Microfossils are contained within black chert like the ones seen here.
Credit: Professor Erica V. Barlow. All Rights Reserved.
In that vast passage of time before the mythical "Creation Week" when 99.97% of Earth History occurred, some events that were highly significant for the evolution of life on Earth were happening. One of these was the Great Oxidation Event or GOE, which was to change the course of evolutionary history and put it on a trajectory that led to the evolution of multicellularity and to all the biodiversity of multicellular plants, fungi and animals that we see today.
The GOE happened when proliferating cyanobacteria, which had been evolving for a billion years or more, started using photosynthesis to create sugar from carbon dioxide, water and solar energy, and pollute the atmosphere with their toxic waste, oxygen. It was a major environmental change, causing Earth's first mass extinction. To anyone who understands the link between environmental change and evolution, it won't come as a surprise to learn that it was accompanied by a major evolutionary change in living organisms - the change from prokaryote to eukaryote cells.
What and when was the Great Oxidation Event in Earth's history, and what were its consequences for life on Earth? The Great Oxidation Event, often abbreviated as GOE, was a significant period in Earth's history during which there was a substantial increase in atmospheric oxygen levels. It is estimated to have occurred approximately 2.4 billion to 2.3 billion years ago, in the Proterozoic Eon, specifically during the Paleoproterozoic era. The consequences of the Great Oxidation Event for life on Earth were profound and multifaceted:The connection between the GOE and the evolution of eukaryotes is the conclusion from the work of a team of researchers the University of New South Wales, Kensington, New South Wales, Australia, Pennsylvania State University, University Park, Pennsylvania, USA and University of California at Los Angeles (UCLA), Los Angeles, California, USA, led by Professor Erica V. Barlow of the Australian Centre for Astrobiology, University of New South Wales and the Department of Geosciences and the Earth and Environmental Systems Institute, Pennsylvania State University. Their findings are published open access in the journal Geobiology.In summary, the Great Oxidation Event was a crucial turning point in Earth's history, as it dramatically altered the composition of the atmosphere, influenced the evolution of life, and set the stage for the development of complex, oxygen-dependent organisms. It also left a lasting geological and environmental record in the form of banded iron formations and other sedimentary deposits.
- Oxygen Increase:
The most obvious consequence of the Great Oxidation Event was the significant rise in atmospheric oxygen levels. Before this event, Earth's atmosphere had very little oxygen, primarily consisting of gases like carbon dioxide, methane, and water vapor. The increase in oxygen during the Great Oxidation Event marked a fundamental change in the Earth's atmosphere.- Transformation of Life:
The rise of atmospheric oxygen had a profound impact on the evolution of life on Earth. Early life forms were anaerobic, meaning they did not require oxygen and were, in many cases, harmed by its presence. As oxygen levels increased, these anaerobic organisms faced new challenges and had to adapt or find niches where oxygen levels were lower. The Great Oxidation Event triggered the selection and diversification of aerobic organisms that could thrive in oxygen-rich environments.- Emergence of Complex Life:
The increase in oxygen provided an opportunity for the evolution of more complex and energetically efficient life forms. This laid the groundwork for the eventual emergence of multicellular organisms and, ultimately, complex life forms such as animals. The rise of oxygen was a crucial step in the development of the Earth's biodiversity.- Environmental Changes:
The Great Oxidation Event had significant geological and environmental consequences. The oxygen reacted with certain minerals and dissolved in the oceans, leading to the formation of iron-rich sediments and banded iron formations (BIFs). It also caused the oxygenation of Earth's oceans, which impacted the distribution of elements and nutrients in marine ecosystems.- Impacts on Climate:
The rise in atmospheric oxygen had implications for the Earth's climate. It led to a reduction in greenhouse gases like methane, which is a potent greenhouse gas. This reduction in greenhouse gases likely contributed to cooling the planet and influencing the climate during the Proterozoic Eon.
What caused it?
