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65-530: The Trezona Formation is a Neoproterozoic era fossiliferous geological formation in South Australia . This article about a specific stratigraphic formation is a stub . You can help Misplaced Pages by expanding it . Neoproterozoic The Neoproterozoic Era is the last of the three geologic eras of the Proterozoic eon , spanning from 1 billion to 538.8 million years ago, and

130-537: A basal metazoan but of unknown taxonomic placement, had been noted to have similarities with the Ediacaran fauna. It has since been found to be a siphonophore , possibly even sections of a more complex species. It took almost 4 billion years from the formation of the Earth for Ediacaran fossils to first appear, 655 million years ago. While putative fossils are reported from 3,460  million years ago ,

195-459: A nervous system and brains , meaning that "the path toward intelligent life was embarked upon more than once on this planet". In 2018 analysis of ancient sterols was taken as evidence that one of the period's most-prominent and iconic fossils, Dickinsonia , was an early animal. Since the most primitive eumetazoans —multi-cellular animals with tissues—are cnidarians , and the first recognized Ediacaran fossil Charnia looks very much like

260-399: A sea pen , the first attempt to categorise these fossils designated them as jellyfish and sea pens . However, more recent discoveries have established that many of the circular forms formerly considered "cnidarian medusa" are actually holdfasts – sand-filled vesicles occurring at the base of the stem of upright frond-like Ediacarans. A notable example is the form known as Charniodiscus ,

325-532: A characteristically wrinkled ("elephant skin") and tubercular texture. Some Ediacaran strata with the texture characteristics of microbial mats contain fossils, and Ediacaran fossils are almost always found in beds that contain these microbial mats. Although microbial mats were once widespread before the Cambrian substrate revolution , the evolution of grazing organisms vastly reduced their numbers. These communities are now limited to inhospitable refugia , such as

390-578: A circular impression later found to be attached to the long 'stem' of a frond-like organism that now bears the name. The link between frond-like Ediacarans and sea pens has been thrown into doubt by multiple lines of evidence; chiefly the derived nature of the most frond-like pennatulacean octocorals, their absence from the fossil record before the Tertiary, and the apparent cohesion between segments in Ediacaran frond-like organisms. Some researchers have suggested that an analysis of "growth poles" discredits

455-474: A factor; the same fossils are found at all palaeolatitudes (the latitude where the fossil was created, accounting for continental drift - an application of paleomagnetism ) and in separate sedimentary basins . An analysis of one of the White Sea fossil beds, where the layers cycle from continental seabed to inter-tidal to estuarine and back again a few times, found that a specific set of Ediacaran organisms

520-677: A few are preserved within sandy units. The Nama assemblage is best represented in Namibia . It is marked by extreme biotic turnover, with rates of extinction exceeding rates of origination for the whole period. Three-dimensional preservation is most common, with organisms preserved in sandy beds containing internal bedding. Dima Grazhdankin believes that these fossils represent burrowing organisms, while Guy Narbonne maintains they were surface dwellers. These beds are sandwiched between units comprising interbedded sandstones, siltstones and shales —with microbial mats, where present, usually containing

585-744: A million years after the Earth emerged from a global glaciation , suggesting that ice cover and cold oceans may have prevented the emergence of multicellular life. In early 2008, a team analysed the range of basic body structures ("disparity") of Ediacaran organisms from three different fossil beds: Avalon in Canada, 575  million years ago to 565  million years ago ; White Sea in Russia, 560  million years ago to 550  million years ago ; and Nama in Namibia, 550  million years ago to 542  million years ago , immediately before

650-639: A separate subkingdom level category Vendozoa (now renamed Vendobionta ) in the Linnaean hierarchy for the Ediacaran biota. If these enigmatic organisms left no descendants, their strange forms might be seen as a "failed experiment" in multicellular life, with later multicellular life evolving independently from unrelated single-celled organisms. A 2018 study confirmed that one of the period's most-prominent and iconic fossils, Dickinsonia , included cholesterol , suggesting affinities to animals, fungi, or red algae. The first Ediacaran fossils discovered were

715-535: A similarity to molluscs , and other organisms have been thought to possess bilateral symmetry , although this is controversial. Most macroscopic fossils are morphologically distinct from later life-forms: they resemble discs, tubes, mud-filled bags or quilted mattresses. Due to the difficulty of deducing evolutionary relationships among these organisms, some palaeontologists have suggested that these represent completely extinct lineages that do not resemble any living organism. Palaeontologist Adolf Seilacher proposed

