STRUCTURE OF THE EARTH.

Manawatu Herald, Volume XLIX, Issue 3778, 12 April 1928, Page 1

STRUCTURE OF THE EARTH.

Observations on the rates at which earthquake shocks travel, make it at least highly probable that the greater jrart of the earth’s substance is homogeneous, says the scientific correspondent of the Tim-* es. That its interior has a high temperature is shown by the fact that all deep-seated rocks have either been melted or re-crystalised under great heat, by the molten condition of lavas extruded through the crust by the warmth of deep mines and the existence of hot springs. The average rise has been estimated at about ldeg. Fahr. for every 53ft. of descent. The inner mass is much heavier than the crust, the average specific gravity, or weight as compared with an equal bulk of pure water, being about 5.7 and of the crust about 2.5. The earth, moreover, is composed of zones. There is a central core which does not propagate earthquake shocks, occupies about one-fifth of the whole diameter, and probably consists of gaseous material, at a very high pressure; a massive portion in all probability composed of nickeliron, like meteorites; and an outer layer on the average 40 miles thick, very varied in its structure and composition, but with radio-active materials. All the continental masses are now regarded as being composed of what is called the “s'ial,” an acidified or partly oxidised Material of which silicon and aluminium are the characteristic elements. These and the great oceans are underlain by a basic material, known as the “sima” and composed largely of silicon and magnesium. The sial is lighter than the sima in which it floats, much as icebergs float in water, the depth to which the roots of. the continental masses are embedded in the sima depending on their size and weight. The modern view of the structure of the earth is that probably our solar system, like, other solar systems in the universe, has been formed by the aggregation of innumerable little meteorites instead of the cooling of an incandescent gas. The meteorites, as they came together, got heated by collision and pressure until they fused into a solid mass. Our world has been compared with an iron projectile, hardened like the projectiles of modern artillery, by nickel, and whirling through space. As it consolidated the metals settled down into the core, and the lighter stony materials formed a rusted or partly oxidised crust, like the slag in a furnace of molten iron.