SYDNEY, 15 June 2006 - There is enough gold within the core of planet Earth to coat its surface to a depth of half a metre, according to a paper by a Macquarie University scientist in today's edition of the science journal, Nature. The researchers believe that more than 99 per cent of the Earth's gold is at the heart of our planet.

In the paper, Bernard Wood, a Federation Fellow within the ARC National Key Centre for Geochemical Evolution and Metallogeny of Continents (GEMOC) at Macquarie University and Michael Walter and Jonathan Wade of the University of Bristol, U.K., described how the Earth was shaped over millions of years from smaller 'planetesimal' building blocks crashing together, and how its core was formed by ensuing chemical processes.

The researchers said the Sun's planetary system formed from a flattened disk of dust and gas which quickly (in less than 10,000 years) became planetesimals less than 10 kilometres in diameter. Radioactive dating indicates that it then took the next 100,000 to one million years to generate Moon-to-Mars sized planetary embryos from gravitational interactions and collisions between these planetesimals. Larger planets formed over the next 10-100 million years.

"In the case of our own planet, it took 30-40 million years for the planetesimals to form essentially what we now know as the Earth," explains Wood.

"What's particularly interesting in terms of the Earth's formation is that many of these planetesimals had metallic iron cores. During the Earth's growth, the planet was covered by a hundreds of kilometres deep ocean of molten rock and the metal reacted with this rock, extracting many of the most important and interesting elements and depositing them in the Earth's own iron-rich core.

"For example, by comparing the composition of the Earth's crust with that of the planetesimals (represented by meteorites) we can say that more than 99 per cent of the Earth's gold is in the core."