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780-404: A variety of depositional conditions. Each formation is commonly grouped into three main types, known as assemblages and named after typical localities. Each assemblage tends to occupy its own time period and region of morphospace, and after an initial burst of diversification (or extinction) changes little for the rest of its existence. The Avalon assemblage is defined at Mistaken Point one

845-666: Is approximately 555 million years in age, roughly coeval with Ediacaran fossils of the Ediacara Hills in South Australia and the White Sea on the coast of Russia . While rare fossils that may represent survivors have been found as late as the Middle Cambrian (510–500 Mya), the earlier fossil communities disappear from the record at the end of the Ediacaran leaving only curious fragments of once-thriving ecosystems . Multiple hypotheses exist to explain

910-465: Is correct then this suggests that the biota had already had limited exposure to "predation". Increased competition due to the evolution of key innovations among other groups, perhaps as a response to predation, may have driven the Ediacaran biota from their niches. However, the supposed "competitive exclusion" of brachiopods by bivalve molluscs was eventually deemed to be a coincidental result of two unrelated trends. Great changes were happening at

975-504: Is not found in a restricted environment subject to unusual local conditions: they are global. The processes that were operating must therefore have been systemic and worldwide. Something about the Ediacaran Period permitted these delicate creatures to be left behind; the fossils may have been preserved by virtue of rapid covering by ash or sand, trapping them against the mud or microbial mats on which they lived. Their preservation

1040-836: Is the last era of the Precambrian "supereon". It is preceded by the Mesoproterozoic era and succeeded by the Paleozoic era of the Phanerozoic eon, and is further subdivided into three periods , the Tonian , Cryogenian and Ediacaran . One of the most severe glaciation event known in the geologic record occurred during the Cryogenian period of the Neoproterozoic, when global ice sheets may have reached

1105-493: The 610 million year old Twitya formation, and older rocks dating to 770  million years ago in Kazakhstan. On the early Earth, reactive elements, such as iron and uranium , existed in a reduced form that would react with any free oxygen produced by photosynthesising organisms. Oxygen would not be able to build up in the atmosphere until all the iron had rusted (producing banded iron formations ), and all

1170-721: The Mayanian (from 1000 to 850 Ma) followed by the Baikalian (from 850 to 650 Ma). The idea of the Neoproterozoic Era was introduced in the 1960s. Nineteenth-century paleontologists set the start of multicellular life at the first appearance of hard-shelled arthropods called trilobites and archeocyathid sponges at the beginning of the Cambrian Period. In the early 20th century, paleontologists started finding fossils of multicellular animals that predated

1235-484: The Avalon Peninsula of Canada, the oldest locality with a large quantity of Ediacaran fossils. The assemblage is easily dated because it contains many fine ash-beds, which are a good source of zircons used in the uranium-lead method of radiometric dating . These fine-grained ash beds also preserve exquisite detail. Constituents of this biota appear to survive through until the extinction of all Ediacarans at

1300-541: The Mistaken Point assemblage in Newfoundland changed all this as the delicate detail preserved by the fine ash allowed the description of features that were previously undiscernible. It was also the first discovery of Ediacarans in deep water sediments. Poor communication, combined with the difficulty in correlating globally distinct formations , led to a plethora of different names for the biota. In 1960

1365-674: The Vendian , while Chinese geologists referred to it as the Sinian , and most Australians and North Americans used the name Ediacaran. However, in 2004, the International Union of Geological Sciences ratified the Ediacaran Period to be a geological age of the Neoproterozoic, ranging from 635 to 538.8 (at the time to 542) million years ago. The Ediacaran Period boundaries are the only Precambrian boundaries defined by biologic Global Boundary Stratotype Section and Points , rather than

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1430-646: The bacterial precipitation of minerals formed a "death mask", ultimately leaving a positive, cast-like impression of the organism. The Ediacaran biota exhibited a vast range of morphological characteristics. Size ranged from millimetres to metres; complexity from "blob-like" to intricate; rigidity from sturdy and resistant to jelly-soft. Almost all forms of symmetry were present. These organisms differed from earlier, mainly microbial, fossils in having an organised, differentiated multicellular construction and centimetre-plus sizes. These disparate morphologies can be broadly grouped into form taxa : Classification of

