The Earliest History of Life: Solution to Darwin's Dilemma

In 1859, Darwin stated the problem: “If the theory [of evolution] be true, it is indisputable that before the lowest Cambrian stratum was deposited … the world swarmed with living creatures. [However] to the question why we do not find rich fossiliferous deposits belonging to these earliest periods … I can give no satisfactory answer. The case at present must remain inexplicable; and may be truly urged as a valid argument against the views here entertained.” For the following century, until the mid-1960s, the missing Precambrian fossil record stood out as among the greatest unsolved problems in natural science.

In the 1880s, '90s, and early 1900s, Charles Doolittle Walcott (1850-1927) made the pioneering discoveries -- Precambrian stromatolites, phytoplankton (Chuaria), and the famous Cambrian-age Burgess Shale Fauna -- and in 1914 he reported fossilized bacteria from Precambrian limestones of Montana. But neither the bacteria nor the earlier-reported stromatolites gained acceptance. In 1950, Boris Vasil'evich Timofeev (1916-1982) reported plant spores from the Precambrian of the Soviet Union, yet these, too, were widely questioned. Soon thereafter, Stanley A. Tyler (1915-1984) and Elso S. Barghoorn (1915-1984) announced the discovery of microbial fossils in the Precambrian Gunflint chert of southern Canada. The breakthrough publications date from 1965: Barghoorn and Tyler formally described the Gunflint fossils; Preston Cloud (1912-1991) validated the find; and Barghoorn and I reported much better preserved fossil microbes from the Precambrian of central Australia. This last report, followed by a monograph in 1968, suggested that such fossils were not uncommon and established the search-strategy used to the present. From these beginnings, the documented history of life has been extended to 3,500 million years ago, some seven times earlier than was previously known. The missing Precambrian fossil record has been discovered; what was once "inexplicable" to Darwin is no longer so to us.