2Essential Questions What are the layers of the Earth? What is the lithosphere, asthenosphere, and mesosphere?What is an earthquake?What is the way to detect an earthquake?What are the ways to prepare for an earthquake?
4Bill Nye…..While watching the video complete your movie worksheet. This is to be put into your portfolio.24mins
5Layers of the Earth Transition region Oceanic crust Continental crust Lower mantleUpper mantleD“Outer coreInner core
6Layers of the Earth continued… Inner core:1.7% of the Earth's massdepth of 5,150-6,370 kilometersunattached to the mantle, suspended in the molten outer coreis solid iron-nickel alloyis hotter than the outer core, may have a temperature up to about 13,000°F (7,200°C = 7,500 K), but the intense pressure keeps it solidOuter core:30.8% of Earth's massdepth of 2,890-5,150 kilometersis composed of an iron-nickel alloyis a hot, electrically conducting liquidInner core: It is believed to have solidified as a result of pressure-freezing which occurs to most liquids when temperature decreases or pressure increases. ), which is hotter than the surface of the SunOuter core: This conductive layer combines with Earth's rotation to create a dynamo effect that maintains a system of electrical currents known as the Earth's magnetic field. This layer is not as dense as pure molten iron, which indicates the presence of lighter elements. Scientists suspect that about 10% of the layer is composed of sulfur and/or oxygen because these elements are abundant in the cosmos and dissolve readily in molten iron.
7Layers of the Earth continued… 3% of Earth's massdepth of 2,700-2,890 kilometersAlthough it is often identified as part of the lower mantle, seismic discontinuities suggest the D" layer might differ chemically from the lower mantle lying above it.Lower mantle:49.2% of Earth's massdepth of 650-2,890 kilometersis probably composed mainly of silicon, magnesium, and oxygen. It probably also contains some iron, calcium, and aluminum.Transition region:7.5% of Earth's massdepth of kilometersis dense when cold because of the garnet. It is buoyant when hot because these minerals melt easily to form basalt which can then rise through the upper layers as magma.D": Scientists theorize that the material either dissolved in the core, or was able to sink through the mantle but not into the core because of its density.
8Layers of the Earth continued… Upper mantle:10.3% of Earth's massdepth of kilometersOceanic crust:0.099% of Earth's massdepth of 0-10 kilometersthe majority of the Earth's crust was made through volcanic activity.Continental crust:0.374% of Earth's massdepth of 0-50 kilometersis the outer part of the Earth composed essentially of crystalline rocks.Oceanic crust: The oceanic ridge system, a 40,000-kilometer (25,000 mile) network of volcanoes, generates new oceanic crust at the rate of 17 km3 per year, covering the ocean floor with basalt
9Time to pause…. In your portfolio answer the following question: We often hear the Earth referred to as solid. With the information you now have explain if this is true or false.
10What is the lithosphere, asthenosphere, and mesosphere?
11Earth’s Structural Zones The Earth is divided into 5 structural zones:LithosphereAsthenosphereMesosphereOuter CoreInner CoreWe have already reviewed the outer and inner core.
12Lithosphere It's very stiff, and fractures if you push too hard The lithosphere is part of the crust and the upper mantle.The prefix "lithos" is Greek for "stone" or "rock."This layer is solid and the most rigid of the other layers.It is about 15 to 300 kilometers thick.
13Asthenosphere It's hot and flows like molasses The asthenosphere lies below the lithosphere.Its prefix "asthenes" is Greek for the word "weak.“Keep in mind; it is not as weak as a brittle piece of wood. However, it is weaker than the other layers.This layer is about 200 kilometers thickIt contains hotter, softer rock that flows like lava.
14MesosphereThe mesosphere or "middle layer" is found at the lower part of the mantle.Scientists believe it is solid rock.
15So how do scientists know this? Geophysical surveys: seismic, gravity, magnetics, electrical, geodesyAcquisition: land, air, sea and satelliteGeological surveys: fieldwork, boreholes, minesWhat are seismic waves?When a sudden break or shift occurs in the earth's crust, the energy radiates out as seismic waves.There are 2 categories of seismic waves:Body wavesSurface wavesjust as the energy from a disturbance in a body of water radiates out in wave form.If we can’t go to the centre of the Earth (except in fictional movies!) how do we know what the internal structure of the Earth is like?We need to use geophysical imaging techniques to model what is going on below our feet.For example, when there is an earthquake it sends out seismic waves (shock waves) through the Earth. Seismologists can measure the time it takes for these waves to reach seismic monitoring stations set up around the globe. (The machine that measures seismic waves is called a seismometer).The different layers in the earth have been inferred using the time of travel of refracted and reflected (bent backward angularly) seismic waves created by the earthquakes (see left diagram). That is, changes in the seismic velocity occur as the waves pass through different materials. Measuring these changes tell seismologists how many layers there are and the thickness and physical properties of each layer.We need not wait for earthquakes to occur, on a local scale on land (cheap but slow methods) and at sea (more expensive but quicker) explosions can be set to cause shock waves to pass through the crust (simulating an earthquake) that can be measured in the same way.Other geophysical methods, for example measuring different gravity, magnetic and electrical anomalies by air and (or) satellite can help to reconstruct shallow crustal features.We can also go and examine rocks at and near the surface of the crust, through fieldwork, drilling boreholes and mining.