1495-464: The equator and created a " Snowball Earth " lasting about 100 million years. The earliest fossils of complex life are found in the Tonian period in the form of Otavia , a primitive sponge , and the earliest fossil evidence of metazoan radiation are found in the Ediacaran period, which included the namesaked Ediacaran biota as well as the oldest definitive cnidarians and bilaterians in

1560-619: The stromatolites found in Hamelin Pool Marine Nature Reserve in Shark Bay , Western Australia , where the salt levels can be twice those of the surrounding sea. The preservation of Ediacaran fossils is of interest, since as soft-bodied organisms they would normally not fossilize. Further, unlike later soft-bodied fossil biota such as the Burgess Shale or Solnhofen Limestone , the Ediacaran biota

1625-473: The Cambrian could simply be due to conditions that no longer favoured the fossilisation of Ediacaran organisms, which may have continued to thrive unpreserved. However, if they were common, more than the occasional specimen might be expected in exceptionally preserved fossil assemblages (Konservat- Lagerstätten ) such as the Burgess Shale and Chengjiang . Although no reports of Ediacara-type organisms in

1690-570: The Cambrian period are widely accepted at present, a few disputed reports have been made, as well as unpublished observations of 'vendobiont' fossils from 535 Ma Orsten-type deposits in China. It has been suggested that by the Early Cambrian, organisms higher in the food chain caused the microbial mats to largely disappear. If these grazers first appeared as the Ediacaran biota started to decline, then it may suggest that they destabilised

1755-676: The Cambrian. A complex fauna was found in South West Africa in the 1920s but was inaccurately dated. Another fauna was found in South Australia in the 1940s, but it was not thoroughly examined until the late 1950s. Other possible early animal fossils were found in Russia, England, Canada, and elsewhere (see Ediacaran biota ). Some were determined to be pseudofossils , but others were revealed to be members of rather complex biotas that remain poorly understood. At least 25 regions worldwide have yielded metazoan fossils older than

1820-463: The Earth had thawed from the Cryogenian period's extensive glaciation . This biota largely disappeared with the rapid increase in biodiversity known as the Cambrian explosion . Most of the currently existing body plans of animals first appeared in the fossil record of the Cambrian rather than the Ediacaran. For macroorganisms, the Cambrian biota appears to have almost completely replaced

1885-465: The Ediacaran organisms represented a unique and extinct grouping of related forms descended from a common ancestor ( clade ) and created the kingdom Vendozoa, named after the now-obsolete Vendian era. He later excluded fossils identified as metazoans and relaunched the phylum "Vendobionta", which he described as "quilted" cnidarians lacking stinging cells . This absence precludes the current cnidarian method of feeding, so Seilacher suggested that

1950-700: The Ediacarans is difficult, and hence a variety of theories exist as to their placement on the tree of life. Martin Glaessner proposed in The Dawn of Animal Life (1984) that the Ediacaran biota were recognizable crown group members of modern phyla, but were unfamiliar because they had yet to evolve the characteristic features we use in modern classification. In 1998 Mark McMenamin claimed Ediacarans did not possess an embryonic stage, and thus could not be animals. He believed that they independently evolved

2015-621: The French name "Ediacarien" – after the Ediacara Hills – was added to the competing terms "Sinian" and "Vendian" for terminal-Precambrian rocks, and these names were also applied to the life-forms. "Ediacaran" and "Ediacarian" were subsequently applied to the epoch or period of geological time and its corresponding rocks. In March 2004, the International Union of Geological Sciences ended the inconsistency by formally naming

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2080-402: The Neoproterozoic (early Tonian), but physical evidence for such animal life is lacking. Possible keratose sponge fossils have been reported in reefs dated to c. 890 million years before the present, but remain unconfirmed. The nomenclature for the terminal period of the Neoproterozoic Era has been unstable. Russian and Nordic geologists referred to the last period of the Neoproterozoic as

2145-528: The Tonian, rifting commenced which broke Rodinia into a number of individual land masses. Possibly as a consequence of the low-latitude position of most continents, several large-scale glacial events occurred during the Neoproterozoic Era including the Sturtian and Marinoan glaciations of the Cryogenian Period. These glaciations are believed to have been so severe that there were ice sheets at

