from the mantle (called magma) enters the rise or valley and cools, creating new sea floor (also called oceanic crust).
9 Sea Floor SpreadingThe advent of Sonar allowed for mapping of the ocean floor.Hess, using sonar, discovered significant depth differences along ocean bottomHess explained the difference by proposing mountain ranges and Rift Valleys.He stated that the ocean floor must be spreading at the Rift Valleys, creating the depth differences
10 Mapping the Mid-Ocean Ridge The mid-ocean ridge is the longest chain of mountains in the world.Scientists mapped the mid-ocean ridge using sonar.Sonar is a device that bounces sound waves off underwater objects and records it.
11 Evidence of Sea Floor Spreading Age of the crust at mid ocean ridgesOlder crust further away from the ridge, young crust at the ridgeMagnetic reversals over geological timeAlternating patterns that align on either side of the ridgePillow rocks at rift valleysEvidence of magma rising
12 In the 1960s scientists found evidence that new material is erupting along the mid-ocean ridge. The presence of pillow shaped rocks has showed that molten material has erupted again and again.Pillow rocks are created when magma cools quickly at a mid ocean ridge.Pillow Rocks
13 Magnetic PatternsOver geologic time, the magnetic polarity of Earth has switched.Scientists believe the poles switch because of a magnetic interaction between the planet’s inner and outer core.
14 Magnetic Reversals in Crust Evidence in the rocks shows that Earth’s magnetic poles have reversed.The iron bits line up in an alternating pattern.The alternating pattern demonstrates crust movement
15 Age of the CrustDrilling into the sea floor shows evidence of the ages of the rocksThe closer you get to the mid-ocean ridge the younger the rock. The farther you get, the older the rock.This demonstrates a movement away from the ocean ridge
19 Convection at Mid-Ocean Ridge At a mid-ocean ridge, molten material rises from the mantle and erupts.The molten material spreads out, pushing the older rock away on either side of the ridge.This process continually adds to the ocean floor
20 Subduction in Deep-Ocean Trenches As the ocean spreads apart, it also plunges into deep water canyons called deep- ocean trenches.Subduction is the process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle.
21 SubductionThe processes of subduction and sea-floor spreading can change the size and shape of the oceans.Because of these processes, the ocean floor is renewed about every 200 million years.
22 Subduction in the Oceans The Pacific Ocean is shrinking! This is due to the fact that a deep-ocean trench is swallowing more crust than the mid-ocean ridge can produce.The Atlantic Ocean however, is expanding!
23 How Plates MoveThe Lithosphere is separated into 14 major plates and 32 minor platesThese plates move due to the convection currents occurring beneath themThe direction of their movement will have an effect on the surface of our planet
25 Three Types of Plate Boundaries DivergentConvergentTransform
26 Describing Plate Boundaries There are three main kinds of plate boundaries:divergentconvergenttransform
27 Plate Boundaries Place where 2 lithospheric plates meet Transform BoundariesPlace where 2 plates are sliding past each other in opposite directionsShearing stresses are causedDivergent BoundaryPlace where 2 plates are moving away from each other.Creates Rift Valleys and new crustOccur mostly at ocean floor
28 Convergent Boundaries Boundary where 2 plates move towards each other and collide.There are 3 types of convergent boundariesThey can occur as follows:Ocean crust to ocean crustOcean crust to continental crustContinental crust to continental crust
29 Convergent Boundaries Ocean to Ocean crust collideVolcanic Island Arcs createdOcean to Continental crust collideVolcanoes are created at the Subduction zonesContinental and Continental crust collideMountain ranges form due to similar densities of the continental crust (no Subduction)