Gold deposits are formed via a very wide variety of geological processes. Deposits are classified as primary, alluvial or placer deposits, or residual or laterite.

Download Neobux Money Adder Software Definition. • • • • The idea that gold came from outer space sounds like science fiction, but it has become well-established - it's pretty much received opinion in the field of earth sciences. How did this bizarre theory take hold, and is it here to stay?

For the chieftains of pre-Columbian America, the dazzling yellow stuff they found glinting at the bottom of streams or buried in the rocky ground captured the power of the sun god. They dressed themselves in battle armour wrought from the enchanted metal, believing it would protect them. They were sadly deceived. Gold, an unusually soft metal, wasn't any match for the steel of the Spanish. But the Native Americans may well have been right in believing the element was otherworldly. 'Why do you find nuggets of gold on the surface of the Earth?' Asks science writer John Emsley.

'The answer to that, is that they've arrived here from space in the form of meteorites. South Park Mexican When Devils Strike Rarity here. ' This theory has come in the last few decades to be held by the majority of scientists as a way of explaining gold's abundance. There may only be 1.3 grams of gold per 1,000 tonnes of other material in the Earth's crust (the rocky shell of the planet that is around 25 miles thick) but that's still too much to fit with the standard models of our planet's formation. 'They are basically the building blocks of Earth,' says Willbold. Two years ago, he and a team from the universities of Bristol and Oxford examined some rocks from Greenland which had their origins in a part of the Earth's mantle that was insulated from meteorite activity for a crucial period some 600 million years. The team did not look at the gold content of the 4.4-billion-year-old rocks, but at tungsten. Tungsten has some similarities to gold but exists in different forms or isotopes, and this provides scientists with more historical information.

'The tungsten-isotopic composition of these rocks was basically really different from the tungsten-isotopic composition of other rocks,' says Willbold. He infers that the Greenland rocks are a remnant of Earth's composition prior to the start of the late veneer meteorite shower, postulated to have taken place between 4.4 and 3.8 billion years ago. The Why Factor is broadcast on BBC World Service on Fridays at 18:30 GMT • • • Willbold's influential study, published in Nature in September 2011, provides the most compelling evidence yet for the late veneer hypothesis. This hypothesis seems the best explanation for the unusual tungsten-isotopic profile of Willbold's Greenland rocks, just as it seemed to explain the different quantities of gold and iridium in the mantles of the Earth and the Moon in the 1970s.