Make your own free website on Tripod.com
Project on plate tectonics
Home
Page Title

INFO ON PLATE TECTONICS
 
In the early 1960s, the emergence of the theory of plate tectonics started a revolution in the earth sciences. Since then, scientists have verified and refined this theory, and now have a much better understanding of how our planet has been shaped by plate-tectonic processes. We now know that, directly or indirectly, plate tectonics influences nearly all geologic processes, past and present. Indeed, the notion that the entire Earth's surface is continually shifting has profoundly changed the way we view our world.

There are four types of plate boundaries:

  • Divergent boundaries -- where new crust is generated as the plates pull away from each other.
  • Convergent boundaries -- where crust is destroyed as one plate dives under another.
  • Transform boundaries -- where crust is neither produced nor destroyed as the plates slide horizontally past each other.
  • Plate boundary zones -- broad belts in which boundaries are not well defined and the effects of plate interaction are unclear.

Rates of motion

We can measure how fast tectonic plates are moving today, but how do scientists know what the rates of plate movement have been over geologic time? The oceans hold one of the key pieces to the puzzle. Because the ocean-floor magnetic striping records the flip-flops in the Earth's magnetic field, scientists, knowing the approximate duration of the reversal, can calculate the average rate of plate movement during a given time span. These average rates of plate separations can range widely. The Arctic Ridge has the slowest rate (less than 2.5 cm/yr), and the East Pacific Rise near Easter Island, in the South Pacific about 3,400 km west of Chile, has the fastest rate (more than 15 cm/yr).

the liquid comming
fig13thumb.jpg
from the core of the earth..which is magma

this ladies and gentalmen
fig22swatch.jpg
is the ring of fire..

Enter main content here

this is the plates
fig2-1globethumb.jpg
in the past as they appear

these are two plates
fig16.jpg
diverging from one another

this picute is showin the subduction
fig21oceancont.jpg
of the plates taken place at the lithosphere and the continental crust

Divergent boundaries Divergent boundaries occur along spreading centers where plates are moving apart and new crust is created by magma pushing up from the mantle. Picture two giant conveyor belts, facing each other but slowly moving in opposite directions as they transport newly formed oceanic crust away from the ridge crest. The volcanic country of Iceland, which straddles the Mid-Atlantic Ridge, offers scientists a natural laboratory for studying on land the processes also occurring along the submerged parts of a spreading ridge. Iceland is splitting along the spreading center between the North American and Eurasian Plates, as North America moves westward relative to Eurasia. Convergent boundaries The size of the Earth has not changed significantly during the past 600 million years, and very likely not since shortly after its formation 4.6 billion years ago. The Earth's unchanging size implies that the crust must be destroyed at about the same rate as it is being created, as Harry Hess surmised. Such destruction (recycling) of crust takes place along convergent boundaries where plates are moving toward each other, and sometimes one plate sinks (is subducted) under another. The location where sinking of a plate occurs is called a subduction zone. The type of convergence -- called by some a very slow "collision" -- that takes place between plates depends on the kind of lithosphere involved. Convergence can occur between an oceanic and a largely continental plate, or between two largely oceanic plates, or between two largely continental plates.

project on plate tectonics.

PLATE TECTONICS.