Earth Structure

Mexico quake-- magnitude at 7.0, and epicenter was in the western Pacific state of Michoacan. Its depth was about 40 miles Mexico quake-- magnitude at 7.0, and epicenter was in the western Pacific state of Michoacan. Its depth was about 40 miles Indonesia-- earthquake off coast of Indonesia Wednesday, April 11 with magnitude of 8.6, sparking tsunami warnings Indonesia-- earthquake off coast of Indonesia Wednesday, April 11 with magnitude of 8.6, sparking tsunami warnings

Lithosphere Consists of continental, oceanic and upper part of mantle Consists of continental, oceanic and upper part of mantle Continents composed of granite-type rock, quartz and feldspar minerals, density+2.8g/cm 3 Oceanic crust formed of basalt; basalt rich in iron/magnesium minerals, density+3.0 g/cm 3 Lithosphere is rigid layer of crust and mantle overlying partially-molten asthenosphere

Why Continents Higher and Ocean Floor Lower Isostacy—Principle that less dense continental crust sits higher on the mantle while denser oceanic crust sits lower Isostacy—Principle that less dense continental crust sits higher on the mantle while denser oceanic crust sits lower 7qhUQZg&feature=player_detailpage 7qhUQZg&feature=player_detailpage 7qhUQZg&feature=player_detailpage 7qhUQZg&feature=player_detailpage

Continental Drift Evidence – Geographic fit of continents – Fossils – Mountains – Glaciation Evidence supporting the idea that the continents had drifted. Researchers noted geographic fit of continents – e.g. Africa and S. America – Atlantic formed by separation of Africa from S. America Seuss, 1885, proposed super continent by studying fossils, rocks, mountains Wegener and Taylor, early 1900’s, proposed continental drift and Pangaea

Continental Drift Geographic Fit Continents seem to fit together like pieces of a puzzle Continents seem to fit together like pieces of a puzzle

Continental Drift Fossils Similar distribution of fossils such as the Mesosaurus Similar distribution of fossils such as the Mesosaurus

Continental Drift Mountains Mountain ranges match across oceans Mountain ranges match across oceans

Continental Drift Glaciation Glacial ages and climate evidence Glacial ages and climate evidence

Objections to the Continental Drift Model Wegener did not provide a plausible mechanism to explain how the continents could have drifted. Wegener did not provide a plausible mechanism to explain how the continents could have drifted.

Seafloor Spreading Continental drift reexamined in 1960’s with new information Continental drift reexamined in 1960’s with new information – World seismicity New theory developed – Seafloor spreading Supporting evidence for seafloor spreading Theory combining continental drift and seafloor spreading termed “Plate Tectonics” – Volcanism – Age of seafloor – Heat flow – Paleomagnetism

Seafloor Spreading New sea floor created at the mid-ocean ridge and destroyed in deep ocean trenches New sea floor created at the mid-ocean ridge and destroyed in deep ocean trenches

Evidence for Seafloor Spreading World Seismicity Earthquake distribution matches plate boundaries Earthquake distribution matches plate boundaries

Evidence for Seafloor Spreading Volcanism Volcanoes match some plate boundaries; some are hot spots Volcanoes match some plate boundaries; some are hot spots

Evidence for Seafloor Spreading Age of Seafloor Youngest sea floor is at mid-ocean ridge Oldest sea floor away from mid-ocean ridge

Evidence for Seafloor Spreading Paleomagnetism When rocks cool at the Earth’s surface, they record Earth’s magnetic field (normal or reverse polarity) When rocks cool at the Earth’s surface, they record Earth’s magnetic field (normal or reverse polarity) Earth has a magnetic field - Probably caused by rotation of solid inner core in liquid outer core (both mostly Fe)

Evidence for Seafloor Spreading Paleomagnetism Paleomagnetic studies indicate alternating stripes of normal and reverse polarity at the mid-ocean ridge. Paleomagnetic studies indicate alternating stripes of normal and reverse polarity at the mid-ocean ridge.

Seafloor Spreading Heat Flow In 1960, convection currents were proposed as driving force to move continents In 1960, convection currents were proposed as driving force to move continents

Theory of Plate Tectonics John Tuzo Wilson combined ideas of continental drift and seafloor spreading into “Plate Tectonics” John Tuzo Wilson combined ideas of continental drift and seafloor spreading into “Plate Tectonics”

Principles of Plate Tectonics Earth’s outermost layer composed of thin rigid plates moving horizontally Earth’s outermost layer composed of thin rigid plates moving horizontally Plates interact with each other along their edges (plate boundaries) Plate boundaries have a high degree of tectonic activity – mountain building – earthquakes – volcanoes

Plate Boundaries Three types

Plate Boundaries Divergent Plates move away from each other Plates move away from each other New crust is being formed New crust is being formed

Divergent Plate Boundaries Examples East African Rift Mid-Atlantic Ocean Ridge

Plate Boundaries Convergent Plates are moving toward each other Plates are moving toward each other Crust is being destroyed Crust is being destroyed Three Types: Ocean-continent Ocean-continent Ocean-ocean Ocean-ocean Continent-continent Continent-continent

Convergent Plate Boundaries Examples Convergent Plate Boundaries Examples Mount Lassen, California Andes, South America Mount Fuji, Japan

Plate Boundaries Transform Plates slide past one another Plates slide past one another Crust is neither created nor destroyed Crust is neither created nor destroyed xxxxxxxxxxxxxxxxxxx

Transform Plate Boundaries Examples San Andreas Fault Calexico, California Carrizo Plains, Central California