Wat weet ons van die aarde?

Inaugural lecture--Department of Geology, Rand Afrikaans University, 10 March 1969@@The present state of our knowledge concerning the internal composition of the earth is summarized and discussed. It is pointed out that the interior of the earth may consist of matter similar in composition to meteorites, but that there is also a possibility that it may consist of high-density material unknown to us at present. The nature of continents and oceanfloors is discussed, and reference is made to the results of palaeomagnetic investigations and to the theory of oceanfloor spreading. In discussing the cause of the spreading it is shown that this may be due to either convection currents or to an expanding earth. Mention is made of the controversies which exist regarding the origin of rocks. It is pointed out that the occurrence of basic complexes such as the Bushveld Complex and the Great Dyke of Rhodesia between mobile belts indicates that the origin of these complexes may be controlled by continental block movements. The distribution of economic minerals is briefly discussed and the possibility of finding similar deposits in the oceanic crust is mentioned. Finally the role of the geologist in the future development of our country is reviewed.