Warm Up 10/21(22). When an earthquake occurs, energy radiates in all directions from its source, which is called the ____. a. fault c. seismic center b. epicenter d. focus The hypothesis that explains the release of energy during an earthquake is called the ____.
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Warm Up 10/21(22) • When an earthquake occurs, energy radiates in all directions from its source, which is called the ____. a. fault c. seismic center b. epicenter d. focus • The hypothesis that explains the release of energy during an earthquake is called the ____. a. moment magnitude hypothesis c. Richter hypothesis b. elastic rebound hypothesis d. vibration hypothesis • Most earthquakes are produced by the rapid release of which kind of energy stored in rock subjected to great forces? a. thermal c. chemical b. elastic d. Mechanical 1. d, 2. b, 3. b
Earth’s Layered Structure Chapter 8, Section 4
Layers Defined by Composition • If Earth were made up of the same materials throughout its interior, seismic waves would travel in straight lines at constant speeds • Seismic waves reaching seismographs located farther from an earthquake travel at faster average speeds, due to increased pressure at depth • Earth’s interior consists of three major zones defined by its chemical composition – the crust, mantle, and core
The Crust • Crust – thin, rocky, outer layer of Earth; divided into oceanic and continental crust • The oceanic crust is roughly 7 kilometers thick and composed of the igneous rocks basalt and gabbro • The continental crust is 8-75 kilometers thick (avg. 40 km) and consists mostly of the granitic rock granodiorite • The rocks of the oceanic crust are younger then the rocks of the continental crust
Mantle and Core • Mantle – a solid, rocky shell that extends to a depth of 2890 km • Over 82% of Earth’s mass is contained in the mantle • The boundary between the crust and mantle represents a chemical composition change • Core – a sphere composed of an iron-nickel alloy
Concept Check • What is the composition of the core? • An iron-nickel alloy
Layers Defined by Physical Properties • Earth’s interior has a gradual increase in temperature, pressure, and density with depth • Depending on the physical environment (temperature and pressure), a material may behave like a brittle solid, a putty, or a liquid • Earth can be divided into layers based on physical properties – the lithosphere, asthenosphere, outer core, and inner core.
Lithosphere and Asthenosphere • Lithosphere – relatively cool, rigid shell consisting of the crust and upper most mantle • Averages about 100 kilometers in thickness • Asthenosphere – soft, comparatively weak layer beneath the lithosphere • The rocks within the asthenosphere are close enough to their melting points that they are easily deformed
Lower Mantle • From a depth of 660 km down to near the base of the mantle • More rigid layer that is still prone to gradual flow • At the bottom of the mantle, rocks behave more like those in the asthenosphere
Inner and Outer Core • The core, which is composed of an iron-nickel alloy, is divided into two regions with different physical properties • Outer Core – liquid layer 2260 km thick, flow produces Earth’s magnetic field • Inner Core – sphere with a radius of 1220 km, compressed into a solid state by immense pressure
Concept Check • Why is the inner core solid? • It is under extreme pressure and is compressed into a solid as a result
Discovering Earth’s Layers • Moho – boundary separating the crust from the mantle where the velocity of seismic waves abruptly increases • Seismic waves from even small earthquakes can travel around the world • The outer core causes P waves that travel through it to arrive several minutes after expected and are bent by 100o away from the earthquake (shadow zone) • It was further shown that S waves do not travel through the outer core, making geologists conclude that the outer core is composed of a liquid
Concept Check • What is the Moho? • The boundary between the crust and the mantle
Discovering Earth’s Composition • Early seismic data and drilling technology indicate that the continental crust is mostly made of lighter, granitic rocks • The crust of the ocean floor has a baslatic composition • The composition of the mantle and core is known from more indirect data • Scientists use lava and meteorites to infer the composition of the mantle and core • Earth’s core is thought to be mainly dense iron and nickel, similar to metallic meteorites. The surrounding mantle is believed to be composed of rocks similar to stony meteorites
Assignment • Read Chapter 8, Section 4 (pg. 233-237) • Do 8.4 Assessment #1-6 (pg. 237)