David Brin Quote

It also became clear why the nations were expected to commence major space enterprises. Henceforth, the raw materials for industrial civilization were to be taken from Earth's lifeless sisters, not the mother world. All mines currently being gouged through Terra's crust were to be phased out within a generation and no new ones started. Henceforth, Earth must be preserved for the real treasures—its species—and man would have to look elsewhere for mere baubles like gold or platinum or iron.

Part XI (pp. 634-635) - Earth (1990)