Page 74 - Handbook of Gold Exploration and Evaluation

Nature and history of gold 55

upon a long life for the deposits. One hundred and forty years of intensive
mining has resolved the question of size and value of gold deposits in the
Witwatersrand, but the evidence is still inconclusive as to their source (see
Chapters 3, 5 and 6).

1.2.8 Scientific advances of the 20th century
By the turn of the 20th century scientists such as the Curies, Einstein and
Rutherford showed that radioactive elements within the Earth constitute an
enormous source of energy that can be harnessed for mankind's good (or evil).
Quantum mechanics, flowing from Max Planck's attempts to describe the
behaviour of molecules, atoms and sub-atomic particles, provided a completely
different kind of mathematics involving quantum theories. Discovery of the
electron saw the birth of particle physics and, through the mathematics of
quantum mechanics and experimental observation, several tenets of Newtonian
physics were abandoned. Experiments showed that electrons could behave as
waves when they are diffracted on passing through crystals. In 1900, Max
Planck stated that substances emit light only at certain energies, and that
electromagnetic radiation could be emitted only in specified amounts that he
called quanta. Einstein in 1905 used the Planck theory on radiated energy theory
to account for the discovery that light as electromagnetism travels in a vacuum
at a fixed speed in every direction. His General Theory of Relativity introduced
differential geometry into physics as a description of Nature. The science of
particle physics emerged with the concept of particles as points moving through
space along a line called the World Line. Two of the predictions of this theory
have been the concept of an expanding Universe and black holes, both of which
encapsulate issues in mathematical terms of reality and existence.
By 1911, Ernest Rutherford had established that the atom has a positive
nucleus surrounded by orbiting electrons. In 1913, Niels Bohr calculated the
quantum of the simplest case, hydrogen, in which a single electron orbits a
proton. He showed that the quantum restricts the electron to particular orbits and
that for each counting number (1, 2, 3, . . .) there was one permissible orbit.
Light is emitted when the electron changes from a higher quantum number to a
lower one. There was not a continuous spectrum because the electron moves in
jumps (quantum jumps) from one orbit to another. Scientists extended Bohr's
model to explain both large and smaller lines in the spectrum and a second
quantum number was introduced to explain the fine structure.
With some notable exceptions, the common view of most (although not all)
geologists at the start of the 20th century, was that continents were locked in
place and oceans were formed in areas where lateral compression causes
sections of the Earth to subside. However, even as far back as 1596, Abraham
Ortelius in his work Thesaurus Geographicus had suggested that the Americas
were `torn away from Europe and Africa ± by earthquakes and tides'. Further,