An Ancient Planet Beneath A Youthful Veneer

Gerald Wesserburg and Donald de Paolo, two California geologists, have studied the isotopic ratios of neodymium 143 and 144 in both continental and deep-sea lavas. If the underground lava sources were the same, the isotope ratios should be the same. But they are not. Midocean lavas are enriched in neodymium143 compared to continental lavas. Since neodymium-143 is a decay product of samarium, scientists have been able to establish the neodymium isotope ratio from the time of the Big Bang to the present.

The isotope ratio for the mid-ocean lavas is just what would be expected on a planet where lighter surface materials had come to the surface during a molten state. The continental lavas, though, must tap very ancient reservoirs, possibly those of a true primitive earth. This ancient core is now swathed with younger materials from who knows where! This young envelope wraps around the whole planet, with the present continents being caused by slight protuberances on the ancient core. Whence the young veneer? A rain of material from some recent close encounter?

(Anonymous; "Underground Sites of Ancient Earth," New Scientist, 83:886, 1979.)