The exact causes of the Great Oxidation Event (GOE) are still a subject of scientific research and debate, and there isn't a single, definitive explanation. Several factors and processes likely contributed to the rise in atmospheric oxygen during this time. Some of the leading hypotheses and contributing factors include:It's important to note that the rise of oxygen during the GOE was not a rapid event but occurred over hundreds of millions of years. The exact timing and duration of the event are still topics of research, and the interplay of these various factors likely influenced the rate of oxygen increase. While these factors contributed to the GOE, the precise sequence of events and the relative importance of each factor remain subjects of ongoing scientific investigation. Understanding the causes of the Great Oxidation Event is challenging due to the lack of direct geological evidence from that time, but scientists continue to study ancient rocks and fossils to piece together this critical period in Earth's history.
- Cyanobacteria:
Cyanobacteria, also known as blue-green algae, are photosynthetic microorganisms that played a crucial role in the GOE. These ancient organisms were among the first to evolve oxygenic photosynthesis, a process that releases oxygen as a byproduct. As cyanobacteria proliferated in Earth's oceans, they released significant amounts of oxygen into the atmosphere, contributing to the oxygen increase.- Formation of Oxygen Sinks:
Early in Earth's history, oxygen produced by photosynthetic organisms was initially consumed by various processes and reactions. For example, oxygen reacted with iron in the oceans to form iron-rich sediments and banded iron formations (BIFs). This sequestration of oxygen initially removed it from the atmosphere, but when all the free iron in the oceans was oxygenated, this process failed, and oxygen was able to accumulate in the atmosphere.- Weathering of Rocks:
Over time, the weathering of rocks on the Earth's surface also played a role in releasing oxygen. Chemical weathering processes can break down minerals containing iron and sulfur, leading to the release of oxygen. This oxygen contributed to the gradual buildup of atmospheric oxygen levels.- Absence of Oxygen Sinks:
Another critical factor in the GOE was the limited availability of oxygen sinks. Initially, there were few organisms that could effectively consume the rising oxygen levels, and the atmosphere was gradually saturated with oxygen. As a result, oxygen began to accumulate in the atmosphere.
Although it had been hypothesised, there was no direct fossil evidence to support the hypothesis, until the team discovered that microfossils found in rocks from Western Australia, more closely resemble algae than prokaryote cells when compared to modern organisms.
The Hamersley Range, a mountainous region of Western Australia, where researchers conducted their work.
Credit: Professor Erica V. Barlow . All Rights Reserved.
What we show is the first direct evidence linking the changing environment during the Great Oxidation Event with an increase in the complexity of life. This is something that’s been hypothesized, but there’s just such little fossil record that we haven’t been able to test it.
The microfossils have a remarkable similarity to a modern family called Volvocaceae. This hints at the fossil being possibly an early eukaryotic fossil. That’s a big claim, and something that needs more work, but it raises an exciting question that the community can build on and test.
Professor Erica V. Barlow, corresponding author
An affiliate research professor
Department of Geosciences
Pennsylvania State University, PA, USA.
An affiliate research professor
Department of Geosciences
Pennsylvania State University, PA, USA.
These specific fossils are remarkably well preserved, which allowed for the combined study of their morphology, composition, and complexity. The results provide a great window into a changing biosphere billions of years ago.
Professor Christopher H. House, co-author
Department of Geosciences and the Earth and Environmental Systems Institute
Pennsylvania State University, University Park, Pennsylvania, USA.
Department of Geosciences and the Earth and Environmental Systems Institute
Pennsylvania State University, University Park, Pennsylvania, USA.
Compared to modern organisms, Barlow said, the microfossils have explicit similarities with algal colonies, including in the shape, size and distribution of both the colony and individual cells and membranes around both cell and colony.
The findings have implications for both how long it took complex life to form on early Earth — the earliest, uncontroversial evidence of life is 3.5 billion years old — and what the search for life elsewhere in the solar system may reveal, the scientists said.
The findings have implications for both how long it took complex life to form on early Earth — the earliest, uncontroversial evidence of life is 3.5 billion years old — and what the search for life elsewhere in the solar system may reveal, the scientists said.
I think finding a fossil that is this relatively large and complex, relatively early on in the history of life on Earth, kind of makes you question — if we do find life elsewhere, it might not just be bacterial prokaryotic life. Maybe there’s a chance there could be something more complex preserved — even if it’s still microscopic, it could be something of a slightly higher order.
