Did Ediacaran NeoProterozoic Kotlinian Mass Extinction Pave way for the Cambrian Explosion?

Ediacaran biota in the aftermath of the Kotlinian Crisis: Asha Group of the South Urals

Authors:

Kolesnikov et al

Abstract:

The Asha Group of the South Urals is dominated by laminated shales and thin siltstone–sandstone alternations interpreted as a prograding low-energy inner shelf depositional system. The succession includes several thick sharp-based sandstone bodies comprising interstratified fine- to medium-grained fine-laminated, planar-laminated, hummocky-, convolute- and wave-bedded, planar and trough cross-bedded sandstones, occasionally pebble- to boulder conglomerates, regarded as tidal, deltaic and shoreface depositional systems. The sandstone shoreface bodies are interpreted as forced-regressive deposits stranded in offshore positions during subsequent transgressions. Although palaeoecological and taphonomic context of the Asha Group is favourable for the Ediacara-type biofacies, the associated fossil assemblages nevertheless are depauperate and consist of frondomorph holdfast structures, palaeopascichnids, microbial colonies, arumberiamorph structures, as well as lithified microbial substrates (shagreen texture, biolaminites). In terms of fidelity and fossil completeness, preservation of Ediacaran fossils in the Asha Group is by no means inferior to that seen in other Ediacaran macrofossil localities. The low biodiversity of Ediacaran macrofossils can be attributed to a relatively young Ediacaran age of the Asha Group, which is constrained by a U–Pb zircon date of 547.6 ± 3.8 Ma from an ash bed in the lower part of the sedimentary succession. The uppermost part of the Asha Group has yielded bilobed burrows with a backfill structure suggesting an affinity with the ichnogenus Didymaulichnus from the Ediacaran–Cambrian boundary strata. The Asha Group therefore offers an important glimpse into the history of the Edacaran biota in the aftermath of the Kotlinian Crisis that caused extinction of dickinsoniomorphs, tribrachiomorphs and bilateralomorphs in wave- and current-agitated shoreface depositional systems ∼550 million years ago, but did not significantly affect frondomorphs and palaeopascichnids.

Evidence of the PaleoEnvironment of the Ediacaran From Brazil

Redox variations and bioproductivity in the Ediacaran: Evidence from inorganic and organic geochemistry of the Corumbá Group, Brazil

Authors:

1. Jorge E. Spangenberg (a)
2. Mariluz Bagnoud-Velásquez (a, b)
3. Paulo C. Boggiani (c)
4. Claudio Gaucher (d)

Affiliations:

a. Institute of Earth Sciences, University of Lausanne, 1015 Lausanne, Switzerland

b. Environmental Engineering Institute, EPFL EMAC, CH B2 397, 1015 Lausanne, Switzerland

c. Instituto de Geociências, Universidade de São Paulo, Rua do lago 562, São Paulo, SP, Brazil

d. Departamento de Geología, Facultad de Ciencias, Iguá 4225, 11400 Montevideo, Uruguay


Abstract:

Stable isotope ratios combined with elemental compositions and molecular biomass data provide a powerful tool in Neoproterozoic palaeoenvironmental interpretations. Here, we report the results of an extensive organic and inorganic geochemical study performed in the Ediacaran sedimentary succession of the Corumbá Group (CG) from SW-Brazil, deposited in a shallow marine basin in southwestern Gondwana. This sedimentary succession and in particular the Tamengo Formation, a unit bearing metazoan fossils, has been investigated by means of stable isotopes from carbonates (δ13Ccar and δ18O) and associated organic matter (δ13Cker and δ15Nker) together with hydrocarbon distribution and concentrations of major, trace and rare earth elements (REE). A short, post-glacial 13Ccar negative excursion, interpreted as a period of water mixing, is recorded in the cap carbonates overlying diamictites of the Puga Formation, related to Gaskiers or end-Cryogenian glaciation. The Tamengo Formation by contrast, represents a return to redox-stratified conditions in the basin. Two distinct biogeochemical modes alternate during deposition of Tamengo sediments: 1) An eutrophic, redox-stratified basin well defined by carbonaceous marls from the middle part of the unit but also recorded upwards, at the transition between bioclastic limestones and calcisiltites. 2) An anoxic basin well characterized in the shallow facies, particularly by bioclastic limestones of the upper Tamengo Formation. A positive Δ13Ccarb-ker (Δ13Ccar-ker = δ13Ccar – δ13Cker) excursion of ~ 5‰ in the carbonaceous marls is explained by enhanced primary productivity in surface waters probably related to an increase of pCO2, nutrients supply and possibly also changes of the primary producer communities. Abundant pyrite, a biomarker distribution characterized by the occurrence of gammacerane and a low Pr/Ph ratio (~ 0.7) are also remarkable signatures of these facies, most probably associated with a sulphate-reducing microbial consortium in an anoxic and sulfidic (euxinic) environment. However, low concentrations in redox-sensitive trace elements in these facies suggest a largely oxygenated water column, thus constraining the euxinic setting to the sediments and/or bottom waters. The shallow-water bioclastic limestones record higher concentrations of redox-sensitive elements and ∑ REE as well as a positive Ce anomaly supporting reducing conditions. Oxygenated conditions and dominance of eukaryotic algae characterize the overlying Guaicurus Formation. Principal component analysis (PCA) was used to assess the major geochemical associations. The most significant component combines parameters involved in primary production, such as P concentrations and 13Cker values. The bio-chemostratigraphic variations in this part of SW-Gondwana point to a stratified ocean with oxic surface waters alternating periods of high and low bioproductivity and anaerobic conditions at the bottom waters, in the aftermath of younger Neoproterozoic glaciations and close to the Precambrian-Cambrian boundary.

