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Inside the Earth Reflections 10/13 – Describe the inside of the Earth. 10/14 – Name the 6 layers of the Earth. 10/17 – Explain why the plates move. Earth Layers • The Earth is divided into 6 main layers. Inner Core Outer Core Inner Mantle Outer Mantle Crust – Oceanic and Contential The Layers of the Earth © Copyright 2006. M. J. Krech. All rights reserved. The Crust • The crust makes up 1% of the Earth. • The crust of the Earth is broken into many pieces called plates. • Brittle rocks – Silicon, aluminium, iron, calcuim, sodium, potassium, and magnesium The Crust The crust is composed of two rocks. The continental crust is mostly granite. The oceanic crust is basalt. Basalt is much denser than the granite. Because of this the less dense continents ride on the denser oceanic plates. The Crust • Outer layer • 5-100 km thick • 2 types of crust – Oceanic (very dense, made of basalt) – Continental (less dense, made of granite) Types of Crust Oceanic crust – 7 Km thick Made of dense igneous rock More dense Continental crust – 40 km thick Larger – under mountains Less dense Oceanic and Continental Crust The Mantle • The mantle is the layer below the crust. • The mantle is the largest layer of the Earth. • The mantle is divided into two regions: the upper and lower sections The Lithosphere The crust and the upper layer of the mantle together make up a zone of rigid, brittle rock called the Lithosphere. The Lithospheric Plates The crust of the Earth is broken into many pieces called plates. The plates "float" on the soft, semirigid asthenosphere. Upper Mantle • 670 KM below the surface • Rocks are brittle and solid • Make up the lithosphere • CRUST AND UPPER MANTLE MAKE UP THE LITHOSPHERE LOWER MANTLE • 2900 KM below the surface • The rocks become soft below the upper mantle. • Convection currents can occur because of this fact. • Loose SOLID • Magnesium and iron The Mantle The middle mantle is composed of very hot dense rock. The asthenosphere is the reason that the crustal plates of the Earth move. Asthenosphere- Partial melted layer of the mantle. Plates float on the asthenosphere. The Asthenosphere The asthenosphere is the semi-rigid part of the middle mantle that flows like hot asphalt under a heavy weight. Convection Currents The middle mantle "flows" because of convection currents. Convection currents are caused by the very hot material at the deepest part of the mantle rising, then cooling and sinking again --repeating this cycle over and over. Convection Currents The next time you heat anything like soup or water in a pan you can watch the convection currents move in the liquid. When the convection currents flow in the asthenosphere they also move the crust. Currents created by uneven heating of substances. ! Tectonic Plates • Earth’s crust is broken into about 19 pieces • These plates move on top of the asthenosphere The Core • Made mostly of iron • 1/3 of the earth’s mass • Very hot The Outer Core The core of the Earth is like a ball of very hot metals. The outer core is so hot that the metals in it are all in the liquid state. The outer core is composed of the melted metals of nickel and iron. Outer Core • The outer core is liquid. The outer core is made up of iron and is very dense. The Earth’s magnetic field is contained in the outer core. 5500 KM below surface Inner Core The inner core of the Earth has temperatures and pressures so great that the metals are squeezed together and are not able to move. The inner core is a solid. 6,370 KM below the surface The Inner Core The inner core of the Earth has temperatures and pressures so great that the metals are squeezed together and are not able to move about like a liquid, but are forced to vibrate in place like a solid. Physical Structure of the Earth (5 Layers) • Lithosphere- rigid outer layer (crust) • Asthenosphere- solid rock that flows slowly (like hot asphalt) • Mesosphere- middle layer • Outer Core- liquid layer • Inner Core- solid, very dense The Structure of the Earth and Plate Tectonics The Crust • This is where we live! • The Earth’s crust is made of: Continental Crust Oceanic Crust - thick (10-70km) - buoyant (less dense than oceanic crust) - mostly old - thin (~7 km) - dense (sinks under continental crust) - young How do we know what the Earth is made of? • Geophysical surveys: seismic, gravity, magnetics, electrical, geodesy – Acquisition: land, air, sea and satellite – Geological surveys: fieldwork, boreholes, mines Aim: How do Continents Drift? I. The Continental Drift Theory - proposed by Alfred Wegener - theorized that the continents floated around the planet and moved through the oceans. * ~ 300 mya the continents were all together forming what was called Pangaea = “All Land” The Continental Drift Theory 1. Wegener believed the landmasses could all fit together. 