Earth’s Structure

Origin of the Earth Meteors and Asteroids bombarded the EarthMeteors and Asteroids bombarded the Earth Earth is 4.6 billion years old

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

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

Earth’s Structure

Earth’s Layers

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

Continents Today

Continental Drift Theory In 1912 a German meteorologist and explorer named Alfred Wegener presented a theory that the continents were once joined together in one land mass and have over millions of years slowly drifted apart into their present positions as we see them today. He named the supercontinent “Pangaea” after the Greek word meaning “all land”. In 1912 a German meteorologist and explorer named Alfred Wegener presented a theory that the continents were once joined together in one land mass and have over millions of years slowly drifted apart into their present positions as we see them today. He named the supercontinent “Pangaea” after the Greek word meaning “all land”.

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 Theory Through Wegener’s research he found evidence to support his theory: Through Wegener’s research he found evidence to support his theory: Fossils of Glossopteris, a seed fern, was found in India, Australia, South America, Africa and Antarctica Fossils of Glossopteris, a seed fern, was found in India, Australia, South America, Africa and Antarctica Fossils of Mesosaurus, a small reptile were found in freshwater deposits in Africa & South America. Fossils of Mesosaurus, a small reptile were found in freshwater deposits in Africa & South America.

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

Glossopteris Fern Fern

Continental Drift Layers of the mountains found in S.E. Brazil, South America and S.W. Africa line up layer for layer in exact format. Layers of the mountains found in S.E. Brazil, South America and S.W. Africa line up layer for layer in exact format. Continents look like puzzle pieces that could fit together. Continents look like puzzle pieces that could fit together.

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 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