Shifting Continents: A Case Study in Scientific Revision Even though you may not

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Shifting Continents: A Case Study in Scientific Revision

Even though you may not feel it, the earth is moving beneath your feet. The tectonic plates have been moving for millennia and have caused volcanic eruptions, earthquakes, tsunamis, and continents to change shape. This must take an immense amount of energy. Where does it come from? The heat from the earth’s inner core drives the movement of the plates. This heat energy is left over from the formation of the earth and some comes from the decay of naturally occurring radioactive materials. Today a lot is understood about the geologic processes. However not too long ago it was a mystery how mountains were formed and why earthquakes and volcanic eruptions happened. Many hypotheses were put forward that eventually were proven false. This is a normal part of the scientific process. Whenever new discoveries force scientists to reconsider their hypotheses, theories, and data, they do just that. Therefore, people think of science as a collection of concepts that are always being revised. The shift from the theory of continental drift proposed by Alfred Wegner in 1912 to modern plate tectonic theory is an example of this constant revision of scientific understanding as experiments generate new information.

For additional information on plate tectonics and Alfred Wegner check out this KU Science Center link:

https://kucampus.kaplan.edu/MyStudies/AcademicSupportCenter/ScienceCenter/ScienceResources1/Earth%20Science/PlateTectonics.aspx

Using what you learned about plate tectonics, Alfred Wegener, and the basics of scientific investigation from the previous units discuss the following:

Navigate to the following site: U.S. Geological Survey Earthquake Map. (2016). Retrieved fromhttp://earthquake.usgs.gov/earthquakes/map/Zoom out to see all the earthquakes that have happened worldwide today. List the most recent earthquake and its magnitude. How many earthquakes have happened in the last day? Why do so many occur near plate boundaries (red lines on map)?

Look at the following map of the world where triangles represent active volcanoes:NOVA: Teacher's Images. (2015). Retrieved fromhttp://www-tc.pbs.org/wgbh/nova/education/activities/images/2515_vesuvius_map2.gif Why do so many occur near plate boundaries (yellow lines on map)?

Pick one active volcano or earthquake from around the globe or a historical geological event and explain the following

What plates or hot spots it is associated with.

How the plates or hot spots are causing/caused the volcanic event/earthquake.

How energy from deep within the earth is/was transferred to and released during the volcanic event/earthquake.

If Alfred Wegener were alive today, and had access to the technology and data that exists today, share a form of evidence that he could have added to his hypothesis or would have changed his hypothesis. Try to share a different form of evidence from those shared by your classmates and/or add to their posts by describing how the evidence is collected, how the technology works to collect the data, or how this technology/evidence has been used in other applications.

Explanation / Answer

Looking at the map of the Last Earthquakes provided by the U.S. Geological Survey, on ots Web Site, it can be identified the most recent earthquake it was located at 5 km of Summit Park, Utah and its magnitude was 3.3 .

In the last day it have happened 31 earthquakes around the world.

As we read above, according to the theory of continental drift proposed by Alfred Wegner in 1912 to modern plate tectonic theory, the Earth's surface is made up of different plates. These plates are in constant movement. Some move away from each other, but others push or slide against each other.

When plates move away the molten magma to from the earth's core comes up. When this magma cools it forms rock (igneous). Over time and as the rocks move further away, the rock gets bigger and bigger until it forms a volcano, for example.

But, when plates push or slide against each other then pressure builds. This pressure builds and builds constantly until there is a sudden jolt. This jolt is the earthquake and that is why earthquakes occur along plate boundaries. About 90%of the world's earthquakes and 81% of the world's largest earthquakes occur along the Ring of Fire. The next most seismically active region (5–6% of earthquakes and 17% of the world's largest earthquakes) is the Alpide belt, which extends from Java to the northern Atlantic Ocean via the Himalayas and southern Europe

