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Continental Drift - Glaciation

Glaciation in South America, Africa, India, and Australia is best
explained if these continents were once connected. Glaciers covered
all or part of each of these continents during the same time period in
the geologic past.

If the continents were in their present position, a major glaciation
event that covered nearly all of the continents and extended north of
the equator would be required. Geologists have found no evidence of
glacial action in the northern hemisphere during this time period. In
fact, during this time period, the climate in North America was warm.

Wegener proposed that the continents were adjacent to each other
during the glacial event. Therefore, glaciers spread over a much
smaller area in the southern hemisphere and probably did not influence
the climate of the northern hemisphere.

Wegener used the distribution of specific rock types to determine the
distribution of climate zones in the geologic past. For example,
glacial till and striations (scratches on the rock), sand dunes, and
coral reefs, indicate polar, desert, and tropical climates,
respectively. The present climate zones are shown in the above figure.
Note how the distribution of reefs, deserts, and glacial ice constrain
the position of the rotational pole of the Earth.

Using the distribution of rock types, Wegener reconstructed the
distribution of climates zones at specific times in the geologic past.
He found that, unlike the present distribution, in which zones
parallel the equator, the past zones occupied very different
positions. This implies that the rotational pole was in very different
locations relative to today. Wegener proposed an alternative
interpretation. He believed that the climate zones remained stationary
and the continents drifted to different locations. The drift of the
continents caused the apparent movement of the climate zones.

Wegener used the distribution of climate zones to determine the
location of the poles at different times in the geologic past. He
found that the rotational pole appears to gradually change location,
arriving at its present position only in the very recent geologic
past. The apparent movement in the pole position over time is called
polar wandering. Wegener offered an alternative explanation. He
suggested that the poles remained stationary and that the continents
changed their positions relative to the poles.
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References

1. file://localhost/vwdocs/vwlessons/plate_tectonics/part4.html
2. file://localhost/vwdocs/vwlessons/atg.html
3. file://localhost/vw.html
4. file://localhost/vwdocs/vwlessons/plate_tectonics/part6.html