At about the same time, in the mid-1950s, a series of articles by Boris Vasil'evich Timofeev (1916–1982) and his colleagues at the Institute of Precambrian Geochronology in Leningrad (St. Petersburg) reported discovery of microscopic fossil spores in Precambrian siltstones of the Soviet Union. In thin sections, like those studied by Tyler and Barghoorn, fossils are detected within the rock, entombed in the mineral matrix, so the possibility of laboratory contamination can be ruled out. But preparation of thin sections requires special equipment, and their microscopic study is tedious and time-consuming. A faster technique, pioneered for Precambrian studies in Timofeev's lab, is to dissolve a rock in mineral acid and concentrate the organic-walled microfossils in the resulting sludgelike residue. This maceration technique, however, is notoriously subject to error-causing contamination—and because during these years there was as yet no established early fossil record with which to compare new finds, mistakes were easy to make. Although Timofeev's laboratory was not immune, much of his work has since proved sound (Schopf 1992), and the technique he pioneered to ferret-out microfossils in Precambrian shaley rocks is now in use worldwide.
Early in the 1960s, the fledgling field was joined by two geologic heavyweights, an American, Preston Cloud (1912–1991), and an Australian, Martin Glaessner (1906–1989), both attracted by questions posed by the abrupt appearance and explosive evolution of shelly invertebrate animals that marks the start of the Phanerozoic Eon.
A feisty leader in the development of Precambrian paleobiology, Cloud was full of energy, ideas, opinions, and good hard work. His Precambrian interests were first evident in the late-1940s, when he argued in print that although the known Early Cambrian fossil record is woefully incomplete it is the court of last resort and, ultimately, the only court that matters (Cloud, 1948). By the 1960s, he had become active in the field, authoring a paper that to many certified the authenticity of the Tyler-Barghoorn Gunflint microfossils (Cloud, 1965) and, later, a series of reports adding new knowledge of the early microbial fossil record (Cloud and Licari, 1968; Cloud et al., 1975; Cloud and Morrison, 1980). But above all, he was a gifted synthesist, showing his mettle in a masterful article of 1972 that set the stage for modern understanding of the interrelated atmospheric-geologic-biologic history of the Precambrian planet (Cloud, 1972).
In the early 1960s, a second prime player entered this now fast-unfolding field, Martin Glaessner (1906–1989), of the University of Adelaide in South