Organism motility in an oxygenated shallow-marine environment 2.1 billion years ago

Abstract

Evidence for macroscopic life in the Paleoproterozoic Era comes from 1.8 billion-year-old (Ga) compression fossils [Han TM, Runnegar B (1992) Science 257:232–235; Knoll et al. (2006) Philos Trans R Soc Lond B 361:1023–1038], Stirling biota [Bengtson S et al. (2007) Paleobiology 33:351–381], and large colonial organisms exhibiting signs of coordinated growth from the 2.1-Ga Francevillian series, Gabon. Here we report on pyritized string-shaped structures from the Francevillian Basin. Combined microscopic, microtomographic, geochemical, and sedimentologic analyses provide evidence for biogenicity, and syngenicity and suggest that the structures underwent fossilization during early diagenesis close to the sediment–water interface. The string-shaped structures are up to 6 mm across and extend up to 170 mm through the strata. Morphological and 3D tomographic reconstructions suggest that the producer may have been a multicellular or syncytial organism able to migrate laterally and vertically to reach food resources. A possible modern analog is the aggregation of amoeboid cells into a migratory slug phase in cellular slime molds at times of starvation. This unique ecologic window established in an oxygenated, shallow-marine environment represents an exceptional record of the biosphere following the crucial changes that occurred in the atmosphere and ocean in the aftermath of the great oxidation event (GOE).

Microbially induced potassium enrichment in Paleoproterozoic shales and implications for reverse weathering on early Earth

“…Here, we present whole-rock and in situ geochemical analyses, bulk XRD, electron microscopy images, and synchrotron-based elemental distribution maps from MRS and their host sediments. We studied samples from a 15-m-thick, coarse-grained sandstone that conformably underlies a 5-m-thick, thinly-bedded black shale that hosts the oldest large colonial macrofossils with evidence for organism motility previously described from the FB 2 Member of the FB Formation 28–30 (Supplementary Fig. 1b).…”

Ichnofossils, Cracks or Crystals? A Test for Biogenicity of Stick-Like Structures from Vera Rubin Ridge, Mars

“…A metazoan-like bodyplan is not essential for producing macroscopic traces, as evidenced by microbial-related structures in Ordovician low-oxygen environments [68]. Microorganisms can even produce macroscopic trails or burrows, as evidenced by 2.1 Ga ichnofossils attributed to multicellular or syncytial organism able to migrate laterally and vertically [69]. These non-metazoan macroscopic ichnofossils encourage research of extraterrestrial analogues, i.e., ichnofossils produced by the aggregation of amoeboid cells into a motile slug-like phase, similar to that of terrestrial slime molds.…”

“…Second, they are resilient to processes that obliterate other biosignatures, as evidenced by trace fossils preserved in metamorphosed and highly tectonized rocks [73][74][75]. Because of their preservation potential and abundance, ichnofossils are among the most abundant evidence of microscopic and macroscopic past life, as exemplified by 3.7 billion-years-old stromatolites [76], 2.1 billion-years-old burrows [69], and ca. 551 million-years-old trackways [77].…”

A review of biotic signatures within the Precambrian Vindhyan Supergroup: Implications on evolution of microbial and metazoan life on Earth

“…Recent findings of multicellular organisms, cf. Franceville biota of 2.1 Ga (El Albani et al, 2010, Stirling biota of~1.8 Ga (Bengtson et al, 2017), Montana biota of 1.5-1.3 Ga (Zhu et al, 2016), and motile organisms from 2.1 Ga old rocks (El Albani et al, 2019), inspire a re-assessment of the Vindhyan metazoan records for the evolution of advanced life forms during Precambrian. Therefore, a detailed investigation with most advanced techniques is necessary to correctly assess the affinity of some of the problematic features within the Vindhyan succession.…”

“…The microbial record of Earth dates back to 3700 Ma (Nutman et al, 2016). However, the macroscopic fossil records of the Precambrian remain controversial (Han and Runnegar, 1992;Knoll et al, 2006;Seilacher, 2007;Bengtson et al, 2009;El Albani et al, 2010;Bengtson et al, 2017;El Albani et al, 2019). Microbes dominated the Precambrian atmosphere and microbial mat cover developed profusely on the seafloor.…”