In this exercise, you will examine the shorelines of South America and Africa (o

Question

In this exercise, you will examine the shorelines of South America and Africa (or evidence of the theory of plate tectonics. (a) Sketch the shorelines of South America and Africa from the figure below on separate pieces of tracing paper. Rearrange the continents so that they fit as well as possible without overlapping or leaving large gaps. How well do the continents fit? Where are the problem areas? (b) Are the current shorelines of South America and Africa accurate representations of those continents when they were rifted apart? What factors other than rifting and seafloor spreading could have modified the shape of the current shorelines?

Explanation / Answer

(a) The continents fit perfectly well. The coastlines of South America and Africa fit perfectly well like that of a jigsaw-puzzle.

The problem areas are the gaps and overlaps in the jigsaw-puzzle like fit of the coastlines on the Western and Eastern part of the Atlantic Ocean i.e. that of the coastlines of South America and Africa. Moreover, continental crust extends well beneath the continental shelf areas to the continental slope; thus, the fit is not made on coastlines.

The overlaps are of geological significance as they were created due to the thinning and thickening of the oceanic crust i.e. formation of rifted continental margins accompanied by processes of extension and stretching. Iceland was created during the opening of the Atlantic (Cenozoic) and its presence outdates the continental reconstruction. The Bahama Platform on the South American coastline overlaps the African continent. The Bahama Platform essentially consists of corals created when the two Americas (North and South) separated. The Niger Delta also experiences overlap. The Caribbean Sea is absent.

(b) No, the current shorelines of Africa and South America are not accurate representatives of the continents when they were rifted apart, because of some gaps, overlaps and mismatches.

Palaeontological and Climatic factors other than sea floor spreading and rifting has modified the current shorelines.

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