Abstract
In 1859, C. R. Darwin highlighted the “inexplicable” absence of evidence of life prior to the beginning of the Cambrian. Given this lack of evidence and the natural rather than theological unfolding of life’s development Darwin espoused, over the following 50 years his newly minted theory was disputed. At the turn of the 19th century, beginning with the discoveries of C. D. Walcott, glimmerings of the previously “unknown and unknowable” early fossil record came to light – but Walcott’s Precambrian finds were also discounted. It was not until the breakthrough advances of the 1950’s and the identification of modern stromatolites (1956), Precambrian phytoplankton in shales (1950’s), stromatolitic microbes in cherts (1953), and terminal-Precambrian soft-bodied animal fossils (1950’s) that the field was placed on firm footing. Over the following half-century, the development and application of new analytical techniques coupled with the groundbreaking contributions of the Precambrian Paleobiology Research Group spurred the field to its international and distinctly interdisciplinary status. Significant progress has been made worldwide. Among these advances, the known fossil record has been extended sevenfold (from ∼0.5 to ∼3.5 Ga); the fossil record has been shown consistent with rRNA phylogenies (adding credence to both); and the timing and evolutionary significance of an increase of environmental oxygen (∼2.3 Ga), of eukaryotic organisms (∼2.0 Ga), and of evolution-speeding and biota-diversifying eukaryotic sexual reproduction (∼1.2 Ga) have been identified. Nevertheless, much remains to be learned. Such major unsolved problems include the absence of definitive evidence of the widely assumed life-generating “primordial soup”; the timing of the origin of oxygenic photosynthesis; the veracity of postulated changes in global photic-zone temperature from 3.5 Ga to the present; the bases of the advent of eukaryotic sexuality-requiring gametogenesis and syngamy; and the timing of origin and affinities of the small soft-bodied precursors of the Ediacaran Fauna.
Highlights
In 1859, Charles Robert 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. [Yet] why we do not find rich fossiliferous deposits belonging to these assumed earliest periods
The introduction of secondary ion mass spectrometry (SIMS) in the field of geochemistry, where it was primarily applied to analyzing the carbon isotopic composition of isolated Archean zircon grains, represented a promising opportunity to Precambrian paleobiology by which to document the metabolism-indicating carbon isotopic signatures of individual microscopic fossils
confocal laser scanning microscopy (CLSM) is a highly effective research tool and the only technique available for complete morphological investigation of minute fossils rock-embedded at depth, permitting their images to be rotated parallel to the thin section surface and viewed from multiple perspectives
Summary
Unlike the Editors and publishers of this volume, please note that I prefer to refer to this field of science as “Precambrian Paleobiology” – rather than “Precambrian Paleontology” – because the suffix “-biology” emphasizes its necessarily interdisciplinary character, a hallmark of the field that contrasts rather markedly from the long-established practices of Phanerozoic. Being the last surviving member of the so-called “vanguard” of workers in such Precambrian studies (Cloud, 1983) and having spent some 60 years investigating numerous aspects of the early history of life, please note that this review article is written from my personal perspective
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