“. (a). Had Earth ever been molten, dense, nonreactive chemical elements such as gold would have sunk to Earth’s core. Gold is 70% denser than lead, yet is found at the Earth’s surface (b). Therefore, the entire Earth was never molten and did not form by meteoritic bombardment.”
It is a well known fact that metals dissolve in each other. These solutions are called ALLOYS.
Do this simple experiment:
Take a glass and half fill it with water.
Put three teaspoons of sugar into the glass. The sugar, being heavier than water, sinks to the bottom.
Using a spoon, stir until the sugar dissolves. Cover the glass and put it in an ant free place and let it stand for a week.
Then take a straw, lift off the cover and suck up the water from the bottom of the glass. If a above was true the water at the bottom of the glass would be much sweeter that that at the top, because sugar is heavier than water.
If the whole glass is equally sweet then a above is wrong and so is b.
Do the experiment. Don’t believe all you read.
“a. “The kinetic energy (~5 x 10^38 ergs) released in the largest impacts (1.5 x 10^27 g at 9 km/sec) would be several times greater than that required to melt the entire Earth.” George W. Wetherill, “Occurrence of Giant Impacts during the Growth of the Terrestrial Planets,” Science, Vol. 228, 17 May 1985, p. 879. “
The worthy George W. Makes several false assumptions.
i) We know the mass and relative velocity of the proto-earth and the impactor. In fact we know none of these so George .W. is making assumptions to fit the conclusion he wants to draw.
ii) All the energy of the impact or is converted into heat and the heat is all transferred to the new combination.
This is contrary to what is observed. At the point of impact extremely high temperatures are reached causing a great deal of energy to be radiated into space.
http://en.wikipedia.org/wiki/Kirchhoff's_law_of_thermal_radiationiii) Substantial amounts of material are ejected into space after such an impact. Just look at the craters on the moon.
iii) The momentum of the impactor would be shared by the proto earth
http://en.wikipedia.org/wiki/Momentum Thus not all of the kinetic energy would have been dissipated as heat.
Even if all the good George W. was correct, all it would mean would be the earth had been melted several times. It would cool down rapidly after each impact. See Kirchhoff’s law above.
“b. If gold were found only near volcanoes, then one might claim that gold was brought up to the Earth’s surface by volcanoes. However, gold is seldom found near volcanoes.”
This sentence seems to be a waste of space.
In fact, as this article shows, gold is found associated with long extinct volcanoes
http://www.cprm.gov.br/33IGC/1315736.html“Suppose extremely hot salt water (932°F or 500°C) circulated under the crust—a crust that had never been molten.”
This theory has since been refuted:
Scientists Discover That 40 Percent Of The World's Gold Is 3 Billion Years Old
ScienceDaily (Sep. 16, 2002) — Scientists have for the first time directly dated gold from South Africa's Witwatersrand gold deposits, source of more than 40 percent of all gold so far mined on Earth.
An international team of geologists led by the University of Arizona has discovered that the gold is around 3 billion years old -- older than its surrounding conglomerate rock by a quarter of a billion years.
More, their state-of-the-art dating technique shows that the gold deposits formed along with crustal rock directly from the mantle beneath South Africa. The event at this magnitude appears to be unique in Earth's geologic history.
Jason Kirk, Joaquin Ruiz and John Chesley of the UA, John Walshe of Australia's Commonwealth Scientific and Industrial Research Organisation, and Gavin England of the University of Edinburgh report on it in the Sept. 13 issue of Science.
The Witwatersrand gold is found in a sedimentary basin. But the age and origin of the gold has been hotly debated. One theory argues that the gold was carried into the basin by sedimentary processes. A conflicting theory holds that the gold was emplaced by hydrothermal fluids -- the equivalent of hot springs -- from the upper continental crust.
The new results confirm that the Witwatersrand gold deposits are "placer" deposits -- that millions of years ago, ancient rivers carried gold particles, along with sand and silt, into the Witerwatersrand basin -- then a great lake -- possibly from granite mountains to the north and southwest.
Over time and under pressure, the gold-bearing sediments solidified into rock, forming the rich gold-bearing reefs of South Africa's 'golden arc,' which have been mined since their discovery in 1886.
The UA scientists' new findings confirm that the gold first formed in older rocks, rocks that formed when upwelling mantle formed a major piece of South African continental crust called the Kaapvaal craton. Cratons are areas of Earth's crust that have remained tectonically stable over time. The Kaapvaal craton is one of the oldest known.
Later, the gold was weathered and reconcentrated in the Witwatersrand paleolake sediments.
Kirk is studying the age and extent of gold deposits around the world for a UA doctoral geosciences degree. He uses a rhenium-osmium isotope gold-dating technique developed by Ruiz at the university's NTIMS laboratory.
Ruiz, dean of the UA College of Science and professor of geosciences, was instrumental in developing the Negative Thermal Ionization Mass Spectrometer (NTIMS) with a grant from the W. M. Keck Foundation. The laboratory is one of the few of its kind in the world.
"This is precisely the kind of research that I envisioned when I was building the laboratory," Ruiz said. "The analytical capabilities of the W.M. Keck Laboratory is such that we will continue to discover aspects of how the Earth worked, questions that previously we could only dream of."
Gold and other minerals contain a rare metallic chemical element called rhenium. Rhenium-187 is the radioactive form of the element. NTIMS directly dates minerals by counting the number of their rhenium-187 and osmium-187 atoms. Rhenium-187 has a half -life of 45 billion years, or about 10 times the age of our solar system. It decays into osmium-187. So by determining the ratio of radioactive rhenium-187 to daughter osmium-187 atoms, scientists can directly calculate when the minerals formed.
"One of the reasons I think our results are so significant is that the rhenium-osmium system can be used directly on gold, and can also tell us if the gold came from the mantle or the crust," Kirk said.
There is relatively more rhenium than osmium in Earth's crust, but relatively more osmium than rhenium in Earth's mantle.
"Witwatersrand has a clear mantle signature," Kirk said. "It's possible that this mantle signature is so big because at 3 billion years ago, Earth's mantle might have been hotter, and richer in gold at this particular spot, compared to more recent deposits."
People, understandably, are keenly interested in why South Africa has been so blessed with gold. The Witwatersrand gold fields have yielded a half-trillion dollars' worth of gold since 1886.
"Estimates are that there's another half-trillion dollars in gold still to be mined, and that's a lot of money," Kirk said.
