To many it may seem presumptuous of anyone to attempt to unravel the mysteries surrounding the origin of the Earth and, in a wider sense, of the Universe itself; to others it may even seem irreverent that the great act of Creation should be regarded as a field for scientific speculation. In his pursuit of knowledge of the external world the scientist, however, is not held within precise limits of time, past or future; for example, the measure of progress in astronomy through the ages can be expressed, in some respects at least, in terms of the increasing capacity of man to see still further into the future and to peer still more deeply into the mists of the past.