LECTURE

distorted the past. They highlighted the activities of the literate and could say nothing about the history of the natural world or of anything that existed before the invention of writing. The idea that history could only be based on written documents created a sense of separation between human history and the history of the natural world. Written evidence could also deceive. Christian theologians, such as Eusebius of Caesarea (who died c. 340 C.E.), used written evidence from the Old Testament to date the moment of creation to about 4000 B.C.E. Their evidence-based calculations would dominate Christian cosmology for 1,500 years.

From the 17th century, new evidence began to undermine this chronology. Seventeenth-century geologists already doubted the traditional Christian timescale of 6,000 years. For example, the nding of marine fossils in mountains suggested that mountains had once been under the sea, which suggested they had been created over vast periods of time.

In 1795, James Hutton (1726–1797) argued that the Earth’s surface had been formed by slow processes such as erosion and uplift, acting over unimaginably long periods of time. By his time, it was possible to generate relative dates for the Earth’s history (saying what order things occurred in by using the fossils in different strata), but he despaired of constructing an absolute chronology. As late as the early 20th century, written records remained the basis for chronology. When, just after World War I, H. G. Wells attempted a form of big history in his Outline of History, he knew that he had no precise dates before the 1st millennium B.C.E.

The situation was transformed in the middle of the 20th century by a second “chronometric” revolution. The discovery of radioactivity provided the crucial breakthrough. Marie (1867–1934) and Pierre (1859–1906) Curie discovered radioactivity, and both eventually died of cancer caused by handling radioactive substances. A New Zealand–born physicist, Ernest Rutherford (1871–1937), showed that radioactive materials break down with great regularity, so that in principle they could be used as clocks. In the 1950s,

The rst “chronometric” revolution was the appearance of writing, about 5,000 years ago.