Professor Erica V. Barlow.
How does an analysis of the carbon isotopic content of a microfossil show its biogenicity? The analysis of carbon isotopic content in a microfossil can provide important clues about its biogenicity, which means whether the microfossil is of biological origin or not. This is achieved by examining the ratios of stable carbon isotopes, specifically carbon-12 (12C) and carbon-13 (13C), in the microfossil's organic material. Here's how it works:The abstract and introduction to the team's paper in Geobiology gives more technical details:By analyzing the carbon isotopic content of microfossils, scientists can gain insights into the type of organisms that produced them, their metabolic pathways, and the environmental conditions in which they lived. This information is valuable for understanding ancient ecosystems, evolutionary history, and environmental changes through geological time. It can also help in distinguishing between biological and non-biological structures in the fossil record.
- Fractionation During Photosynthesis: In photosynthesis, plants and photosynthetic microorganisms preferentially take up carbon dioxide (CO2) containing the lighter isotope, carbon-12 (12C). This preference leads to a natural enrichment of 12C in their organic material. The organic compounds produced through photosynthesis, such as carbohydrates and lipids, tend to have lower ratios of 13C to 12C (denoted as δ13C values) compared to the carbon dioxide in the atmosphere.
- Distinctive Isotopic Signatures: Biogenic materials like plants and phytoplankton have distinctive isotopic signatures with lower δ13C values due to this fractionation during photosynthesis. The specific δ13C values can vary depending on the type of photosynthetic organism, environmental conditions, and other factors.
- Comparison with Inorganic Carbon: In contrast, non-biogenic carbon, such as carbonates and some mineral forms of carbon, has different δ13C values. These inorganic forms typically have higher δ13C values since they are not subject to the fractionation effects associated with photosynthesis.
- Identifying Biogenicity: To determine the biogenicity of a microfossil, researchers compare the δ13C values of the organic material within the microfossil to the expected values for biogenic carbon. If the δ13C values of the microfossil match those of biogenic materials, it suggests a biological origin. Conversely, if the δ13C values are significantly different and more closely resemble inorganic carbon, it indicates a non-biogenic origin.
Would that work on a 2.4-billion-year-old microfossil?
Analyzing the carbon isotopic content of a 2.4-billion-year-old microfossil from the Precambrian eon can still provide insights into its potential biogenicity. While the preservation of microfossils of this age can be challenging due to the effects of diagenesis and metamorphism, certain characteristics of the carbon isotopic signature can still be informative. Here's how it might work:It's important to note that the farther back in time we go in the geological record, the more challenging it becomes to confidently determine biogenicity. Geological processes, including metamorphism and alteration, can significantly affect the preservation of ancient microfossils and their carbon isotopic signatures. In some cases, it may be difficult to definitively establish the biogenicity of a 2.4-billion-year-old microfossil, and researchers often employ multiple analytical techniques and approaches to build a robust case for their interpretation.
- Comparison to Surrounding Minerals: In Precambrian microfossils, especially those that have experienced significant geological alteration, the carbon isotopic ratios of the microfossil's organic material can be compared to the isotopic compositions of surrounding minerals. If the microfossil's carbon isotopic signature is distinct from the minerals and is more in line with the expected isotopic ratios for biogenic carbon, it suggests biogenicity.
- Multiple Lines of Evidence: The carbon isotopic analysis should ideally be complemented by other lines of evidence, such as the microfossil's morphology, chemical composition, and the geological context in which it is found. If these other factors also support a biogenic interpretation, it strengthens the case for the microfossil's biogenicity.
- Relative Isotopic Ratios: Even in the presence of diagenesis and metamorphism, the relative isotopic ratios of carbon isotopes (δ13C values) within the microfossil can provide information. If the δ13C values are consistent with the expected fractionation patterns associated with photosynthesis, it supports the possibility of a biological origin.
While carbon isotopic analysis is a valuable tool, it is just one piece of the puzzle in the study of ancient microfossils and their biogenicity, especially in the challenging geological conditions of the Precambrian eon.
