I.
The Theory of Plate Tectonics says that the Earth’s crust and part of the upper
mantle (the lithosphere) are broken up into plates, which sit on top of the
upper mantle, which is plastic (the asthenosphere). This plastic part of the
mantle slowly moves over time causing the plates to move. The edges of these
plates are geologically active (volcanoes, earthquakes, mountain building)
while the interior of the plates is fairly quiet geologically.http://pubs.usgs.gov/publications/text/slabs.html
II.
Evidence to support the theory of plate tectonics:
1.
The
continents look like they fit together like the pieces of a jigsaw puzzle (this
includes being able to match their coastlines, rock types and ages, and fossil
distribution).
http://kids.earth.nasa.gov/archive/pangaea/Pangaea_game.html
http://pubs.usgs.gov/publications/text/continents.html
2.
Scientists
have discovered huge underwater mountain ranges along the floor of the world’s
oceans such as the mid-Atlantic ridge. These mountains are sites of tremendous
volcanic activity.
http://pubs.usgs.gov/publications/text/baseball.html
a) These mid-ocean ridges are
the site of sea-floor spreading. The idea that movement (convection cells) in
the asthenosphere causes the plates to move apart at these mid-ocean ridges.
New crust is formed as lava flows to the surface and hardens.
1.
The
layer of sea floor sediments is thinnest at the mid-ocean ridges and gets
thicker as you move away in both directions.
2.
Core
samples of sea-floor rock shows that the youngest rock is found at the
mid-ocean ridges and gets older as you move away. The oldest rocks on the floor
of the Atlantic ocean are only 200 million years old.
3.
There
is a pattern of magnetic strips that is the same on both sides of these
mid-ocean ridges.
http://pubs.usgs.gov/publications/text/magnetic.html
b)Mapping of earthquake and volcanic activity.
Earthquakes and volcanoes are not distributed evenly over the surface of the
Earth. They are concentrated in particular areas. These areas are the
boundaries between the tectonic plates. We live at one of these boundaries, the
San Andreas Fault, where the Pacific plate and The North American plate meet.
http://pubs.usgs.gov/publications/text/zones.html
c) Measurement of the plate
movement using satellites and lasers. These measurements show that the plates
are moving as much as an inch a year.