17Bill Nye - EarthquakesComplete the Question sheet provided.24mins
18Body waves Move through the inner part of the earth There are 2 types of body wavesPrimary waves, also called P waves or compressional wavesP waves arrive first at any surface locationcan travel through solid, liquid and gasare waves that have the same direction of vibration along their direction of travel, which means that the vibration of the medium (particle) is in the same direction or opposite direction as the motion of the waveAs they travel through rock, the waves move tiny rock particles back and forth -- pushing them apart and then back togetherSecondary waves, also called S waves or shear wavesAs these waves move, they displace rock particles outwardS waves don't move straight through the earthonly travel through solid materialthe ground is displaced perpendicularly to the moves alternately to one side and then the otherP waves - travel about 1 to 5 miles per second (1.6 to 8 kps), depending on the material they're moving through
19Surface Waves sometimes called long waves, or simply L wave are responsible for most of the damage associated with earthquakes, because they cause the most intense vibrationsstem from body waves that reach the surfaceare something like the waves in a body of water -- they move the surface of the earth up and downL waves are the slowest moving of all waves
21Both P and S waves refract or reflect at points where layers of differing physical properties meet. They also reduce speed when moving through hotter material. These changes in direction and velocity are the means of locating discontinuities.Seismic discontinuities (a surface at which velocities of seismic waves change abruptly) aid in distinguishing divisions of the Earth into inner core, outer core, D", lower mantle, transition region, upper mantle, and crust (oceanic and continental).
22Earthquakes Did you know… According to the United States Geological Survey, more than three million earthquakes occur every year. That's about 8,000 a day, or one every 11 seconds!
24Detection Detecting an earthquake is much easier than predicting one. a powerful earthquake can be felt by people in the area, and the damage it causes can be seen.A machines, known as seismometers, or seismographs, is usedthey can record the movements automatically,they work on a simple principle; that a heavy weight suspended on a wire will remain steady as the vibrations pass, whilst the frame holding it will be vibrated.
25Reading a SeismogramWhen you look at a seismogram, there will be wiggly lines all across it. These are all the seismic waves that the seismograph has recorded.Most of these waves were so small that nobody felt them.
26Reading a Seismogram continued The P wave will be the first wiggle that is bigger than the rest of the little ones (the microseisms).Because P waves are the fastest seismic waves, they will usually be the first ones that your seismograph records.The next set of seismic waves on your seismogram will be the S waves.These are usually bigger than the P waves.If there aren't any S waves marked on your seismogram, it probably means the earthquake happened on the other side of the planet. S waves can't travel through the liquid layers of the earth so these waves never made it to your seismograph.The surface waves are the other, often larger, waves marked on the seismogram.They have a lower frequency.Surface waves travel a little slower than S waves.
27Finding the EpicenterMeasure the distance between the first P wave and the first S wave. In this case, the first P and S waves are 24 seconds apart.Find the point for 24 seconds on the left side of the chart below and mark that point. According to the chart, this earthquake's epicenter was 215 kilometers away.Measure the amplitude of the strongest wave. The amplitude is the height (on paper) of the strongest wave. On this seismogram, the amplitude is 23 millimeters. Find 23 millimeters on the right side of the chart and mark that point.Place a ruler (or straight edge) on the chart between the points you marked for the distance to the epicenter and the amplitude. The point where your ruler crosses the middle line on the chart marks the magnitude (strength) of the earthquake. This earthquake had a magnitude of 5.0.
28The Richter ScaleThe Richter Scale is the best known scale for measuring the magnitude of earthquakes.The energy released by an earthquake increases by a factor of 30 for every unit increase in the Richter scale.An earthquake that measures 4.0 on the Richter scale is 10 times larger than one that measures 3.0
29No. of earthquakes per year Richter scale no.No. of earthquakes per yearTypical effects of this magnitude< 3.4Detected only by seismometers30 000Just about noticeable indoors4 800Most people notice them, windows rattle.1400Everyone notices them, dishes may break, open doors swing.500Slight damage to buildings, plaster cracks, bricks fall.6.2 6.9100Much damage to buildings: chimneys fall, houses move on foundations.15Serious damage: bridges twist, walls fracture, buildings may collapse.4Great damage, most buildings collapse.> 8.0One every 5 to 10 yearsTotal damage, surface waves seen, objects thrown in the air.