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Sphaeromorph acritarchs and cell clusters from the Torridonian, NW Scotland. a, Leiosphaeridia crassa; TOR08-18/Glame Member, Applecross Formation. b, Acritarch similar to Trematoligotriletum emarginatum Tim. with irregular verrucate surface; TOR08-26/Allt na Beistre Member, Applecross Formation. c, Lophosphaeridium sp. enclosed in a thin membranous vesicle; TOR08-34/Diabaig Formation. d, Surface detail of inner cyst (Lophosphaeridium sp.) in c showing small, evenly distributed granae. e, Leiosphaeridia crassa exhibiting a median split; TOR08-45/Cailleach Head Formation. f, Ellipsoidal cyst with granular wall structure exhibiting a terminal circular pylome excystment feature (arrow); TOR08-34/Diabaig Formation. g, Coarsely corrugate vesicle with dense contents; TOR08-27/Diabaig Formation. h, Spherical ball of cells enclosed within a complex wall (thin section from phosphatic nodule, Diabaig Formation). i, Blunt ellipsoidal vesicle with a micro-reticulate wall; TOR08-46/Cailleach Head Formation. j, Detail of i (box), showing the reticulate wall texture. k, Cell cluster, similar to Synsphaeridium sp. Note included condensed organic ‘spots’ (arrows); TOR08-26/Allt na Beistre Member, Applecross Formation. Scale bars: 10 µm (a–c, e–i, k), 1 µm (d, j).
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The existence of a terrestrial Precambrian (more than 542 Myr ago) biota has been largely inferred from indirect chemical and geological evidence associated with palaeosols, the weathering of clay minerals and microbially induced sedimentary structures in siliciclastic sediments. Direct evidence of fossils within rocks of non-marine origin in the P...
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Citations
... Like in the previous unit, acritarchs present simple morphology, recorded by the Leiosphaeridia sp. and Lophosphaeridia sp. genera, which is consonant with other lacustrine examples in the world ( Horodyski, 1994 ;Arouri, 1999 ;Prave, 2002 ;Strother et al., 2011 ). The shallow lakes were able to lodge life for some periods, while the microbial mats would Table 1 Camaquã Basin facies and facies association. ...
... To explain the exceptionally low number of spores and pollen grains per gram sediment in the Solnhofen limestones, Fisk et al. (2018,2020) argued that the site of deposition was farther away from the place(s) of growth of the source vegetation than previously thought and was characterized by higher sedimentation rates as those indicated by Barthel (1978) and Viohl (1996). Similar structures were also described by Strother et al. (2011) as Leiosphaeridia/Synsphaeridium although the original diagnosis does not comprehend hexagonal structures as described by the authors as well. Microbial mats resembling the specimens described by Strother et al. (2011), as well as those presented here, have been described by Pacton et al. (2009Pacton et al. ( , 2011 It could be argued that sampling for palynological analyses has thus far focused on those fossiliferous horizons of the successions that have also been used to date and reconstruct the landscape and palaeoclimate signal of the most fossil-rich beds within the Solnhofen Archipelago. ...
... Similar structures were also described by Strother et al. (2011) as Leiosphaeridia/Synsphaeridium although the original diagnosis does not comprehend hexagonal structures as described by the authors as well. Microbial mats resembling the specimens described by Strother et al. (2011), as well as those presented here, have been described by Pacton et al. (2009Pacton et al. ( , 2011 It could be argued that sampling for palynological analyses has thus far focused on those fossiliferous horizons of the successions that have also been used to date and reconstruct the landscape and palaeoclimate signal of the most fossil-rich beds within the Solnhofen Archipelago. These intervals correspond to the fine-laminated limestones, which were deposited during periods of low energy and high microbial activity. ...
... Heterotrophic life forms survived better after the evolution of photosynthetic cyanobacteria and the earliest marine and freshwater algal mats about 2.460-2.426 Ga [1,2]. With photosynthesis, atmospheric oxygen levels rose, the ozone layer formed, and life flourished on Earth. ...
... In the earliest phase of organic evolution (approximately 3.5 billion years ago), life consisted primarily of microorganisms that lived within deep-sea hydrothermal vent precipitates (e.g., Schopf, 2006). Multicellular terrestrial life appeared about 2.4 billion years later (e.g., Strother et al., 2011). ...
The explanatory challenge of sentience is known as the “hard problem of consciousness”: How does subjective experience arise from physical objects and their relations? Despite some optimistic claims, the perennial struggle with this question shows little evidence of imminent resolution. In this article, I focus on the “why” rather than on the “how” of sentience. Specifically, why did sentience evolve in organic life-forms? From an evolutionary perspective, this question can be framed: “What adaptive problem(s) did organisms face in their evolutionary past and how were those challenges met? I argue that sentience was a critical component of the adaptive solution (i.e., adopting an agentic stance) to increasingly complex and unpredictable demands placed on vertebrates approximately 500 million years ago (the so-called Cambrian explosion). One consequence of taking an agentic stance is that it freed the organism from its neural moorings, positioning it within phenomenal space outside its brain.
