The first billion years: new insights from geochemistry

Prologue: (V)ast globes. . . after reaching the last stages of ebullition, were coveredwith scoriae like bubbling foam. And the crust which covered the molten matter of the globe and which hardened from the fused condition would be like scoria, as happens with metals in the furnace. If then the great framework of the earth, the exposed rocks, the imperishable silicates, are almost entirely vitrified, does that not prove that they arose from a fusion of bodies, brought about by the powerful action of nature’s fire on still soft material? It is everywhere true that the most simple and primitive material in the composition of the earth, that which represents most accurately the true nature of rocks, is that which most resists fire, which melts [only] under an excessive heat, and finishes by vitrifying. . .