Among the greatest natural historians was Alexander von Humboldt (1769-1859), who influenced Goethe, Darwin, and America's leading naturalists. Humboldt's Cosmos, published in five volumes from 1845 to 1860, stressed the unity of nature and discussed nature's vast details and unifying principles. He financed and led a scientific expedition to South America at the beginning of the 19th century, contributing profoundly to scientific knowledge of botany, geology, and zoology. Humboldt's careful measurements and descriptions also supported his speculations about more universal patterns in nature. Despite all that has been learned about the earth, we are assured that vast discoveries remain, The earth's ten-mile-thin crust is only the outer shell of a radius that is nearly 4,000 miles, and the deepest human exploration has been only five miles into a petroleum well. The biosphere, or "zone of live", provides the vast majority of materials to sustain life; it is (at most) 15 miles wide, including five miles of crust and five to ten miles of atmosphere. The base of information about earth has rapidly grown larger and more interconnected. Technological advances, combined with growing knowledge in the natural sciences, have enhanced the human power to create resources out of materials that have always been around us. Largely because of these advances, the earth now supports over 5 billion people at a standard of living undreamed of in the past. Humboldt understood this potential for improvement when he wrote that every acquisition won by (scientific) investigation is merely a step to the attainment of higher things in the eventful course of human affairs.