AbstractOf course, you won't find any mention of single-cell organisms, either prokaryotes or eukaryotes, in creationism's favourite science 'textbook', the Bible, for the simple reason that the authors had not the slightest inkling that they existed. Just as they were in complete ignorance of the vast passage of time that had passed since Earth formed around the sun, and knew even less, if that were possible, about how long the Universe had really existed, so they were ignorant of the process of evolution and made up stories to fill the gaps in their knowledge.
The great oxidation event (GOE), ~2.4 billion years ago, caused fundamental changes to the chemistry of Earth's surface environments. However, the effect of these changes on the biosphere is unknown, due to a worldwide lack of well-preserved fossils from this time. Here, we investigate exceptionally preserved, large spherical aggregate (SA) microfossils permineralised in chert from the c. 2.4 Ga Turee Creek Group in Western Australia. Field and petrographic observations, Raman spectroscopic mapping, and in situ carbon isotopic analyses uncover insights into the morphology, habitat, reproduction and metabolism of this unusual form, whose distinctive, SA morphology has no known counterpart in the fossil record. Comparative analysis with microfossils from before the GOE reveals the large SA microfossils represent a step-up in cellular organisation. Morphological comparison to extant micro-organisms indicates the SAs have more in common with coenobial algae than coccoidal bacteria, emphasising the complexity of this microfossil form. The remarkable preservation here provides a unique window into the biosphere, revealing an increase in the complexity of life coinciding with the GOE.
1 INTRODUCTION
The great oxidation event (GOE), ~2.4 billion years ago, represents an irreversible shift in atmospheric composition that dramatically altered weathering and nutrient cycles on the early Earth. Yet little is known about the effect of this change on the biosphere, as there is a worldwide scarcity of well-preserved fossiliferous rocks from this time period.
A well-preserved fossil deposit from this time period has recently been recognised within the lower part of the c. 2.4 Ga Turee Creek Group (TCG) in Western Australia. Work on this deposit has so far revealed a microbialite reef complex containing an assortment of very well-preserved macroscopic and microscopic fossils that provide unique insight into the diversity of life during the GOE (Barlow et al., 2016; Barlow & Van Kranendonk, 2018; Fadel et al.,2017; Nomchong & Van Kranendonk, 2020; Schopf et al., 2015). In particular, the appearance of the oldest known thrombolites and sideways branching stromatolites (Barlow et al., 2016; Nomchong & Van Kranendonk, 2020), two new microfossil forms (Barlow & Van Kranendonk, 2018) and the oldest known phosphorite (Soares et al., 2019), point to a link between the diversification of life and the rise of atmospheric oxygen.
Here, we provide a detailed morphological description and in situ carbon isotopic analyses of one of the new microfossil forms: a large spherical aggregate (SA) permineralised within nodular black chert (NBC). We combine field, petrographic and in situ carbon isotopic data to confirm the biogenicity of this unique fossil occurrence. We then interpret aspects of the SA microfossil morphology, assess its likely habitat and investigate its possible metabolism and reproduction. The remarkable preservation of the studied material reveals the SA microfossils constitute a form of cellular organisation previously unseen in rocks of this age, suggesting a possible link between the GOE and the development of more complex life.
Figure 1. 
Archetypal large spherical aggregate (SA) microfossils with wide, kerogen-free surrounding rinds. Microfossil shape is most commonly spherical, with radial symmetry. All images are vertical cross sections through bedding. (a) Plane polarised light (PPL) image of slightly ellipsoidal SAs oriented with long axes perpendicular to bedding; note the even width of rinds. Dense, bedded organic matter (OM) that directly underlies the left SA appears to be deflected downwards, around the SA and its surrounding rind (arrow). (b, c) and (d, e) show specimens in both PPL and cross polarised light (XPL), highlighting the very fine microquartz grainsize within the rinds (arrow in e). Carbonate rhombs are occasionally observed intruding into microfossil rinds; these are visible in a (left SA, right side of rind), in b, c (left side of rind), and in e (right side of rind)
Figure 2. 
