Page 78 - Handbook of Gold Exploration and Evaluation

Nature and history of gold 59

to the rate which the distant cluster recedes' then became the basis of the `Big
Bang' theory. Photography of stellar spectra became routine and in the mid
1940s, a German physicist, C. von Weizsacker, from theory and laboratory
evidence proposed that a cloud of gas and dust rotating about a central body
would develop vortices and eddies.
Discoveries such as these in planetary science stimulated a resurgence of
efforts seeking to learn more about the Earth and its neighbours in space. Many
theories have since developed including the `steady state' theory, which assumes
that matter is being continually created; the fresh matter forming new galaxies to
replace galaxies that have moved to infinite distances. Models suggested by
astronomers represent the universe as expanding, contracting and oscillating
(expanding then contracting) or static (neither expanding nor contracting).
Discovery of the cosmic background radiation of a body by Penzias and Wilson
of Bell Telephone, while experimenting with a very sensitive microwave
antenna, has been the strongest confirmation of the Big Bang theory. A hiss,
corresponding to radiation of a body at a temperature of ÿ454 ëF, was dis-
covered at a wavelength of 7.34 cm with an intensity that seemed independent of
the orientation of the antenna. This is the temperature to which the Earth is
expected to have cooled as a result of its expansion since the Big Bang. There
seem to be two possibilities (Brecher, 2002):
· If no more matter exists than is detected to date, the universe would expand
indefinitely and stars would eventually exhaust the energy that makes them
shine.
· If the universe contains large amounts of dark matter, i.e., material not yet
detected, the expansion would stop in perhaps 20±40 billion years. The
galaxies would then come together again and matter would approach infinite
density. This cycle of collapse and expansion could then be repeated
indefinitely.
The solar system is thought to have developed about five billion years ago
from the accumulation of planetismals (meteorites and asteroids) at about
absolute zero temperature. Earth has been kept alive by the flow of energy from
its molten interior. This may continue for another 4±5 billion years before all of
the heat supply has been dissipated. Virtually all of the other planetary bodies in
the system are geologically dead except perhaps Mars. The first life forms on
Earth, thermophilic (heat-loving) bacteria, have been found throughout its
known geological history and Earth remains both geologically and biologically
active. Mars is believed to have had a brief period of running water about 3,600
years ago; fossil thermophilic bacteria are recorded from carbonate inclusions,
dated to 3,600 years ago within a Martian meteorite found in the Antarctic
(Plimer, 1997).
The first individual radio telescopes had poor resolving ability. For example,
the angular resolution of a 25 m radio telescope observing at 1 m wavelengths is