Download Alfred Wegener

The PLATE TECTONIC THEORY
Alfred Wegener
In the early part of the
20th century he noticed
how continents seemed
to “fit” together.
He wondered if the
continents had once all
been connected
Alfred Wegener
So in 1912 he published his
theory: That 180-200
million years ago there was
only one giant continent on
Earth.
He named this
supercontinent “Pangaea”
meaning “all-Earth.”
Continental Drift Theory
Wegener’s theory was that the continents
had moved, or “drifted” from an earlier
position, to their present locations.
He had four key pieces of evidence to support
his radical Continental Drift Theory.
Continental Drift Theory
1. They Fit – Darn it! They just look like they
should fit together!! (And the continental
shelves fit even better!)
Continental Drift Theory
2. Matching geological structures - similar rock
formations were found on continents
thousands of kilometres from each other.
Continental Drift Theory
3. Matching Fossils - He noticed that fossils of
identical animals were being found on
continents separated by thousands of
kilometres.
Continental Drift Theory
4. Climatic Evidence – Paleoglaciation
- Evidence in tropical areas that they had
once had glaciers, and evidence that cold
areas (like Antarctica) had once been tropical.
Continental Drift Theory
Unfortunately, Wegener couldn’t explain how
the continents moved. The response from
the scientific community of the time was...
The Evidence Builds
 Not long after Wegener’s death it was discovered
that Earth’s surface is broken into big chunks called
“tectonic plates.”
The Evidence Builds
 New scientific equipment allowed scientists to
measure the slow but steady drift of Earth’s
tectonic plates.
 It was noted that earthquakes and volcanoes
appear in certain patterns along the edges of
tectonic plates.
 Mapping of the ocean floor revealed the MidAtlantic Ridge, a long mountain range running
down the middle of the Atlantic Ocean.
The Evidence Builds
 Dating the rock around the
M.A.R. gave surprising
results.
 Rocks near to the ridge
were younger than rock
further away.
 Then, magnetic reversal
was discovered. This
pattern was the same on
both sides of the ridge.
The Evidence Builds
 Geologist H. Hess
proposed a theory to
explain – magma beneath
the surface rises and forms
a new sea floor,
continuously pushing
older rock away.
 Hess called this sea floor
spreading.
The Evidence Builds
 Canadian geologist J.T. Wilson theorized that
continents must move. This explained the formation
of mountains, oceans, and the cause of earthquakes
and volcanoes.
 This was named the Plate Tectonic Theory, and is
considered the unifying theory of geology.