SA microfossils appear as individual specimens of consistent size and shape and are occasionally observed in relatively close proximity. The main organic ‘body’ of the SAs has an irregular edge, with thin, wispy, wire-like structures that extend out into the clear surrounding rind (most clearly visible in c). Note the transparent calcite rhombs poking into the SA rinds in (b) and (e). Arrow in (d) highlights deformed OM that bends around the underside of the SA; note the SA rind here is uneven (thin on the underside and thick on the topside; see also Figure S7d). All images are vertical cross sections through bedding in PPL, taken from thick (~100 μm) petrographic sections. The thickness of the section combined with the density of surrounding OM obscures the SA rind in places.
Figure 3. In thinner (~30 μm thick) petrographic sections, SA microfossils are more transparent, revealing an internal framework of honeycomb-like compartments. The compartments are sub-spherical to polygonal in shape and are composed of dark brown, often granular, OM. (a) SA specimen with a hollow core and an even rind that is partially outlined along the outer, top edge. Inset shows enlarged view of thin, wispy structures emanating out from the SA body into the surrounding rind. (b-h) Variably preserved SA microfossils and surrounding rinds. Arrow in (d) points to deflected underlying bedding (see also Figure S7). Fragments of thick filamentous microfossils are visible in (f) and (h). The line in (g) that cuts diagonally across the image is the broken edge of the thin section. All images are vertical cross sections through bedding in PPL.
Figure 5. Well-preserved SA microfossils contain amber brown-coloured cell-like spheres within the honeycomb-like compartments. (a, b) Dense, opaque SA specimen in PPL (a) and XPL (b). Part b shows the fine-grained microquartz that preserves the SA. (c-e) Same specimen as a/b imaged under higher magnification and overexposed to more clearly show the internal structure (d and e are taken in the same x/y position but at different focal depths). Note the darker, more granular nature of the honeycomb-like compartments that surround the cell-like spheres. (f) Another opaque SA specimen in PPL; note the thin wispy structures that extend out into the kerogen-free rind. (g) Same specimen as in f, overexposed to show it is composed of tightly packed cell-like spheres that are distinct from the honeycomb-like framework. Note the clear central domains within the cell-like spheres in (d), (e) and (g).
Figure 6. Internal structure of the SA microfossils, continued. (a, b) Opaque SA microfossil in PPL (a) and XPL (b), highlighting the consistent size of the microquartz preserving the microfossil. (c-g) Higher magnification images in PPL of same specimen as in a/b; Images are overexposed to show internal detail more clearly. Parts (c) and (d) are taken in the same x/y position but at different focal depths, highlighting the tightly packed cell-like spheres contained within the SA. Part (e) is detail of boxed area in (c), showing what appear to be multiple, smaller cell-like spheres contained within one compartment. At least five cell-like spheres are visible, and these are ~3.5 to 4 μm in diameter. Parts (f) and (g) show detail of boxed areas in (d), indicating the spherical nature of the cell-like spheres (f) and that they appear to be separate from the OM of the surrounding compartments (arrow in g). (h-j) Confocal laser scanning microscope (CLSM) images of SA microfossils. Note the clear rind visible in (h), and the spherical to polygonal compartments in (j) (arrow). Also note the clearer central domains within the cell-like spheres (visible in c, f, g, j). Parts (a), (h), (i) and (j) are of different specimens.
Figure 8. Examples of extracellular mucilage in an extant micro-organism, Asterococcus (a) and a fossilised micro-organism, Eogloeocapsa avzyanica (b). Note how the mucilage in both examples creates a clear, wide boundary around the cells that keeps the surrounding matrix material at bay. (c, d) ‘Polyhedral packing morphology’ in colonial micro-organisms: extant form Gloeothece (c) and sketch of extant form Gloeocapsa (d), showing tightly packed cells results in the cell envelope shape varying from spherical to pentagonal. Images from: (a) Matthews (2016.1); (b) Sergeev (1994); and (c, d) Golubic and Barghoorn (1977).
