SIAL, SIMA AND NIFE

Waipa Post, Volume 38, Issue 2271, 21 February 1929, Page 3

SIAL, SIMA AND NIFE

THE EARTH'S "INTERNAL ORGANS."

(By G.P.)

Sial, Sima and Nife. These are not names of Egyptian, Chinese or Polynesian gods, but relatively recent additions to the vacabulary of geologists ,and they describe the now prevailing hypothesis about the general internal condition of the earth. They are surely not self-descriptive, and we must start by telling briefly what they mean. Sial is the name given to the outside shell of the earth's crust, sapposed to be composed everywhere of the lighter sort of rocks, listed as "acid" rocks. Sima is the corresponding name for the next lower shell, assumed to consist of denser, "basic" rocks. Nife is the name applied to the still more compact central core of the earth, which some believe is mostly, if not entirely, composed of iron. These names were constructed by the German geographer and geologist, Suess. Now, the middle shell, the sima, is assumed to be in a peculiar state, such, that, thought it is not 'liquid 1 ' in the ordinary sense, yet the sial (the upper shell on which we live), floats in it like a cork in water because of the difference of density. When you meet the word "isostacy" you may know that it refers to this hypothetical "floating" of the upper parts, or outer parts, of the earth in a denser crust beneath-, which is at the same time practically solid and potentially liquid. Don't bother. Trust mathematical physics to lay these extraordinary apparations of the conceptual world.

Now, a German geologist, Wegener, with a powerful imagination, has so to speak, made mincemeat of the sial (look back at the definition of the word). Suess and other geologists in general had assumed that the sial encloses the whole earth in a complete shell, being some sixty miles thick and underlying the oceans as well as the lands. But Wegener insists that tihe soal covers only about one-third of the globe, and that it has split up and drifted apart over the denser sima, which really does form a complete shell beneath. Look, says Wegener, at the strange outlines of the Americas on the east, fitting almost perfectly those of Europe-Africa on the west. Once they formed one mass of the sial, but the American portion has broken off, and floated away westward on the sima, and the Atlantic ocean, resting on the sima, now fills the gap. Of course this imagined voyaging of the continents over the surface of the globe is not supposed to have begun yesterday. It is a matter involving millions of years. But the hypothesis assumes that it is still going on. Earthquakes may be indications of it; volcanic eruptions may result from the pulls and squeezes that it brings about.

The sial, sima and nife have been accepted as geological terms to describe the probable tri-partite division of the earth's crust into concentric sheila; but Wegener's extraordinary hypothesis is still knocking at the door, with perhaps not too brilliant prospects of admission.