I was wondering about the direction in which the pacific floor has been moving? in what direction has it been moving ? and what suggests this?
The floor of the Pacific Ocean is divided into several plates. The largest one, the Pacific Plate is moving north west relative to the plate that holds North America, and relative to hot spots coming up through the mantle from below the plates (they generate islands like Hawaii). On the surface of the earth, nothing can move along a straight line, instead the plates rotate around a point on the surface. The pacific plate rotates around a point south of Australia. Around Hawaii, the plate is moving at about 7 cm/year, or about as fast as finger mails grow.
The evidence for this motion is pretty convincing:
earthquakes: earthquakes occur on the boundaries of the plates as
they rub past each other. The motion observed during these earthquakes
agrees well with the expected motion.
absolute measurements: Thanks to the Global Positioning System
navigation system, we can now measure the location of any point on the
earth to within a few cm. The observed motions agree with expected plate
motions.
plate boundaries: where two plates meet there can be three types
of boundaries: transform faults where the plates slide past each other
(like the San Andreas fault); spreading centers where two plates are
moving away from each other (like the Juan de Fuca spreading center off the
Pacific NW and the mid-Atlantic Ridge; and subduction zones where one
plate dives into the earth under another plate (Aleutian Islands, Japan).
All the observed boundariies should agree with the expected motions - and
they do.
magnetism: new rock is added to the the plates at spreading
centers as they split apart. As this lave cools, it becomes magnetized,
much like a magnetic tape does in your tape recoder. When the magnetic
field of the earth changes, this change is recorded in the rocks. We can
read this record by sensing the changes in the magnetic field from ships,
and we see stripes of different magnetism parallel to the spreading
centers, as expected if the plates are splitting apart there.
sediments: in the deep ocean there is a very slow but continuous
rain of mud that slowly settles to the ocean bottom and forms layers of
sediment. Since the ocean floor is youngest near the spreading centers, we
would expect very little sediment there, and the layers should get thicker
the farther you get from a spreading center. This is observed, and the
age of the oldest (deepest) fossils in the sediment obtained by drilling in
the ocean floor gives us an idea of the age of the ocean floor at that
spot. Studies show that the ocean floor gets older as you get farther away
from spreading centers, and that the OLDEST ocean floor on the earth today
is only about 200 million years old. That may sound very old, but the
oldest FOSSILS are over 3 BILLION years old.
There is more evidence, and you can read about it in a good geology text book.
Dr. Fred Duennebier, Professor
Department of Geology and Geophysics
University of Hawaii, Honolulu, HI 96822