Chapter 10 Continental drift- from controversial hypothesis to respectable theory. When conducting a scientific investigation there are two key questions that need to be asked- Whats happening? Whats happening? What causes this to happen? What causes this to happen? To answer this first question what must the investigator do? Look for patterns. Look for patterns. There are several observed patterns that led to the theory of continental drift which include: Jigsaw-puzzle fit of continents. Jigsaw-puzzle fit of continents. Remarkable similarity of rocks and rock assemblages on opposite sides of the Atlantic. Remarkable similarity of rocks and rock assemblages on opposite sides of the Atlantic. Remarkable similarity of geologic structures on the outer continental margins. Remarkable similarity of geologic structures on the outer continental margins. Similarities of fossils on opposite sides of the Atlantic. Similarities of fossils on opposite sides of the Atlantic. Jigsaw-puzzle fit of continents. Observable jigsaw-puzzle fit of the coasts on both sides of the Atlantic look as if the Americas, Europe, and Africa were at one time assembled together. Observable jigsaw-puzzle fit of the coasts on both sides of the Atlantic look as if the Americas, Europe, and Africa were at one time assembled together. Parallelism of facing shores of the Atlantic first noticed by Sir Francis Bacon-an English philosopher- scientist. Parallelism of facing shores of the Atlantic first noticed by Sir Francis Bacon-an English philosopher- scientist. Remarkable similarity of rocks and rock assemblages. Remarkable similarity of rocks and rock assemblages. Geographic match up of ancient crystalline rocks in adjacent regions of South America, Africa, North America and Europe discovered. Geographic match up of ancient crystalline rocks in adjacent regions of South America, Africa, North America and Europe discovered. Rock units of these adjacent areas were the same age. Rock units of these adjacent areas were the same age. Rock assemblages of adjacent coastlines parallel each other. Rock assemblages of adjacent coastlines parallel each other. Remarkable similarity of geologic structures. distribution of Permian glacier deposits found in South America, Africa, India, Antarctica and Australia.Difficult to explain in terms of separate glaciers- some close to the equator. distribution of Permian glacier deposits found in South America, Africa, India, Antarctica and Australia.Difficult to explain in terms of separate glaciers- some close to the equator. A single continental glacier could account for all these glacier deposits. A single continental glacier could account for all these glacier deposits. Mountain chains that ended at the coastline of one continent and seemed to continue on the edge of another continents coastline across the ocean (e.g. Appalachians match up with mountains in Greenland and northern Europe). Mountain chains that ended at the coastline of one continent and seemed to continue on the edge of another continents coastline across the ocean (e.g. Appalachians match up with mountains in Greenland and northern Europe). Similarities of fossils on opposite sides of the Atlantic. Fossils of the late freshwater Paleozoic reptile Mesosaurus were found in South America and Africa and nowhere else in the world. Fossils of the late freshwater Paleozoic reptile Mesosaurus were found in South America and Africa and nowhere else in the world. How could this reptile be found on opposite ends of the Atlantic? What is the second question that is asked during a scientific investigation? What causes these patterns to happen? What causes these patterns to happen? In 1912 a German meteorologist - Alfred Wegener set out to explain the event that led to these patterns. His explanation was a geologic event known as continental drift. Wegener suggested that all continents were once one. Wegener suggested that all continents were once one. This giant super continent was called Pangaea (Greek for all lands)*onstructions.htmlonstructions.html Pangaea broke into two parts Laurasia Laurasia broke to the north broke to the north Gondwanaland Gondwanaland broke to the south broke to the south This theory of continental drift was ignored by most of the scientific community at this time. The reason was a plausible driving force that could split up Pangaea could not be found. Plate Tectonics Chapter 4 Section 2 Plate Tectonics The study of the movement of the earths surface The study of the movement of the earths surface Earth structure Outer Layers Plate Tectonic Theory Earth is made up of as many as 30 lithospheric plates with 7 or 8 major plates which move