TOPIC 3 and EXTENDED B OBJECTIVES
THE DYNAMIC CRUST
1. Identify 3 types of evidence that suggests there was movement of the Earth's crust in the past.
2E. Name 2 types of earthquake waves.
3E. Using the Earth Science Reference Tables (ESRT), compare the speed of P and S waves
P-waves are faster than S-waves.
4E. Using the arrival times of P and S waves and the ESRT, determine the epicenter distance of an earthquake.
The chart that students need for this objective is on page 11 of the ESRT.*Page 11 ESRT* Students also need to understand some vocabulary.
Focus: This is the location in the Earth where the earthquake actual happens.5E. a. Define origin time.
This is the time that the earthquake started.
b. Using the ESRT and given the epicenter distance and the arrival time of the P wave determine the origin time of an earthquake.
To find the origin time students must subtract the P-wave travel time from the arrival time for the P-wave. P-wave travel time can be determine by applying the distance to the epicenter to the P + S-wave chart on page 11 of the ESRT.
6E. Given the P and S wave graph in the ESRT and 3 seismograms, determine the location of an earthquake epicenter.
Students use the seismograms to determine the distance to the epicenter from three locations. They then draw circles on a map, in which the radius of the circle is equal to the distance to the epicenter for that location. Where the three circles intersect is the location of the epicenter.
7. Describe how changes in density of the Earth's interior effect the speed of earthquake waves.
The greater the density the faster earthquake waves travel.
8. Describe evidence from seismic data that suggests the Earth is not a solid body.
S-waves do not travel through the outer core. Since S-waves can only travel through solids this implies that the outer core is not solid.
9. Compare the Richter and Mercalli scales for measuring the strength of Earthquakes.
10. Describe the possibility of an earthquake occurring in our area.
Earthquakes happen along faults in the Earth's crust. There are faults in New York, which means earthquakes are possible in this State. The faults in New York however, are not active. This makes the probability of an earthquake low.
11E. Using the Inferred Properties of the Earth's Interior chart in the ESRT, describe the changes in density, temperature, and pressure as you move toward the center of the Earth.
The chart is on page 10 of the ESRT. *Page 10 ESRT* The charts show that as you move towards the center of the Earth density, temperature, and pressure increases.
12E. Using the ESRT, identify the regions of the Earth's interior and determine the depth at which they occur.
This information is on page 10 of the ESRT. *Page 10 ESRT* From the surface of the Earth to the center the major division of the earth are:
13E. a. State the inferred composition of the Earth's core.
Page 10 of the ESRT has this information. *Page 10 ESRT*The core is thought to be made of iron and nickel.
b. Give supporting evidence.
This inference is based on seismic data and the composition of meteorites.
14E. Describe evidence that supports the theory of continental drift.
What originally started the investigation that lead to the theory of continental drift was the jigsaw puzzle fit of the continents. Comparisons were made between the East Coast of North America and the West Coast of Europe. Similarities were also examined between the East Coast of South America and the West Coast of Africa. They found matches in the mineral, fossil, climate, and geologic records between these coasts.
15E. Describe convection cells within the asthenosphere and how they move the lithospheric plates.
Convection currents are caused by differences in density in liquids or gasses. The differences in densities are caused by differences in temperature. It is felt that convection currents in the asthenosphere cause the less dense lithosphere to move. The movement is similar to how a piece of wood is moved by a current in the water it is floating in.
16. Define plate tectonics.
Plate tectonics is a theory which divides the Earth's surface, or lithosphere, in to large sections called plates. Because the these plates are less dense than the material below, asthenosphere, they basically float. Convection currents in the asthenosphere cause the plates to move.
17E. Describe evidence that supports the theory of plate tectonics.
Continental drift and sea floor spreading support the theory plate tectonics. So does the fact that crustal activity is found in specific locations. Since convection currents are a key component to the theory there should be differences in temperature. Temperature differences have been detected.
18. Compare the location of earthquakes, volcanoes and mountains to the position of plate boundaries.
All of these crustal activities happen in the same locations, which is at plate boundaries. Page 5 of the ESRT is a map that shows the plate boundaries and motions. *Page 5 ESRT*
19. Describe the movement that occurs along 3 types of plate boundaries:
20E. Compare the thickness, composition and age of the continental crust and oceanic crust.
21. On a map of the world, identify locations of frequent crustal activity.
