Planet EarthSection 1 SECTION 1: EARTH’S INTERIOR AND PLATE TECTONICS Topics of section: KEY IDEAS 〉 How is Earth’s interior structured? 〉 How has the appearance of Earth changed over time? 〉 What geologic features are common near tectonic plate boundaries? What is Earth’s Interior Like? Plate Tectonics Plate Boundaries Divergent Boundaries

Planet EarthSection 1 A peach can be used as a model for some aspects of Earth’s structure. Compare the drawing of the cross section of the peach below with the cross section of Earth, and answer the following questions. Copy the diagram of the Earth

Planet EarthSection 1 1.Describe the outer layer of the peach (the skin). What aspect of Earth’s structure does the outer layer of the peach represent? 2.The peach pulp is the next layer. How would you describe it? What aspect of Earth’s structure does the peach pulp represent? 3.The pit is the innermost part of the peach. What is the pit like? What aspect of Earth’s structure does the peach pit represent?

Planet EarthSection 1 WHAT IS EARTH’S INTERIOR LIKE? 〉 How is Earth’s interior structured? 〉 Earth’s interior is made up of several distinct compositional layers. CRUST: the thin and solid outermost layer of Earth above the mantle MANTLE: the layer of rock between Earth’s crust and core

Planet EarthSection 1 VISUAL CONCEPTS: STRUCTURE OF THE EARTH

Planet EarthSection 1 WHAT IS EARTH’S INTERIOR LIKE? CONTINUED Earth’s interior gets warmer with depth. Earth’s core is nearly as hot as the surface of the sun.  Earth’s core is composed mainly of nickel and iron.  The inner core is thought to be solid and metal.  The outer core is thought to be made of liquid metal. CORE: the center part of the Earth below the mantle

Planet EarthSection 1 VISUAL CONCEPT: FORMATION OF EARTH’S CRUST, MANTLE, AND CORE

Planet EarthSection 1 WHAT IS EARTH’S INTERIOR LIKE? CONTINUED Radioactivity contributes to high internal temperatures.  The breakdown of radioactive isotopes uranium, thorium and potassium give off energy that contributes to Earth’s high internal temperatures.  Temperatures in the mantle can reach more than 1250 °C.  The core may reach temperatures above 5000 °C.

Planet EarthSection 1 PLATE TECTONICS 〉 QUESTION: How has the appearance of Earth changed over time? 〉 ANSWER: Alfred Wegener hypothesized that all of the continents might have been part of one landmass in the past before they drifted apart. Pangaea.  Wegener pieced the continents together like a puzzle and called the supercontinent they formed Pangaea.  Wegener found nearly identical fossils on widely separate continents, which supported his idea.

Planet EarthSection 1 VISUAL CONCEPT: CONTINENTAL DRIFT (PANGAEA)

Planet EarthSection 1 PLATE TECTONICS, CONTINUED Evidence for Wegener’s ideas came later.  Wegener’s theory of continental drift was ignored until structures discovered on the ocean floor provided evidence for a mechanism for the movement of continents.  Symmetrical bands on either side of a mid-ocean ridge indicate that the two sides of the ridge were moving away from each other and new ocean floor was rising up between them. Continental drift was ignored until symmetrical bands on either side of the mid- ocean ridge showed that they were moving away from each other. New floor was rising up.

Planet EarthSection 1 EVIDENCE FOR CONTINENTAL DRIFT

Planet EarthSection 1 PLATE TECTONICS, CONTINUED Alignment of oceanic rocks supports the theory of moving plates.  Iron in molten rock aligns itself with Earth’s magnetic field as it cools.  The Earth’s magnetic field reverses polarity about every 200,000 years.  The process is recorded as magnetic bands in rock, based on the age of the rock.  Symmetrical bands on either side of the Mid Atlantic Ridge suggest that the crust was moving away from the ridge.

Planet EarthSection 1 PLATE TECTONICS, CONTINUED Earth has plates that move over the mantle.  The crust and upper portion of the mantle are divided into about seven large pieces called tectonic plates. lithosphere: the solid outer layer of Earth that consists of the crust and the rigid upper part of the mantle plate tectonics: the theory that explains how large pieces of the lithosphere, called plates, move and change shape

Planet EarthSection 1 TECTONIC PLATES

Planet EarthSection 1 PLATE TECTONICS, CONTINUED Scientists do not understand exactly what makes tectonic plates move.  One hypothesis suggests that plate movement results from convection currents in the asthenosphere, the hot, fluid portion of the mantle.  Another hypothesis suggests that plate movement results from the force of gravity acting on the plates.

Planet EarthSection 1 PLATE BOUNDARIES 〉 What geologic features are common near tectonic plate boundaries? 〉 Volcanoes 〉 Earthquakes 〉 Mountains 〉 Rift Valleys 3 types of Boundaries Divergent Boundary Convergent Boundary (ex. Subduction zone) Transform Fault Boundary

Planet EarthSection 1  Boundary-border between two tectonic plates  Divergent boundary - place where two tectonic plates are moving apart.  New rock forms here MID-OCEANIC RIDGES RESULT FROM DIVERGENT BOUNDARIES

Planet EarthSection 1 MAGMA  Magma is liquid rock produced under Earth’s surface.  A rift valley is a narrow valley that forms where tectonic plates separate.

Planet EarthSection 1 PLATE BOUNDARIES, CONTINUED  Plates slide over each other at a convergent boundary.  The area where one plate slides over another is called a subduction zone. Subduction zones produce ocean trenches, mountains, and volcanoes. subduction: the process by which one lithospheric plate moves beneath another as a result of tectonic forces

Planet EarthSection 1 CONVERGENT BOUNDARIES

Planet EarthSection 1 VISUAL CONCEPT: CONVERGENT BOUNDARY

Planet EarthSection 1 VISUAL CONCEPT: SUBDUCTION ZONE

Planet EarthSection 1 PLATE BOUNDARIES, CONTINUED Subduction of ocean crust generates volcanoes.  Chains of volcanoes form on the upper plate in a subduction zone.  These volcanoes can form far inland from their associated oceanic trench. Islands may form where two oceanic plates meet.  Magma rising to the surface may form an island arc.

Planet EarthSection 1 PLATE BOUNDARIES, CONTINUED Colliding tectonic plates create mountains.  When two plates collide, mountains are formed at the boundary of the collision. Transform fault boundaries can crack Earth.  Causes earthquakes. FAULT: a break in a body of rock along which one block slides relative to another