... The ocean covers 70% of the Earth's surface and represents 99% of the habitable space on the planet by volume (Costanza 1999). Life has existed in the ocean for at least 3.7 billion years, over three times as long as on land (Pearce et al. 2018;Strother et al. 2011). This long evolutionary history has resulted in some 2.2 million existing eukaryotic marine species (estimates range from 0.3 to 10 million species), of which 230,000 are confirmed (Mora et al. 2011;Louca et al. 2019). ...
The ‘ocean genome’ is the foundation upon which all marine ecosystems rest and is defined here as the ensemble of genetic material present in all marine biodiversity, including both the physical genes and the information they encode. The dynamics of the ocean genome enable organisms to adapt to diverse ecological niches and changing environmental conditions. The ocean genome also determines the productivity and resilience of biological resources, including fisheries and aquaculture, which collectively support global food security, human well-being and a sustainable ocean economy.
... The presence of late Precambrian land microbial communities comprising cyanobacteria and other prokaryotes is thought to have facilitated the evolution of terrestrial eukaryotic microalgae and fungi (Knauth and Kennedy, 2009;Strother et al., 2011). Strother et al. (2011) presented evidence for the presence of diverse assemblages dated at least 1 Ga of nonmarine ("continental") microfossils interpreted as eukaryotes from shallow freshwater and possibly subaerial settings, although these fossils are not easily attributed to extant taxa. ...
... The presence of late Precambrian land microbial communities comprising cyanobacteria and other prokaryotes is thought to have facilitated the evolution of terrestrial eukaryotic microalgae and fungi (Knauth and Kennedy, 2009;Strother et al., 2011). Strother et al. (2011) presented evidence for the presence of diverse assemblages dated at least 1 Ga of nonmarine ("continental") microfossils interpreted as eukaryotes from shallow freshwater and possibly subaerial settings, although these fossils are not easily attributed to extant taxa. Time-tree analyses indicate that Streptophyta and Chlorophyta diverged by 1 Ga and that certain lineages of green algae whose modern species are terrestrial were present by the Cryogenian, several hundred million years before embryophytes (Lutzoni et al., 2018;Del Cortona et al., 2020). ...
Green plants, broadly defined as green algae and the land plants (together, Viridiplantae), constitute the primary eukaryotic lineage that successfully colonized Earth's emergent landscape. Members of various clades of green plants have independently made the transition from fully aquatic to subaerial habitats many times throughout Earth's history. The transition, from unicells or simple filaments to complex multicellular plant bodies with functionally differentiated tissues and organs, was accompanied by innovations built upon a genetic and phenotypic toolkit that have served aquatic green phototrophs successfully for at least a billion years. These innovations opened an enormous array of new, drier places to live on the planet and resulted in a huge diversity of land plants that have dominated terrestrial ecosystems over the past 500 million years. This review examines the greening of the land from several perspectives, from paleontology to phylogenomics, to water stress responses and the genetic toolkit shared by green algae and plants, to the genomic evolution of the sporophyte generation. We summarize advances on disparate fronts in elucidating this important event in the evolution of the biosphere and the lacunae in our understanding of it. We present the process not as a step-by-step advancement from primitive green cells to an inevitable success of embryophytes, but rather as a process of adaptations and exaptations that allowed multiple clades of green plants, with various combinations of morphological and physiological terrestrialized traits, to become diverse and successful inhabitants of the land habitats of Earth.
... However, several climate models have inferred the presence of an openwater belt in low latitudes 12,14-16 , thus providing a refugium for aerobic eukaryotes (Fig. 3b). Others have argued that cryoconite holes or cryoconite pans-where the accumulation of dust and soot reduced local albedo, facilitated heat absorption, and promoted ice meltingsupported supraglacial oligotrophic meltwater ecosystems for cyanobacteria and aerobic eukaryotes 10,48,49 (Fig. 3a). Furthermore, organic carbon isotopes (δ 13 C org ) and pyrite sulfur isotopes (δ 34 S py ) from Nantuo Formation diamictite and sandstone/siltstone/mudstone indicate the presence of active carbon and sulfur cycles during the Marinoan Ice Age 19 . ...
During the Marinoan Ice Age (ca. 654–635 Ma), one of the ‘Snowball Earth’ events in the Cryogenian Period, continental icesheets reached the tropical oceans. Oceanic refugia must have existed for aerobic marine eukaryotes to survive this event, as evidenced by benthic phototrophic macroalgae of the Songluo Biota preserved in black shales interbedded with glacial diamictites of the late Cryogenian Nantuo Formation in South China. However, the environmental conditions that allowed these organisms to thrive are poorly known. Here, we report carbon-nitrogen-iron geochemical data from the fossiliferous black shales and adjacent diamictites of the Nantuo Formation. Iron-speciation data document dysoxic-anoxic conditions in bottom waters, whereas nitrogen isotopes record aerobic nitrogen cycling perhaps in surface waters. These findings indicate that habitable open-ocean conditions were more extensive than previously thought, extending into mid-latitude coastal oceans and providing refugia for eukaryotic organisms during the waning stage of the Marinoan Ice Age.