2210-549: The absolute Global Standard Stratigraphic Ages . Ediacaran biota The Ediacaran ( / ˌ iː d i ˈ æ k ər ə n / ; formerly Vendian ) biota is a taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period ( c.  635–538.8 Mya ). These were enigmatic tubular and frond-shaped, mostly sessile , organisms. Trace fossils of these organisms have been found worldwide, and represent

2275-530: The assemblage is often found in water too deep for photosynthesis. The White Sea or Ediacaran assemblage is named after Russia's White Sea or Australia's Ediacara Hills and is marked by much higher diversity than the Avalon or Nama assemblages. In Australia, they are typically found in red gypsiferous and calcareous paleosols formed on loess and flood deposits in an arid cool temperate paleoclimate. Most fossils are preserved as imprints in microbial beds, but

2340-465: The base of the Cambrian. One interpretation of the biota is as deep-sea-dwelling rangeomorphs such as Charnia , all of which share a fractal growth pattern. They were probably preserved in situ (without post-mortem transportation), although this point is not universally accepted. The assemblage, while less diverse than the White Sea or Nama assemblages, resembles Carboniferous suspension-feeding communities, which may suggest filter feeding as

2405-462: The classical Precambrian–Cambrian boundary (which is currently dated at 538.8  million years ago ). A few of the early animals appear possibly to be ancestors of modern animals. Most fall into ambiguous groups of frond-like organisms; discoids that might be holdfasts for stalked organisms ("medusoids"); mattress-like forms; small calcareous tubes; and armored animals of unknown provenance. These were most commonly known as Vendian biota until

2470-729: The detailed geological mapping of the British Geological Survey , there was no doubt these fossils sat in Precambrian rocks. Palaeontologist Martin Glaessner finally, in 1959, made the connection between this and the earlier finds and with a combination of improved dating of existing specimens and an injection of vigour into the search, many more instances were recognised. All specimens discovered until 1967 were in coarse-grained sandstone that prevented preservation of fine details, making interpretation difficult. S.B. Misra 's discovery of fossiliferous ash -beds at

2535-460: The disappearance of this biota, including preservation bias , a changing environment, the advent of predators and competition from other life-forms. A sampling, reported in 2018, of late Ediacaran strata across Baltica (< 560 Mya) suggests the flourishing of the organisms coincided with conditions of low overall productivity with a very high percentage produced by bacteria, which may have led to high concentrations of dissolved organic material in

2600-437: The disc-shaped Aspidella terranovica in 1868. Their discoverer, Scottish geologist Alexander Murray , found them useful aids for correlating the age of rocks around Newfoundland . However, since they lay below the "Primordial Strata" of the Cambrian that was then thought to contain the very first signs of animal life, a proposal four years after their discovery by Elkanah Billings that these simple forms represented fauna

2665-455: The earliest known complex multicellular organisms . The term "Ediacara biota" has received criticism from some scientists due to its alleged inconsistency, arbitrary exclusion of certain fossils, and inability to be precisely defined. The Ediacaran biota may have undergone evolutionary radiation in a proposed event called the Avalon explosion , 575  million years ago . This was after

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2730-451: The end of the Precambrian and the start of the Early Cambrian. The breakup of the supercontinents , rising sea levels (creating shallow, "life-friendly" seas), a nutrient crisis, fluctuations in atmospheric composition, including oxygen and carbon dioxide levels, and changes in ocean chemistry (promoting biomineralisation ) could all have played a part. Late Ediacaran macrofossils are recognized globally in at least 52 formations and

2795-522: The equator—a state known as the " Snowball Earth ". Neoproterozoic time is subdivided into the Tonian (1000–720 Ma), Cryogenian (720–635 Ma) and Ediacaran (635–538.8 Ma) periods. In the regional timescale of Russia, the Tonian and Cryogenian correspond to the Late Riphean ; the Ediacaran corresponds to the Early to middle Vendian. Russian geologists divide the Neoproterozoic of Siberia into