About why do so many volcanoes occur near plate boundaries (yellow lines on map), remember that the lines that surround the Pacific Ocean are the boundaies of the Pacific Ring of Fire is a major area in the basin of the Pacific Ocean where a large number of earthquakes and volcanic eruptions occur. In a 40,000 km horseshoe shape, it is associated with a nearly continuous series of oceanic trenches, volcanic arcs, and volcanic belts and/or plate movements. It has 452 volcanoes (more than 75% of the world's active and dormant volcanoes).                    Earth's volcanoes occur because its crust is broken into 17 major, rigid tectonic plates that float on a hotter, softer layer in its mantle.Therefore, on Earth, volcanoes are generally found where tectonic plates are diverging or converging, and most are found underwater. For example, a mid-oceanic ridge, such as the Mid-Atlantic Ridge, has volcanoes caused by divergent tectonic plates whereas the Pacific Ring of Fire has volcanoes caused by convergent tectonic plates, as we explained already above.

It was picked the event on March 11, 2011, a magnitude-9 earthquake shooking northeastern Japan, unleashing a savage tsunami.

The plates associated with this event were the Pacific Plate and the plate beneath northern Honsu.

The Pacific plate, which moves at a rate of 8 to 9 cm per year, dips under Honshu's underlying plate building large amounts of elastic energy. This motion pushes the upper plate down until the accumulated stress causes a seismic slip-rupture event. The break caused the sea floor to rise by several metres. A quake of this magnitude usually has a rupture length of at least 500 km and generally requires a long, relatively straight fault surface. Because the plate boundary and subduction zone in the area of the Honshu rupture is not very straight, it is unusual for the magnitude of its earthquake to exceed 8.5 Mw.

The surface energy of the seismic waves from the earthquake was calculated to be at 1.9×1017 joules, which is nearly double that of the 9.1 Mw 2004 Indian Ocean earthquake and tsunami that killed 230,000 people. If harnessed, the seismic energy from this earthquake would power a city the size of Los Angeles for an entire year.The seismic moment (M0), which represents a physical size for the event, was calculated by the USGS at 3.9×1022 joules, slightly less than the 2004 Indian Ocean quake. Japan's National Research Institute for Earth Science and Disaster Prevention (NIED) calculated a peak ground acceleration of 2.99 g (29.33 m/s2). The largest individual recording in Japan was 2.7 g, in Miyagi Prefecture, 75 km from the epicentre; the highest reading in the Tokyo metropolitan area was 0.16 g.

It is now possible, using space technology, to directly measure the relative movement between plates.
This is done by periodically establishing the exact locations and, therefore, the distance between two observation stations located on the opposite sides of a plate edge. Two of the methods used to perform this calculation are Long Baseline Interferometry (VLBI) and a satellite positioning technique using the Global Positioning System (GPS). In the very long basal interfermetry system, large radio telescopes are used to record distant quasars (almost stellar objects). Quasars are thousands of millions of light years from Earth, so they act as stationary landmarks. The millisecond differences in the arrival times of the same signal to different observatories with direction to the Earth provide a way to establish the precise distance between the receivers. The completion of a typical study may take one day and requires two widely spaced radio telescopes to observe perhaps a dozen quasars, 5 to 10 times each. This scheme provides an estimate of the distance between these observatories with an accuracy of about 2 centimeters. Repeating this experiment later, researchers can establish the relative movement of these places. This method has been particularly useful for establishing the large-scale movements of the plates, such as the separation that is taking place between the United States and Europe.
You may be familiar with the Global Positioning System, which is part of the navigation system used in cars to locate your own position and give directions to another location. Numerous satellites are used in the Global Positioning System instead of an extragalactic source to accurately measure the location of a particular point on the Earth's surface. Using two widely separated GPS receivers, the signals obtained by these instruments can be used to calculate their relative positions with considerable accuracy. It has been demonstrated that the techniques in which GPS receivers are used are useful for establishing small-scale movements of the crust as those occurring along faults in tectonically active regions.
The data obtained from these and other techniques confirm the fact that actual plate movement has been detected. Calculations show that Hawaii moves northwest and approaches Japan at 8.3 centimeters a year. One point in Maryland is moving away from another in England at a rate of about 1.7 centimeters per year (a velocity close to the velocity of expansion of 2.3 centimeters per year that was established from the paleomagnetic data).

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