Sydney, Apr 2 (IANS): Scientists are rejecting a century-old assumption that the earth has the same chemical makeup as the sun.

"This theory is based on the idea that everything in the solar system in general has the same composition," said Hugh O'Neill, professor at the Research School of Earth Sciences at The Australian National University and study co-author.

"Since the sun comprises 99 percent of the solar system, this composition is essentially that of the Sun," O'Neill said.

As it is easier to measure the chemical makeup of chondritic (stony) meteorites, geologists have long used these to more precisely determine the sun's composition - and therefore the composition of the earth, the journal Nature reported.

From this, scientists have concluded that the earth has a 'chondritic' composition, according to a university statement.

"Recent discoveries have shown that the ratio of two of the rare earth elements in earth's volcanic rocks is higher than in chondritic meteorites," said Ian Campbell, professor and study co-author from Research School of Earth Sciences.

Campbell spent 20 years researching mantle plumes - columns of hot rock that rise from the boundary of the earth's core and are the mechanism that removes heat from the earth's centre.

"However, mantle plumes simply don't 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," he added.