Life: the first two billion years

Knoll, Andrew H.; Bergmann, Kristin; Strauss, Justin V.

doi:10.1098/rstb.2015.0493

Cited by 120 publications

(99 citation statements)

References 145 publications

(204 reference statements)

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“…Putative microfossils have also been reported from the Strelley Pool cherts, as well as from cherts of the 3481 ± 3.6–Ma Dresser Formation ( 15 – 17 ); however, their interpretation remains controversial because simple biological remains can be difficult to distinguish from textures imparted during later hydrothermal alteration ( 18 – 20 ). More compelling, widespread and consistent 13 C depletion in organic matter from these and younger Warrawoona units is parsimoniously interpreted in terms of photoautotrophy ( 21 ).…”

Section: Constraining the Timing Of Major Evolutionary Eventsmentioning

confidence: 99%

The timetable of evolution

2017

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Section: Constraining the Timing Of Major Evolutionary Eventsmentioning

confidence: 99%

The timetable of evolution

2017

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“…If cyanobacteria had yet to appear, what made them? There is clear and multiple, independent lines of evidence that the Earth’s oceans and atmosphere were anoxic for roughly half its history, that is, until 2.4 Gyr (Knoll et al, 2016). Oxygen-evolving photosynthesis then emerged from anoxygenic photosynthesis with the advent of cyanobacteria – the only oxygenic phototrophic prokaryotes (Schopf, 2011).…”

Section: The Problem: Stromatolites a Billion Years Before The Cyanobmentioning

confidence: 99%

A Proposal for Formation of Archaean Stromatolites before the Advent of Oxygenic Photosynthesis

Allen

2016

Front. Microbiol.

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Stromatolites are solid, laminar structures of biological origin. Living examples are sparsely distributed and formed by cyanobacteria, which are oxygenic phototrophs. However, stromatolites were abundant between 3.4 and 2.4 Gyr, prior to the advent of cyanobacteria and oxygenic photosynthesis. Here I propose that many Archaean stromatolites were seeded at points of efflux of hydrogen sulfide from hydrothermal fields into shallow water, while their laminar composition arose from alternating modes of strictly anoxygenic photosynthetic metabolism. These changes were a redox regulatory response of gene expression to changing hydrogen sulfide concentration, which fluctuated with intermittent dilution by tidal action or by rainfall into surface waters. The proposed redox switch between modes of metabolism deposited sequential microbial mats. These mats gave rise to alternating carbonate sediments predicted to retain evidence of their origin in differing ratios of isotopes of carbon and sulfur and in organic content. The mats may have arisen either by replacement of microbial populations or by continuous lineages of protocyanobacteria in which a redox genetic switch selected between Types I and II photosynthetic reaction centers, and thus between photolithoautotrophic and photoorganoheterotrophic metabolism. In the latter case, and by 2.4 Gyr at the latest, a mutation had disabled the redox genetic switch to give simultaneous constitutive expression of both Types I and II reaction centers, and thus to the ability to extract electrons from manganese and then water. By this simple step, the first cyanobacterium had the dramatic advantage of emancipation from limiting supplies of inorganic electron donors, produced free molecular oxygen as a waste product, and initiated the Great Oxidation Event in Earth’s history at the transition from the Archaean to the Paleoproterozoic.

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“…The first session opened with an in-depth consideration by Knoll [1] (Harvard University and MIT, USA) on life 2 billion years ago, discussing the presence of bacteria in stromatolites and other sedimentary rocks. The first billion years of biological and environmental evolution featured bacteria and archaea living in oceans with much iron, but little oxygen.…”

Section: Sb 0000-0003-2148-1758mentioning

confidence: 99%