1. Hang on to Your Hat-The Earth's on the Move
What does the term "plate tectonics" mean? Why is the Earth so restless and what causes earthquakes, volcanoes, and the rise of mountains? How does the Earth's internal structure influence plate tectonics? How did the theories about continental drift and plate tectonics develop? What are the four major scientific developments that have spurred the formulation of the plate-tectonics theory? How does the ocean floor get mapped?
Follow the links below to discover more about plate tectonics and the recycling of the Earth's crust.
Consider This Before Answering the Questions
The maps at the beginning of Chapter 22 illustrate how the continents were once joined. Imagine one large continent that split apart-despite earthquakes, volcanoes, and other natural events, it's a good guess that this won't happen during our lifetimes, but it appears to have happened a long time ago.
To experience an exquisite and educational story of our dynamic world, visit http://pubs.usgs.gov/publications/text/dynamic.html and go to "This Dynamic Earth: The Story of Plate Tectonics." If you want to print this out, be warned that it's long. That's because there are so many beautiful photographs and other graphics, as well as side trips with additional information, but it's worth the time and paper. However, you needn't do a print-out to enjoy the journey, so let's begin by clicking on the "Preface" icon to get an overview, and then move forward to "Historical perspective," where we learn what the term "plate tectonics" means. Consider the maps to see the progression from Pangaea to the present day. How old is this theory and what has been its effect? Consider the questions of why the Earth is so restless and what causes earthquakes, volcanoes, and the rise of mountains. (By the way, as you move through this section, and each of the others, take advantage of the links within and the sidebars [icons] at the end of each section.) How old is the idea that continents have been moving over time? How do Abraham Ortelius and Alfred Lothar Wegener fit into this puzzle? Take a trip inside the Earth and describe its internal structure. What creates the Earth's magnetic field? How does the Earth's internal structure influence plate tectonics? How did polar dinosaurs wind up in Australia? Describe how the theories about continental drift and plate tectonics develop? What are the four major scientific developments that have spurred the formulation of the plate-tectonics theory? How does the ocean floor get mapped? What is magnetic striping (do check out that link!)? We hear a lot about recycling in our daily lives, but did you ever think about the oceanic crust being recycled? We'll talk more about earthquakes later, but what did you learn about them here? If you've watched anything about the ocean floor, surely you've heard about geothermal vents-go to the sidebar on "Exploring the deep ocean floor: Hot springs and strange creatures" to learn more about what's going on down there. Now, come back to the primary lesson at hand-understanding plate motions. What are the four types of plate boundaries? Describe them (be sure to look at the Ring of Fire). The next section, "'Hotspots': Mantle thermal plumes," poses the question, "How do the Hawaiian Islands and other volcanoes that form in the interior of plates fit into the plate-tectonics picture?" How would you answer that question? What idea did J. Tuzo Wilson come up with? Who first suspected that the Hawaiian Islands become younger as we move to the southeast, and why did they suspect it? Do take the long trail of the Hawaiian hotspot-what does the hotspot theory suggest about Loihi? After You Answer the Questions
As you might already have guessed, there are many unanswered questions: What drives the plates? Does tectonic activity take place on other planets? What went on before the break-up of Pangaea? What can you come up with as possible answers? This is all fascinating, but you might want to think about what this has to do with you-after all, the continents split apart long before any of us was around. The next section talks about "Plate tectonics and people"
http://pubs.usgs.gov/publications/text/tectonics.html First, it's noted that, together with other geologic processes, plate movements have created magnificent scenery, but have also caused terrible catastrophes. So, what are some natural hazards, and what is their effect on people? As you read this section and check out the maps, photos, and other graphics, you can begin to experience some of the danger of earthquakes. Everyone knows that there have been powerfully destructive earthquakes in California-as well as other parts of the world-but did you know about East Coast earthquakes?
2. Shake, Rattle, and Roll
You've just experienced an earthquake-it may be jarring, it may be rolling; hopefully you were not at the epicenter. But what caused this? Why is the seismic moment important? What are some practical ways to estimate the magnitude of an earthquake? What sources of information do seismologists use to make intensity ratings? Why would they do that?
To learn more about earthquakes and to answer these questions, follow links below.
Consider This Before Answering the Questions
Imagine lying in bed around 6:00 in the morning to be suddenly awakened by a shaking that goes on for several seconds, while you listen as pictures fall off walls, books and vases fall off shelves, and that wonderful carousel you loved so much crashes onto the floor. Then you rush to turn on the television to see buildings collapsed into rubble with people crushed inside. You're thankful that you lost just a few trinkets. This is one of those experiences where if you haven't been there you won't get the full impact, but let's take a stab at it.
Go to the University of Nevada-Reno web site, "About Earthquakes," at http://www.seismo.unr.edu/htdocs/abouteq.html . About halfway down that page you'll see a heading, "Lectures about Earthquakes." This is the tour we're taking, from "Plate Tectonics" to "Earth's Interior." The graphics are outstanding and the text is informative. Let's start by clicking on "Plate Tectonics," which they note is the cause of earthquakes. As you move through this site, jot down the terms and connect them in your mind to the pictures. What does the first pencil drawing show? What are the three main plate tectonic environments? How do they work? How does Nevada compare with California in terms of earthquake activity? Move on to the next lecture, "Seismic Waves," and describe the two types of deformation and how they affect the earthquake cycle. Explain seismic waves. What are seismographs and seismograms? How do they help us understand earthquakes? Go ahead and "listen" to the earthquakes, but understand it's not like "the real thing." How are earthquakes located? Move on to the next lecture, "Richter Magnitude"-this is what's used to describe the strength of an earthquake. The question is posed, "What is Richter Magnitude?" Start with the short answer, but do go on for the long one to get a more complete understanding. Why is the seismic moment important? What are some practical ways to estimate the magnitude of an earthquake? What is another measure that is presented? We will now move on to "Earthquake Effects in Kobe, Japan," and you can be happy you weren't there on January 17, 1995. As we look at the effects of earthquakes, what are the important factors? Why was the Loma Prieta earthquake less disastrous than the earthquake in Armenia that same year? What was it that happened in Kobe to make the 1/17/95 earthquake so disastrous? Describe the two classes of earthquake effects. What were the direct effects of the Kobe earthquake, and what were the secondary effects? How were lifelines affected? How did the fires begin? Explain the process of liquefaction and its effects. If you didn't look closely at all of the photographs in this section, go back to the beginning and check them out. What can they tell you even without the printed text? As you move on to the next section, "Earthquake Intensity," you'll see a different way to measure earthquake intensity, the Modified Mercalli Intensity Scale. How does this rate earthquake intensity? What information can it give that the Richter Scale doesn't? What sources of information do seismologists use to make intensity ratings? Why would they do that? After You Answer the Questions
Go to the last section the "Earth's Interior"
http://www.seismo.unr.edu/ftp/pub/louie/class/100/interior.html Of course, it's impossible at this point in time to journey to the center of the Earth, but scientists have techniques that provide information-describe what these techniques are and what they have learned about the structure of the Earth from inside to outer crust. How was the Earth's core discovered? What can you learn from exploring the Earth's mantle (what is the "mantle," anyway?)? What are the asthenosphere and the lithosphere? Describe the Earth's crust. How do the photos help you understand what the text is describing? How can learning about earthquakes and the Earth's interior apply to your own life (this doesn't have to be restricted to your science class)? Think about it.
