Transcript Session 3 Powerpoint

Tectonic plate = Lithosphere
How plate tectonics got
figured out
-Study of continents
(Theory of continental drift;
Wegener)
-Study of oceans
(Theory of continental drift
becomes part of larger Theory of
plate tectonics)
CONTINENTAL DRIFT
The continents have moved around the globe over time.
Evidence for continental drift:
The shapes of continents match
The rocks match
The plants match
The ice matches
Yet, the current positions don’t match
They were all together about 250
Million years ago (I’ll call it Pangea,
meaning “all the Earth” in Greek)
Alfred Lothar Wegener (1880-1930)
What makes a good scientific
theory?
Scientific Theory - A hypothesis or group of hypotheses
that: 1) Explains scientific observations; 2) Is tested
with repeated experiments and observations and found
always to work; and 3) Is accepted by the scientific
community.
A good scientific theory:
1) Logical consistency
2) Agrees with the data
3) Verifiable causes that explain and predict
4) Advanced comparisons (simplicity, tradeoff of
generality and specificity, distinction between non-fatal
difficulties and fatal difficulties)
1950s: The bathymetry (topography) of the ocean floor.
Bruce Heezen
Marie Tharp
Harry Hess
Proponent of sea-floor spreading. Used data collected
during WW II in Atlantic Ocean.
1963
Fred Vine and Drummand Matthews
In 1967, W. Jason Morgan proposed that
the Earth's surface consists of 12 rigid
plates that move relative to each other.
Two months later, in 1968, Xavier Le
Pichon published a complete model
based on 6 major plates with their
relative motions.
Common Misconception: The convecting mantle is solid
(not liquid, despite the boiling water analogy)
Clarification: The plates can grow or shrink, by the
addition of oceanic lithosphere at a mid-ocean ridge or
the removal of ocean lithosphere at a subduction zone
Clarification: Although the continental lithosphere does not go
away, the pieces of the continents have arranged themselves
differently over time