... While multicellularity emerged at least 2 dozen times during the 2 billion years of Eukarya evolution [194,195], the oldest evidence of eukaryotes living in non-marine environments dates to the Proterozoic (Torridonian, 1.2-1.0 Bya), yet is associated to aquatic (freshwater) systems [196]. The oldest known Chlorophyta (a clade composed of algae that along with Streptophyta constitute the green plants [197]) is 1 billion years old [198]. ...
... Interestingly, the pairwise comparison also shows that certain gene families changed little from Chlorophyta to Embryophyta (white boxes), and additionally the presence of species-specific adaptations, which may reflect the involvement of repair processes on habitat stress responses that are unrelated to IR (e.g., drought/desiccation and heat stress). [196,[231][232][233] and phylogenetic inference [207][208][209]. (A). ...
... Curve 6 shows the changes in background radiation levels over time [188]. [196,[231][232][233] and phylogenetic inference [207][208][209]. (A). ...
In present times, the levels of ionizing radiation (IR) on the surface of Earth are relatively low, posing no high challenges for the survival of contemporary life forms. IR derives from natural sources and naturally occurring radioactive materials (NORM), the nuclear industry, medical applications, and as a result of radiation disasters or nuclear tests. In the current review, we discuss modern sources of radioactivity, its direct and indirect effects on different plant species, and the scope of the radiation protection of plants. We present an overview of the molecular mechanisms of radiation responses in plants, which leads to a tempting conjecture of the evolutionary role of IR as a limiting factor for land colonization and plant diversification rates. The hypothesis-driven analysis of available plant genomic data suggests an overall DNA repair gene families’ depletion in land plants compared to ancestral groups, which overlaps with a decrease in levels of radiation exposure on the surface of Earth millions of years ago. The potential contribution of chronic IR as an evolutionary factor in combination with other environmental factors is discussed.
... The earliest evidence of eukaryotes (complex cells with organelles) dates from 1850 Ma (Knoll et al., 2006), and multicellular organisms were already present by 1700 Ma (Bonner, 1998). Algae-like multicellular land plants are dated back to 1000 Ma (Strother et al., 2011). The Ediacaran biota, which includes the first complex life forms, appeared during an interval known as the Ediacaran period, between 635 and 541 Ma, marking the end of the Proterozoic ( Jun-Yuan et al., 2000). ...
Earth is ~ 4600 million years old. An immense time for human times scales. Since its formation, Earth has undergone many changes, including the formation of oceans, kick start of plate tectonics, climate changes, and the emergence of life. To study these past events, earth scientists have to rely on the observation of the geological record. Over the years, we have been able to organize geological time. This was not a trivial endeavor, and it was only possible due to the advances in stratigraphy and dating techniques. Today, we recognize that the history of the Earth can be divided into four major Eons: the Hadean, the Archean, the Proterozoic, and the Phanerozoic. This chapter introduces the story of geological time and chronostratigraphy and briefly describes the major events in the Earth's history.
... At its deepest phylogenetic level, our analyses suggest that the earliest eukaryotes inhabited non-marine habitats (Fig. 4) and not marine habitats as often assumed (for example, refs. [54][55][56]. While the fossil record for early eukaryotes is sparse and difficult to distinguish from prokaryotes, there is evidence for early eukaryotes in non-marine or low-salinity environments from at least 1 billion years ago 55 . ...
... [54][55][56]. While the fossil record for early eukaryotes is sparse and difficult to distinguish from prokaryotes, there is evidence for early eukaryotes in non-marine or low-salinity environments from at least 1 billion years ago 55 . Furthermore, other key early eukaryotic innovations, such as the origin of the plastid organelles, have been inferred to have occurred around 2 billion years ago in low-salinity habitats 57,58 . ...
The successful colonization of new habitats has played a fundamental role during the evolution of life. Salinity is one of the strongest barriers for organisms to cross, which has resulted in the evolution of distinct marine and non-marine (including both freshwater and soil) communities. Although microbes represent by far the vast majority of eukaryote diversity, the role of the salt barrier in shaping the diversity across the eukaryotic tree is poorly known. Traditional views suggest rare and ancient marine/non-marine transitions but this view is being challenged by the discovery of several recently transitioned lineages. Here, we investigate habitat evolution across the tree of eukaryotes using a unique set of taxon-rich phylogenies inferred from a combination of long-read and short-read environmental metabarcoding data spanning the ribosomal DNA operon. Our results show that, overall, marine and non-marine microbial communities are phylogenetically distinct but transitions have occurred in both directions in almost all major eukaryotic lineages, with hundreds of transition events detected. Some groups have experienced relatively high rates of transitions, most notably fungi for which crossing the salt barrier has probably been an important aspect of their successful diversification. At the deepest phylogenetic levels, ancestral habitat reconstruction analyses suggest that eukaryotes may have first evolved in non-marine habitats and that the two largest known eukaryotic assemblages (TSAR and Amorphea) arose in different habitats. Overall, our findings indicate that the salt barrier has played an important role during eukaryote evolution and provide a global perspective on habitat transitions in this domain of life.
