麻豆淫院

(麻豆淫院Org.com) -- For a century, scientists have assumed that the Earth has same chemical make-up as the sun. But this belief has been challenged by scientists at The Australian National University.

Professors Ian Campbell and Hugh O鈥橬eill from the Research School of Earth Sciences at ANU said their research shakes up our understanding of the Earth鈥檚 chemistry 鈥� right to the core.

鈥淔or decades it has been assumed that the Earth had the same composition as the Sun, as long the most volatile elements like hydrogen are excluded. This theory is based on the idea that everything in the solar system in general has the same composition. Since the sun comprises 99 per cent of the solar system, this composition is essentially that of the sun,鈥� Professor O鈥橬eill said.

As it is easier to measure the chemical make-up of chondritic meteorites, planetary geologists have long used these to more precisely determine the sun鈥檚 composition 鈥� and therefore the composition of the Earth. From this, scientists have concluded that the Earth has a 鈥榗hondritic鈥� composition.

Professor Campbell said this thesis has been challenged again and again.

鈥淩ecent discoveries have shown that the ratio of two of the rare earth elements in Earth鈥檚 volcanic rocks is higher than in chondritic meteorites. Many scientists have explained this by arguing that there must be a hidden reservoir of these elements near the centre of the Earth to balance this ratio out. This reservoir would also be enriched in the heat producing elements uranium, thorium and potassium,鈥� he said.

Professor Campbell spent twenty years researching mantle plumes 鈥� columns of hot rock that rise from the boundary of the Earth鈥檚 core and are the mechanism that removes heat from the Earth鈥檚 centre.

鈥淭he problem with the idea of a hidden reservoir is that although these elements could be hidden we would be able to detect the heat they produce,鈥� he said.

鈥淗owever, mantle plumes simply don鈥檛 release enough heat for these reservoirs to exist. As a consequence the Earth simply does not have the same composition as chondrites or the sun.鈥�

Professor O鈥橬eill has developed an explanation as to why the Earth鈥檚 composition may differ from chondrites.

鈥淭he Earth is thought to have formed by collision of planetary bodies of increasing size. In our research we suggest that by the time these planetary bodies had reached a moderate size they developed an outer shell that contained a significant amount of heat-producing elements,鈥� he said.

鈥淒uring the final stages of the Earth鈥檚 formation this outer shell was lost by a process called 鈥榗ollisional erosion鈥�. This produced an Earth that has fewer heat producing elements than chondritic meteorites, which explains why the Earth doesn鈥檛 have the same chemical composition as chondritic meteorites.鈥�

The research has been published in Nature.