slowly on top of the mantle. Earth is made up of as many as 30 lithospheric plates with 7 or 8 major plates which move slowly on top of the mantle. There are two types of plates, oceanic and continental. There are two types of plates, oceanic and continental. lithosphere from the Greek, lithos, stone from the Greek, lithos, stone the rigid outermost layer made of crust and uppermost mantle the rigid outermost layer made of crust and uppermost mantle asthenosphere from the Greek, asthenos, devoid of force from the Greek, asthenos, devoid of force the part of the mantle that flows like putty when put under pressure the part of the mantle that flows like putty when put under pressure Plate Boundaries Tectonic Plates 2 Types of Crust 1. Ocean Crust 1. Ocean Crust 2. Continental Crust 2. Continental Crust 2 Types of Crust Ocean Crust Ocean Crust Thin Dense Young Common rock- Basalt 2 Types of Crust Continental Crust Continental Crust Thick Not Dense Old Common rock- Granite Three types of PLATE BOUNDARIES Divergent plate boundary Divergent plate boundary Thingvellir fissure A fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge. A fissure zone (in shadow) that is the on-land exposure of the Mid-Atlantic Ridge. Divergent plate boundaries (spreading) Mid ocean ridge Mid ocean ridge Mid-Atlantic ridge Mid-Atlantic ridge Juan De Fuca ridge Juan De Fuca ridge Rift valley Rift valley Red Sea Red Sea 2 nd boundary type Convergent plate boundary, where one plate collides with another, of which there are three possibilities Convergent plate boundaries (colliding) oceanic to oceanic collisions oceanic to oceanic collisions result in chains of volcanic islands/forms trenches result in chains of volcanic islands/forms trenches Aleutian Islands Aleutian Islands Convergent plate boundaries (colliding) oceanic to continental oceanic to continental results in volcanic mountains; oceanic plate slides under results in volcanic mountains; oceanic plate slides under Convergent plate boundaries (colliding) Andes Mountain Range Andes Mountain Range Convergent plate boundaries (colliding) continent to continent continent to continent collision results in nonvolcanic mountains collision results in nonvolcanic mountains Himalayas Himalayas 3 rd type of boundary Transform plate boundary Transform plate boundaries (shearing) results in a lateral fault results in a lateral fault San Andreas San Andreas Ridge where spreading takes place between plates where spreading takes place between plates mid Atlantic ridge mid Atlantic ridge Juan de Fuca ridge Juan de Fuca ridge Trench Where plates collided and one is pushed under the other Where plates collided and one is pushed under the other Aleutian Trench Aleutian Trench Mariana Trench Mariana Trench Fault Zone Where two plates slide against each other Where two plates slide against each other San Andreas fault San Andreas fault Causes of Plate Motion Convection, the transfer of heat through the movement of heated material (think of boiling water). Convection, the transfer of heat through the movement of heated material (think of boiling water). Density Changes With Temperature Higher temperature = less dense (rises). Higher temperature = less dense (rises). Lower temperature = more dense (falls). Lower temperature = more dense (falls). This cycle is called a convection current. This cycle is called a convection current. Mantle Convection Convection currents in the mantle rise beneath oceanic ridges, spread laterally carrying plates along, and then decend at subduction zones where oceanic plates dive into the mantle. Continents, being less dense, are not subducted. Evidence for this is shown by higher heat flows measured at oceanic ridges. Convection currents in the mantle rise beneath oceanic ridges, spread laterally carrying plates along, and then decend at subduction zones where oceanic plates dive into the mantle. Continents, being less dense, are not subducted. Evidence for this is shown by higher heat flows measured at oceanic ridges. Suspect Terranes Terranes are pieces of lithosphere, each with its own distinct geologic history. We think that continents are formed, and grow over time, by the addition of terranes. Terranes are pieces of lithosphere, each with its own distinct geologic history. We think that continents are formed, and grow over time, by the addition of terranes. Moved by Seafloor Spreading Blocks of terranes are then added to continents where subduction is occurring. Blocks of terranes are then added to continents where subduction is occurring. Western North America Much of the continent is a patchwork of terranes. Much of the continent is a patchwork of terranes. The End