Figure 9. Comparison between the Turee Creek Group SA microfossils and younger fossilised micro-organisms that contain some broadly similar morphological features. (a) Pleurocapsa-like microfossil from the Neoproterozoic Hector Formation (image from Moorman, 1974). (b) Chroococcoid cyanobacterial microfossil from the Late Mesoproterozoic Avzyan Formation (image from Sergeev, 1994). (c) An acritarch, Timofeevia, from the Cambrian McMullin Formation (image from Palacios et al., 2012). (d) Megasphaera minuscula microfossil preserved in phosphorite from the Ediacaran upper Khesen Formation (red box is from original image used in Anderson et al., 2019.1). (e, f) The large spherical aggregate microfossils studied here. (a1-f1) Schematic drawings of the microfossils in parts (a-f), resized to be shown at the same scale as one another to highlight the colossal differences in size. Note that the specimen in (e) is overexposed to show its internal structure more clearly, but that this removes detail of the outside of the SA microfossil, meaning the overall size of this specimen is larger than depicted in (e). For the comparative size diagram in (e1), the full size of this specimen (see Figure 5a) has been used.
Figure 10. Direct comparison of Turee Creek Group SA microfossils (a, c) and extant, Volvocacean coenobial algae (Eudorina; b, d). Note similarities in symmetrical shape, structure and overall size. Spherical (a) and ellipsoidal (c) microfossils with wide, kerogen-free rinds; PPL. Compare with spherical (b) and ellipsoidal (d) coenobia that are surrounded by thick, clear, extracellular mucilage. Also note the thin, wire-like structures and apparent hollow centre of the microfossil in part (c) (and the hint of a hollow centre within the specimen in part a) and compare with the flagella and hollow centre of the coenobia in parts (b) and (d). Image credit: (b) Matthews (2016.1) and (d) Antonio Guillén.
Figure 11. Direct comparison of Turee Creek Group SA microfossils (a, c, e) with illustrations of extant, Volvocacean coenobial algae (Eudorina; b, d, f). Note overall similarities in size, shape and structure. (a) CLSM image of a SA microfossil highlighting the interconnected nature of the spherical, honeycomb-like compartments. Compare with sketch of Eudorina coenobium (b), where spherical cells are individually surrounded by spherical sheaths that are interconnected with neighbouring sheaths. (c) Large (~137 μm diameter) SA microfossil with pentagonal to hexagonal compartments that enclose tightly packed, cell-like spheres; PPL. Note the clear, central domains within the middle of each sphere (also visible in parts a and e). Compare with sketch of Eudorina coenobium (d), where tightly packed cells (containing round, central pyrenoids) are individually surrounded by slightly irregular, hexagonal sheaths. (e) SA specimen that contains multiple, smaller cell-like spheres within one compartment (red arrow). Compare with sketch of Eudorina coenobium (f), showing asynchronous daughter colony formation during asexual reproduction. Note the similarities in size between the small cell-like spheres in the microfossil (red arrow in part e) and the daughter cells in the extant coenobium (black arrow in part f). Sketch credit: (a) Prescott (1955) and (d, f) Menezes and Bicudo (2008). Scale in part (b) is estimated from reported diameter (89 μm) of sketched colony.Barlow, E. V., House, C. H., Liu, M.-C., Wetherington, M. T., & Van Kranendonk, M. J. (2023).
Distinctive microfossil supports early Paleoproterozoic rise in complex cellular organisation.
Geobiology, 00, 1-23. https://doi.org/10.1111/gbi.12576
Copyright: © 2023 The authors.
Published by John Wiley & Sons Ltd. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
The result illustrates the difference between ignorant guesswork and intuition and meticulous scientific investigation and logical deduction from the position of knowledge.
The former has a small flat Earth with a dome over it being created by magic just 10,000 years ago, whilst the latter reveals the magnificent truth of the origins of living species on an old Earth in a much older Universe.
The former has followers who are required to be intellectually dishonest, pretend to know things they don't know and pose as experts from a position of ignorance; the latter has followers who have the intellectual and personal integrity to readily admit what they don't know and treat ignorance as a spur to investigation and learning.
The former comes from a position of fear, the terror of learning and being wrong, to unreasonable certainty and arrogantly pompous self-importance; the latter gives rise the humility to accept that opinions are subordinate to facts in the quest for understanding, the joy of finding things out, the deep satisfaction of reasonable uncertainty and the anticipation of discovering more.
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