2860-651: The evidence as ambiguous and unconvincing, for instance noting that Dickinsonia fossils have been found on rippled surfaces (suggesting a marine environment), while trace fossils like Radulichnus could not have been caused by needle ice as Retallack has proposed. Ben Waggoner notes that the suggestion would place the root of the Cnidaria back from around 900 mya to between 1500 mya and 2000 mya, contradicting much other evidence. Matthew Nelsen, examining phylogenies of ascomycete fungi and chlorophyte algae (components of lichens), calibrated for time, finds no support for

2925-567: The first uncontroversial evidence for life is found 2,700  million years ago , and cells with nuclei certainly existed by 1,200  million years ago . It could be that no special explanation is required: the slow process of evolution simply required 4 billion years to accumulate the necessary adaptations. Indeed, there does seem to be a slow increase in the maximum level of complexity seen over this time, with more and more complex forms of life evolving as time progresses, with traces of earlier semi-complex life such as Nimbia , found in

2990-802: The formal naming of the Period, and are currently known as Ediacaran Period biota. Most were soft bodied. The relationships, if any, to modern forms are obscure. Some paleontologists relate many or most of these forms to modern animals. Others acknowledge a few possible or even likely relationships but feel that most of the Ediacaran forms are representatives of unknown animal types. In addition to Ediacaran biota, two other types of biota were discovered in China. The Doushantuo Formation (of Ediacaran age) preserves fossils of microscopic marine organisms in great detail. The Huainan biota (of late Tonian age) consists of small worm-shaped organisms. Molecular phylogeny suggests that animals may have emerged even earlier in

3055-516: The fossil record. According to Rino and co-workers, the sum of the continental crust formed in the Pan-African orogeny and the Grenville orogeny makes the Neoproterozoic the period of Earth's history that has produced most continental crust. At the onset of the Neoproterozoic the supercontinent Rodinia , which had assembled during the late Mesoproterozoic, straddled the equator. During

3120-484: The fossils. The environment is interpreted as sand bars formed at the mouth of a delta 's distributaries . Mattress-like vendobionts ( Ernietta , Pteridinium , Rangea ) in these sandstones form a very different assemblage from vermiform fossils ( Cloudina , Namacalathus ) of Ediacaran "wormworld" in marine dolomite of Namibia. Since they are globally distributed – described on all continents except Antarctica – geographical boundaries do not appear to be

3185-402: The hypothesis that lichens predated the vascular plants . Several classifications have been used to accommodate the Ediacaran biota at some point, from algae , to protozoans , to fungi to bacterial or microbial colonies, to hypothetical intermediates between plants and animals. A new extant genus discovered in 2014, Dendrogramma , which at the time of discovery appeared to be

3250-402: The microbial mats in a " Cambrian substrate revolution ", leading to displacement or detachment of the biota; or that the destruction of the microbial substrate destabilized the ecosystem, causing extinctions. Alternatively, skeletonized animals could have fed directly on the relatively undefended Ediacaran biota. However, if the interpretation of the Ediacaran age Kimberella as a grazer

3315-533: The oceans. Determining where Ediacaran organisms fit in the tree of life has proven challenging; it is not even established that most of them were animals, with suggestions that they were lichens (fungus-alga symbionts), algae , protists known as foraminifera , fungi or microbial colonies, or hypothetical intermediates between plants and animals. The morphology and habit of some taxa (e.g. Funisia dorothea ) suggest relationships to Porifera or Cnidaria (e.g. Auroralumina ). Kimberella may show

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3380-631: The organisms may have survived by symbiosis with photosynthetic or chemoautotrophic organisms. Mark McMenamin saw such feeding strategies as characteristic for the entire biota, and referred to the marine biota of this period as a "Garden of Ediacara". Greg Retallack has proposed that Ediacaran organisms were lichens . He argues that thin sections of Ediacaran fossils show lichen-like compartments and hypha -like wisps of ferruginized clay, and that Ediacaran fossils have been found in strata that he interprets as desert soils. The suggestion has been disputed by other scientists; some have described

3445-472: The organisms that dominated the Ediacaran fossil record, although relationships are still a matter of debate. The organisms of the Ediacaran Period first appeared around 600  million years ago and flourished until the cusp of the Cambrian 538.8  million years ago , when the characteristic communities of fossils vanished. A diverse Ediacaran community was discovered in 1995 in Sonora , Mexico, and

