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When explorers and mapmakers crossed the Atlantic Ocean in the 1600s, some of them noticed something puzzling. The more complete their maps became, the more the Atlantic Ocean shorelines of the Americas and the Old World continents of Africa and Europe looked like pieces of jigsaw puzzle. Until 1912, Alfred Wegener proposed that the continents we see are the broken fragments of a single landmass that he called Pangaea. He hypothesized that over millions of years the continents slowly moved to their present positions. Plate Tectonics
Earth’s Interior • Geologists use two main ways of gathering evidence to gain insight on Earth’s Interior: • Direct Evidence from rock samples. • Indirect Evidence from seismic waves. • Seismic waves are produced by earthquakes. Geologists record the seismic waves and study how they travel through Earth.
Earth’s Interior • The three main layers of Earth are the crust, the mantle, and the core. These layers vary greatly in size, composition, temperature and pressure. • As you travel to the center temperature and pressure increase. • The temperature in the core is estimated at 5,426.7o C or 9,800o F. • The pressure in the core is estimated at 330 to 360 gigapascals.
Earth’s Interior • Earth’s Interior is broken up into 5 layers. • Crust- Outer most layer of Earth • Moho- Boundary between the crust and the mantle. • Mantle- Extends from the bottom of the crust to a depth of about 2900 km (1800mi). • Outer Core- Layer of molten metal. • Inner Core- Dense ball of solid metal.
The Crust • Layer of rock that forms Earth’s outer skin. The crust is a layer of solid rock that includes continental crust and oceanic crust. • Oceanic Crust: Primarily made up of basalt and is more dense than continental crust. • Continental Crust: Primarily made up of granite and is less dense than oceanic crust.
Mantle • Made up of very hot but solid rock. Geologists divide the mantle based on physical characteristics. • Lithosphere: Uppermost part of the Mantle and Crust form this rigid layer. • Moho: Boundary between Crust and Mantle; Seismic Waves increase in speed. • Asthenosphere: Plastic part of the Mantle. • The Lower Mantle: Beneath the Asthenosphere, extends to the Outer Core.
The Core • The Core is made mostly of the metals iron and nickel. • The Outer Core is roughly 2,867 km thick. Scientists have discovered that certain seismic waves cannot pass through liquids and have confirmed that the inner core is liquid. • The Inner Core is a solid dense ball. It is solid due to the immense pressure.
Heat Transfer • Heat always moves from a warmer substance to a cooler substance. There are three types of heat transfer: • Radiation- Transfer of energy through space. • Conduction- Heat transfer within a material or between materials that are touching. • Convection- Transfer of heat through movement of current through fluids.
Heat Transfer- Convection • Heat transferred by convection is caused by differences of temperature and density. • When a liquid or gas is heated the particles move faster and spread apart. As a result, the particles of the heated fluid occupy more space; decreasing density. • Then when a fluid cools, its particles move more slowly and compact; increasing density.
Convection Currents • A convection current is the flow that transfers heat within a fluid. • Heating and cooling of the fluid, changes in the fluids density, and the force of gravity combine to set a convection current in motion.
Convection Currents in Earth • In Earth’s mantle, large amounts of heat are transferred by convection currents. • Heat from the core and mantle itself causes convection currents inside the mantle.
Drifting Continents • Alfred Wegener was the first scientist to hypothesize (correctly) that Earth’s continents moved. • His idea that the continents SLOWLY moved over Earth’s surface became known as continental drift. • Wegener supported his hypothesis with evidence from land features, fossils and climate change.
Continental Drift: Land Feature Evidence • Mountain chains of North America, Great Britain, and Scandinavia all can be dated to same time period, and have similar rock types. Same occurrence between the mountain chains of South America and Africa. • Evidence of glaciation striations in parts of Southern South America, Africa, Madagascar, India, Australia and Antarctica.
Continental Drift: Fossil Evidence • Glossopteris was a fern like planet that lived 250 mya and its fossils have been found in South America, Africa, India, Antarctica and Australia. • Fresh water reptile Mesosaurus that lived 300 myaand its fossil can be found on the eastern side of South America and the western side of Africa.
Continental Drift: Climate Evidence • As the continents drifted, their climate also changed. Scientists have also found coral reef beds in places around Poland, in the Siberian desert in Russia, China, Romania, Chicago and BUFFALO! • Buffalo was a tropical paradise a few million years ago; as were all these places that are not anymore because the continent has changed position.
Mid-Ocean Ridges • Mid-Ocean Ridges are undersea mountain chain where new ocean floor is produce. Scientists discovered these ridges while mapping the sea floor using sonar. • Henry Hess proposed that an idea in 1960 that would help support Wegener’s hypothesis (Geologists discredited Wegener’s ideas). Henry Hess proposed the mechanic that produced mid-ocean ridges.
Sea-Floor Spreading • Sea-Floor Spreading continually adds new material to the sea floor. • The sea floor spreads apart along both sides of a mid-ocean ridge as new crust is added. • As a result, the ocean floor move like conveyor belts, carrying the continents along with them.
Evidence for Sea-Floor Spreading • Molten Material- Molten rock erupts through the valleys that run along the center of the mid-ocean ridge. The rock hardens to form new oceanic crust. • Magnetic Strips- Earth’s Magnet pole have reversed themselves and the new crust aligns it self to the North and South Poles. Scientists discovered that the rock that makes up the ocean floor lies in a pattern of magnetized strips.
Evidence for Sea-Floor Spreading • Drilling Samples: Geologists drilled into the sea floor and noticed that the age of the rock was always that the young rock were always in the center of the ridge and the further you went from the ridge the older the rock became.
Subduction at Trenches • The amount of crust is not increasing so while the sea-floor is spreads at mid-ocean ridges; the ocean floor also plunges into deep under water canyons called deep-ocean trenches. • In a process that takes millions of years, part of the ocean floor sinks back into the mantle at deep-ocean trenches.
Process of Subduction • Subduction is the process by which ocean floor sinks beneath a deep ocean trench and back into the mantle. • Subduction and Sea-Floor Spreading change the size and shape of the oceans. • The ocean floor is renewed about every 200 million years.
Theory of Plate Tectonics • J.Tuzo Wilson proposed that the lithosphere is broken into separate sections called plates. • Wilson combined the evidence from Sea-Floor spreading, Earth’s plates and continental drift into the theory of plate tectonics. • The theory of plate tectonics states that pieces of Earth’s lithosphere are in slow, constant motion, driven by the convection currents in the mantle.
Plate Boundaries • The edge of Earth’s plates meet at plate boundaries. Plate boundaries extend deep into the lithosphere. • Along these boundaries, cracks can form which happen when Earth’s crust have slipped past one another. These breaks in the boundaries are called faults.
Plate Boundaries • There are three types of boundaries that form along Earth’s plates. Each one unique due to type of plate movement that occurs there: • Divergent Boundaries: When two plates move apart or diverge. • Convergent Boundaries: When two plates come together or converge on one another. • Transform Boundaries: When two plates slide past one another.