2. Wegener did not have enough hard evidence or proof to support his ideas. 3. It took until the 1960’s for new evidence to emerge. 4. Fossils of Glossopteris (a fern plant) are found on many continents. Scientists think the seeds were too large to be carried by wind, and therefore, could not explain how it traveled the great distances between the continents today. This indicates the continents must have been closer. 5. Fossils of Lystrosaurus (swamp-dwelling hippo-like creature) are found on many continents. Scientists do not believe this creature could have swam the great distances between the continents today. This indicates the continents must have been closer. II. Evidence for Continental Drift 1. The Continental Puzzle continents fit together like a giant puzzle 2. Matching Fossils - Fossils of the same organisms (plants and animals) are found on different continents. 3. Rock Types and Structures - different mountain ranges across the ocean have the same rock composition and age. Present (2013) 250 Million Years ago Pangaea IV. A New Theory Emerges Theory of Plate Tectonics suggests that the Earth’s surface is composed of rigid plates that move, carrying the continents. (uses Wegner’s evidence) Plate Tectonics What is Plate Tectonics? • If you look at a map of the world, you may notice that some of the continents could fit together like pieces of a puzzle. Plate Tectonics • The Earth’s crust is divided into 12 major plates which are moved in various directions. • This plate motion causes them to collide, pull apart, or scrape against each other. • Each type of interaction causes a characteristic set of Earth structures or “tectonic” features. • The word, tectonic, refers to the deformation of the crust as a consequence of plate interaction. World Plates What are tectonic plates made of? • Plates are made of rigid lithosphere. The lithosphere is made up of the crust and the upper part of the mantle. What lies beneath the tectonic plates? • Below the lithosphere (which makes up the tectonic plates) is the asthenosphere. Plate Movement • “Plates” of lithosphere are moved around by the underlying hot mantle convection cells What happens at tectonic plate boundaries? Three types of plate boundary • Divergent • Convergent • Transform Divergent Boundaries • Spreading ridges – As plates move apart new material is erupted to fill the gap Age of Oceanic Crust Courtesy of www.ngdc.noaa.gov Iceland: An example of continental rifting • Iceland has a divergent plate boundary running through its middle Convergent Boundaries • There are three styles of convergent plate boundaries – Continent-continent collision – Continent-oceanic crust collision – Ocean-ocean collision Continent-Continent Collision • Forms mountains, e.g. European Alps, Himalayas Himalayas Continent-Oceanic Crust Collision • Called SUBDUCTION Subduction • Oceanic lithosphere subducts underneath the continental lithosphere • Oceanic lithosphere heats and dehydrates as it subsides • The melt rises forming volcanism • E.g. The Andes Ocean-Ocean Plate Collision • When two oceanic plates collide, one runs over the other which causes it to sink into the mantle forming a subduction zone. • The subducting plate is bent downward to form a very deep depression in the ocean floor called a trench. • The worlds deepest parts of the ocean are found along trenches. – E.g. The Mariana Trench is 11 km deep! Transform Boundaries • Where plates slide past each other Above: View of the San Andreas transform fault Practical Exercise 2 Where will the UK be in: 1,000 years? 1,000,000 years? 1,000,000,000 years? Volcanoes and Plate Tectonics… …what’s the connection? Pacific Ring of Fire Volcanism is mostly focused at plate margins Volcanoes are formed by: - Subduction - Rifting - Hotspots Pacific Ring of Fire Hotspot volcanoes What are Hotspot Volcanoes? • Hot mantle plumes breaching the surface in the middle of a tectonic plate The Hawaiian island chain are examples of hotspot volcanoes. Photo: Tom Pfeiffer / www.volcanodiscovery.com The tectonic plate moves over a fixed hotspot forming a chain of volcanoes. The volcanoes get younger from one end to the other. • As with volcanoes, earthquakes are not randomly distributed over the globe Figure showing the distribution of earthquakes around the globe • At the boundaries between plates, friction causes them to stick together. When built up energy causes them to break, earthquakes occur. Where do earthquakes form? Figure showing the tectonic setting of earthquakes Plate Tectonics Summary • The Earth is made up of 3 main layers (core, mantle, crust) • On the surface of the Earth are tectonic plates that slowly move around the globe • Plates are made of crust and upper mantle (lithosphere) • There are 2 types of plate • There are 3 types of plate boundaries • Volcanoes and Earthquakes are closely linked to the margins of the tectonic plates