3510-502: The other reactive elements had been oxidised. Donald Canfield detected records of the first significant quantities of atmospheric oxygen just before the first Ediacaran fossils appeared – and the presence of atmospheric oxygen was soon heralded as a possible trigger for the Ediacaran radiation . Oxygen seems to have accumulated in two pulses; the rise of small, sessile (stationary) organisms seems to correlate with an early oxygenation event, with larger and mobile organisms appearing around

3575-429: The pennatulacean nature of Ediacaran fronds. Adolf Seilacher has suggested that in the Ediacaran, animals take over from giant protists as the dominant life form. The modern xenophyophores are giant single-celled protozoans found throughout the world's oceans, largely on the abyssal plain . Genomic evidence suggests that the xenophyophores are a specialised group of Foraminifera . Seilacher has suggested that

3640-419: The presence of colonies of microbes that secrete sticky fluids or otherwise bind the sediment particles. They appear to migrate upwards when covered by a thin layer of sediment but this is an illusion caused by the colony's growth; individuals do not, themselves, move. If too thick a layer of sediment is deposited before they can grow or reproduce through it, parts of the colony will die leaving behind fossils with

3705-428: The presence of widespread microbial mats probably aided preservation by stabilising their impressions in the sediment below. The rate of cementation of the overlying substrate relative to the rate of decomposition of the organism determines whether the top or bottom surface of an organism is preserved. Most disc-shaped fossils decomposed before the overlying sediment was cemented, whereupon ash or sand slumped in to fill

3770-499: The second pulse of oxygenation. However, the assumptions underlying the reconstruction of atmospheric composition have attracted some criticism, with widespread anoxia having little effect on life where it occurs in the Early Cambrian and the Cretaceous. Periods of intense cold have also been suggested as a barrier to the evolution of multicellular life. The earliest known embryos, from China's Doushantuo Formation , appear just

3835-415: The start of the Cambrian. They found that, while the White Sea assemblage had the most species, there was no significant difference in disparity between the three groups, and concluded that before the beginning of the Avalon timespan these organisms must have gone through their own evolutionary "explosion", which may have been similar to the famous Cambrian explosion . The paucity of Ediacaran fossils after

3900-524: The terminal period of the Neoproterozoic after the Australian locality. The term "Ediacaran biota" and similar ("Ediacara" / "Ediacaran" / "Ediacarian" / "Vendian" and "fauna" / "biota") has, at various times, been used in a geographic, stratigraphic, taphonomic, or biological sense, with the latter the most common in modern literature. Microbial mats are areas of sediment stabilised by

3965-538: The time believed to be Early Cambrian. It was not until the British discovery of the iconic Charnia that the Precambrian was seriously considered as containing life. This frond -shaped fossil was found in England's Charnwood Forest first by a 15 year-old girl in 1956 (Tina Negus, who was not believed ) and then the next year by a group of three schoolboys including 15 year-old Roger Mason . Due to

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4030-441: The void, leaving a cast of the organism's underside. Conversely, quilted fossils tended to decompose after the cementation of the overlying sediment; hence their upper surfaces are preserved. Their more resistant nature is reflected in the fact that, in rare occasions, quilted fossils are found within storm beds as the high-energy sedimentation did not destroy them as it would have the less-resistant discs. Further, in some cases,

4095-426: Was associated with each environment. However, while there is some delineation in organisms adapted to different environments, the three assemblages are more distinct temporally than paleoenvironmentally. Because of this, the three assemblages are often separated by temporal boundaries rather than environmental ones (timeline at right). As the Ediacaran biota represent an early stage in multicellular life's history, it

4160-509: Was dismissed by his peers. Instead, they were interpreted as gas escape structures or inorganic concretions . No similar structures elsewhere in the world were then known and the one-sided debate soon fell into obscurity. In 1933, Georg Gürich discovered specimens in Namibia but assigned them to the Cambrian Period. In 1946, Reg Sprigg noticed "jellyfishes" in the Ediacara Hills of Australia's Flinders Ranges , which were at

4225-507: Was possibly enhanced by the high concentration of silica in the oceans before silica-secreting organisms such as sponges and diatoms became prevalent. Ash beds provide more detail and can readily be dated to the nearest million years or better using radiometric dating . However, it is more common to find Ediacaran fossils under sandy beds deposited by storms or in turbidites formed by high-energy bottom-scraping ocean currents. Soft-bodied organisms today rarely fossilize during such events, but

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