CENTRE OF EARTH.

Hauraki Plains Gazette, Volume XXXVI, Issue 4828, 1 April 1925, Page 1

CENTRE OF EARTH.

COMPOSED OF AN IRON CORE. SCIENTIFIC VIEWS. It is now generally agreed that the earth consists of an iron core surrounded by silicate rock. The earlier speculations concrening the density at various distance's from the centre, it is true proceeded on the assumption that the earth is essentially uniform in composition, and that the high internal density is due to compression under thc great pressures in the interior. But, beginning with the hypothesis by Dana in 1873, the notion of on. iron-cored earth has steadily gained credence among students of the subject.

What is certainly known is this: Somewhere within the earth is a very considerable; amount, of material intrinsically denser than any known silicate rock. This conclusion is reached most directly from studies based on. the compressibility of rocks and on. the velocity with which earthquake waves are transmitted through the earth.

Such studies have yielded a quantitative estimate on . the increase in density due to pressure at various depth, and have shown that, while the effect of pressure on density is a factor not to be neglected, it is nevertheless impossible to explain the high density of the earth on the basis of compressibility alone. That is, there must be at the centre some material which, under normal conditions, would be much denser than ordinary rocks would be.

The principal reason for assuming the dense; material in the interior to be mainly metallic iron is the analogy with meteorites. .Most of these visitors, from outer: space contain large .quantities of mietallic iron wit'a varying amounts ofl .nickel; and it does not demand an unwarranted use of the imagination? to regard meteorites as fragments, of disrupted bodies similar to, although probably much smaller than, bun, own planet, and io reason that the structure and average composition of these bodies are not very different from those of the barth.

The earlier picture of the earth’s metallic core, as presented by WiCr chert, was that of a central iron core separated by a rather sharp boundary from the surrounding silicate shell. More recently it has been suggested that between the core and the shell lies .a zone of mixed metallic iron and silicate rock, called pallasite from its supposed resemblance to a certain type of meteorites. The stony shell that surrounds the iron core is supposed to be gigantic near th* surface, and of basic (periodltic) character below.