Mini Quiz What happens in Earth’s interior to produce Earth’s magnetic field? 2. Rocks on continents are billions of years old, while the oldest rock found on the ocean floor is less than 200 million years old. Explain how this is possible. NOTE: DYNAMIC EARTH TEST MAY 10, 2007

Geomagnetism

Dynamic Earth

Earth’s Interior Core – dense – Iron and Nickel – Inner Core - solid – Outer Core - liquid – Less dense than core – Iron and Magnesium silicates – Mostly solid – Upper mantle is partially molten Mantle – Outermost layer – Very thin and rigid – Continental – granite – Density = 2.8 g/cm 3 – Oceanic – basalt – Density = 3.0 g/cm 3 Crust

mantle convection Heat transfer from the core to the mantle produces slow convection of the mantle material (in the order of centimetres per year)

Mantle convection produces lateral forces at the boundary between the mantle and the crust

Lateral forces at the crust- mantle boundary push the crust around – in different directions – and this leads to the motion of crustal plates. The plates are moving at rates of cm/year

Evidence of Internal Structure Granite Density Density – calculate density of Earth – Speculate on probable compositions Basalt Meteorites Meteorites – Use composition and age to determine composition and age of Earth Seismic waves Seismic waves – Travel times and direction give indication of internal structure of Earth

Types of Seismic Waves S waves S waves P waves P waves – Primary waves – Push and pull movement – Travel fastest (~ 6 km/sec) – Travel thru solids and liquids – Secondary waves – Move side-to-side – Slower (~ 4 km/sec) – Travel thru solids only

Seismic Waves Through Earth

Lithosphere Consists of continental, oceanic and upper part of mantleConsists of continental, oceanic and upper part of mantle Continents composed of granite- type rock, quartz and feldspar minerals, density+2.8g/cm 3Continents 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 3Oceanic 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 asthenosphereLithosphere is rigid layer of crust and mantle overlying partially-molten asthenosphere

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

Continental Drift Model Problems Alfred Wegener Alfred Wegener – Did not provide a plausible mechanism to explain how continents drifted – Presented research to professionals

Seafloor Spreading Continental drift reexamined in 1960’s with new informationContinental drift reexamined in 1960’s with new information – World seismicity New theory developed – Seafloor spreadingNew theory developed – Seafloor spreading Supporting evidence for seafloor spreadingSupporting evidence for seafloor spreading Theory combining continental drift and seafloor spreading termed “Plate Tectonics”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) 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

Seafloor Spreading Convection Currents In 1960, proposed as driving force to move continents In 1960, 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 horizontallyEarth’s outermost layer composed of thin rigid plates moving horizontally Plates interact with each other along their edges (plate boundaries)Plates interact with each other along their edges (plate boundaries) Plate boundaries have high degree of tectonic activityPlate boundaries have high degree of tectonic activity – mountain building – earthquakes – volcanoes

Plate Boundaries Three types DivergentDivergent ConvergentConvergent TransformTransform

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 Three Types: Ocean-continent Ocean-continent Ocean-ocean Ocean-ocean Continent-continent Continent-continent Crust is being destroyed Crust is being destroyed

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