Fossil Evidence

1. Fossil Evidence

2. “Tectonic Plates”

3. The Theory of Plate Tectonicsgains credibility due in part to the observation that most geologic activity (earthquakes and volcanic activity) is concentrated along oceanic trenches and submarine mountain ranges. This suggests “movement” Activity and unique features in these newly discovered regions serve as indirect evidence of plate tectonics.

4. Nowadays, technology allows us to directly observe and measure these movements. Current plate movement can be tracked directly by means of ground-based or space-based geodetic measurements; geodesy is the science of the size and shape of the Earth. Ground-based measurements are taken with conventional but very precise ground-surveying techniques, using laser-electronic instruments. However, because plate motions are global in scale, they are best measured by satellite-based methods. The late 1970s witnessed the rapid growth of space geodesy, a term applied to space-based techniques for taking precise, repeated measurements of carefully chosen points on the Earth's surface separated by hundreds to thousands of kilometers. The three most commonly used space-geodetic techniques -- very long baseline interferometry (VLBI), satellite laser ranging (SLR), and the Global Positioning System (GPS) -- are based on technologies developed for military and aerospace research, notably radio astronomy and satellite tracking.

5. The discovery of the Mid- Atlantic Ridge explains a lot!

8. Areas where plates interact are termed Plate Boundaries There are 3 main types of boundaries, classified by the type of movement occuring. For example, some plates move toward one another, while some move away. Some even slide past one another.

9. Transform boundaries are where • plates slip past one another in • opposite directions. Crust is neither produced nor destroyed

10. When two plates get “hung up” when grinding past each other and later release their movement all at one time, Earthquakes may occur. Fractures zones in the Earth’s crust called Faults also occur along these transform boundaries. Aerial view of the San Andreas fault slicing through the Carrizo Plain in the Temblor Range east of the city of San Luis Obispo. (Photograph by Robert E. Wallace, USGS.)

11. 2. Divergent boundaries occur where plates move apart (diverge). On continental crust, this forms aRift Valley On oceanic crust, this forms anOcean Ridge

12. 3. Convergent boundaries occur in areas where two plates come together (converge) What happens during this collision depends on what types of crusts are involved Think “Density”

13. The least dense of the two plates literally comes out “on top”. The denser dives beneath. This is called “subduction”, and places where this occurs are called Subduction Zones

14. Although both crusts are similar material the denser of the two subducts back into the mantle. This creates a deep sea Trench

15. The denser oceanic crust is always subducted when colliding with continental crust. This also creates a Trench usually near a shore line. Mountain ranges also frequently develop on the coast

16. There is no subduction because neither is dense enough to sink. Instead they “buckle” or rise, squeezing crust upward into mountain ranges.

17. Sometimes, constructive and destructive forces occur at places that are not near plate boundaries, but rather in the middle of plates. The great majority of the world's earthquakes and active volcanoes occur near the boundaries of the Earth's shifting plates. Why then are the Hawaiian volcanoes located near the middle of the Pacific Plate, more than 2,000 miles from the nearest plate boundary? In 1963, J. Tuzo Wilson, a Canadian geophysicist, provided an ingenious explanation within the framework of plate tectonics by proposing the "Hot Spot" hypothesis. Wilson's hypothesis has come to be accepted widely, because it agrees well with much of the scientific data on the Pacific Ocean in general, and the Hawaiian Islands in particular. According to Wilson, the distinctive linear shape of the Hawaiian-Emperor Chain reflects the progressive movement of the Pacific Plate over a deep immobile hot spot. This hot spot partly melts the region just below the overriding Pacific Plate, producing small, isolated blobs of magma. Less dense than the surrounding solid rock, the magma rises buoyantly through structurally weak zones and ultimately erupts as lava onto the ocean floor to form volcanoes. By The Way.. These events gave scientists of the time further evidence that plates are in fact moving!

18. Hot spots “burn” a chain of volcanoes on to the moving crust above:

19. How and why do the Earth’s tectonic plates move? Convection Currents Convection is how heat is transferred through a fluid (a fluid is either a solid or a liquid) What part of the Earth’s interior is liquid?

20. In this case, the heat source is the Core. The molten rock that is closest to the core becomes hotter and therefore less dense. Because less dense materials rise and denser material sink a pattern forms……. Hot liquids are less dense than cold and will rise. In the earth’s deep mantle and outer core, the magma that is closer to the extremely hot inner core rises because it’s less dense and then pushes the cooler magma that is further from the intense heat down. When the cooler magma is pushed down, it is heated more and rises. The somewhat less hot magma is more dense and so sinks. This motion is convection currents and is what causes the plates to move that are riding on the surface of all of this.

21. Even though each plate weighs trillions of tons, the energy in the center of the Earth is so great that it is able to move them around easily!

22. Crust is both created and destroyed because of these movements. It moves like a conveyor belt or an escalator to be continuously recycled at plate boundaries.

23. If the Earth’s interior were to cool, convection currents would cease. Therefore plates would stand still. There would be no more volcanoes, earthquakes, tsunamis, mountain building and so on.