THE CONTINENTAL DRIFT HYPOTHESIS
A. BACKGROUND
Although the
"continental drift" hypothesis was proposed
by
a German meteorologist named
Alfred Wegener
in 1910,
he
was not the first to notice that the coasts
of Africa and South
America seem to
fit together. But
Wegener, working mostly
in the Southern Hemisphere, found other geologic
evidence
that convinced him that Africa and South
America had at one
time been joined together.
The purpose of today's lecture is to learn how
circumstantial
evidence can be used to support a scientific
hypothesis and
why this type of evidence, by itself, is
sometimes not enough
to convince the scientific community of a new
idea.
B. HYPOTHESIS
Based
on an apparent fit between Africa and South America,
Wegener hypothesized that at one time all
continents were
joined together in a "supercontinent"
called Pangaea.
The
supercontinent eventually broke into the
smaller continents,
which then "drifted"
towards their present positions.
Wegener supported his hypothesis by using
circumstantial
evidence, similar to the way that a detective would collect
evidence to solve a crime. There are four lines of
evidence:
In addition to
circumstantial evidence, geodetic surveys
also
appeared to directly support Wegener's
hypothesis.
C. RESPONSE
Most
geologists, especially those in North America, rejected
Wegener's hypothesis. One reason for
their skepticism was
the difficulty one encountered in
attempting to "fit"
continents
of the Northern Hemisphere back
together. But their biggest
objection was to the
mechanism Wegener proposed for how
the continents had "drifted"!