Research on Earth's core

Press, Volume CXII, Issue 33061, 31 October 1972, Page 22

Research on Earth's core

(N.Z. Press Assn.—Copyright) PASADENA (California).

Scientists have a new weapon for research on the centre of Earth — a cannon which sends plastic projectiles smashing into mineral targets at 30,000 miles an hour.

Staff of the California Institute of Technology, say the gun, which will be first fired by January, 1974, will give insights into the composition of the Earth’s core as well as the cores of Mars, Jupiter and Saturn. For a brief instant — one-half-millionth of a second — the minerals struck by highspeed particles will be under the same intense heat and pressure they undergo at the centre of Earth, the scientists say. By controlling the speeds of the “bullets,” they expect to induce pressures up to 3.6 m times normal and temperatures as high as about 3900 deg. DOMINANT ELEMENT “For instance, we hope to be able to determine whether silicon or sulphur is the dominant element, alloying with iron, in the Earth’s

core,” said Dr Thomas Ahrens, an associate professor of geophysics, and the director of the project, which is supported by the National Science Foundation. “Silicon would imply a very high temperature when the Earth was formed, with the formation taking place rapidly. On the other hand, sulphur would suggest a considerably cooler Earth, and a slower growth.” Dr Ahrens has been experimenting for the last two years with a smaller gun that simulates conditions 600 miles below the Earth's surface. He says the experiments focus on careful measurement of the shock wave created by a particle when it slams into the target. “Shock-wave experimentation gives us different information than earthquake waves, which have produced most of what we know about the Earth’s deep interior,” he says. “Seismic waves tell us the velocity of waves through rocks at great depth. Shock-wave experiments, on the other hand, tell us the density as a function of pressure.” EARTHQUAKES

Dr Ahrens says the gun will also shed new light on how energy moves through the Earth and increase

knowledge about earthquakes and volcanoes. The 106 ft research gun will use a piston compressing hydrogen in a 60ft-long, 6in tube to launch the plastic projectile through an airless 20-ft tube. Dr Ahrens says that by controlling the speed of the piston, the tungsten • tipped plastic particles can be launched at any speed up to 30,000 m.p.h. Sensitive cameras and X-ray machines will measure the shock waves.