The Origin and Diversification of Animals

Birth and early evolution of metazoans

Authors:

1. Degan Shu (a)
2. Yukio Isozaki (b)
3. Xingliang Zhang (a)
4. Jan Han (a)
5. Shigenori Maruyama (c)

Affiliations:

a. Early Life Institute and State Key Laboratory of Continental Dynamics, Northwest University, Xi’an 710069, P.R. China

b. Department of Earth Science and Astronomy, University of Tokyo, Tokyo 153-8902, Japan

c. Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo 152-1551, Japan

Abstract:

The reconstruction of the phylogenetic tree of animals (TOA) has long been one of the central interests in biological and paleobiological sciences. We review the latest results of paleontological and stratigraphical studies on the Ediacaran-Cambrian sequences mainly from South China for revising the TOA in accordance with modern genome biology. A particular focus is given to the pattern of animal diversification based on the fossil first appearances of high-rank clades chiefly in phylum-level. The results show an abrupt divergence of lineages during the Ediacaran-Cambrian transition; however, the appearances of metazoan phyla were obviously diachronous, with three major phases recognized herein. The first phase is marked by the appearances of basal metazoan phyla in the latest Ediacaran. Very few unequivocal bilaterian clades were present at this phase. The second phase occurred in the Terreneuvian (Cambrian Stages 1-2), represented by the occurrences of many lophotrochozoan lineages. This phase also involves the appearances of calcified basal metazoan lineages, and possibly, those of contentious ecdysozoans in the latest Terreneuvian, but no deuterostome has been known from this age. The third and also the largest phase occurred in the Cambrian Stage 3, which involve all the three supraphylogenetic clades of the Eubilateria. A number of lophotrochozoan lineages, the bulk of ecdysozoans, and all deuterostome phyla, appeared for the first time in this phase. Since there is no unambiguous evidence for bilaterians in the Ediacaran, the Cambrian explosion sensu stricto was an abrupt diversification of bilateral lineages in a short time of ca. 25 million years across the Ediacaran-Cambrian boundary. Next critical issues in research include high-resolution chrono- and chemostratigraphic analyses, correlations between biotic events and environmental perturbations, physiological approach to the biological connotation of biomineralization, and exploration for the lost mid-oceanic biota and environments, which are crucial in understanding the entire picture of the Cambrian explosion.

Evidence of Massive Cyanobacterial Blooms in the Ediacarian

Terminal Proterozoic cyanobacterial blooms and phosphogenesis documented by the Doushantuo granular phosphorites I: In situ micro-analysis of textures and composition

Authors:

1. Zhenbing She (a, b)
2. Paul Strother (c)
3. Gregory McMahon (d)
4. Larry R. Nittler (e)
5. Jianhua Wang (e)
6. Jianhua Zhang (f)
7. Longkang Sang (a)
8. Changqian Ma (a, b)
9. Dominic Papineau (c, g)

Affiliations:

a. State Key Laboratory of Geological Processes and Mineral Resources, Wuhan 430074, China

b. Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China

c. Department of Earth and Environmental Sciences, Boston College, Chestnut Hill, MA 02467, USA

d. Nanofabrication Cleanroom Facility, Boston College, Newton, MA 02459, USA

e. Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington DC 20015, USA

f. Mine Planning and Designing Institute of Yilin District, Yichang 443100, China

g. Geophysical Laboratory, Carnegie Institution of Washington, Washington DC 20015, USA

Abstract:

In order to ascertain the origin of granular phosphorites and the roles of microorganisms in phosphogenesis, we conducted comprehensive petrographic surveys and correlated in situ micro-analyses of granular phosphorites from the Doushantuo Formation near Yichang, South China. Phosphatic granules display organically-zoned internal structures often associated with abundant cyanobacteria-like microfossils. The internal ultrastructure of the granules, as documented by Raman microspectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), is characterized by randomly-oriented apatite nano-crystals embedded with ubiquitous carbonaceous particles in the apatite groundmass. These represent primary textures formed by the rapid growth of apatite provided with abundant nucleation sites within microbial biofabrics. NanoSIMS elemental mapping revealed close correspondence of carbon and nitrogen with microfossil structures at the cellular and sub-cellular level. We propose that the Doushantuo granules themselves were formed by microbially-mediated accretionary growth followed by rapid phosphatization occurring at the sediment-water interface. Extracellular polymeric substances (EPS) produced by cyanobacteria would have played crucial roles in these processes by promoting aggregated granule growth in addition to providing nucleation sites for apatite crystallization. While previous studies have suggested a dominant role of sulfur-metabolizing microorganisms in the precipitation of phosphate in phosphorites, new observations indicate that the emplacement of most sulfur-bearing minerals in the Doushantuo phosphorites postdate phosphatization itself. Our new model of phosphorite formation thus places cyanobacterial EPS as an earlier key component of the mineralization of the Doushantuo granular phosphorites.

  

Precambrian Canfield Oceans May Have Inhibited Complex Life

A new model suggests that inhospitable hydrodgen-sulphide rich waters could have delayed the spread of complex life forms in ancient oceans. The research, published online this week in the journal Nature Communications, considers the composition of the oceans 550-700 million years ago and shows that oxygen-poor toxic conditions, which may have delayed the establishment of complex life, were controlled by the biological availability of nitrogen.

In contrast to modern oceans, data from ancient rocks indicates that the deep oceans of the early Earth contained little oxygen, and flipped between an iron-rich state and a toxic hydrogen-sulphide-rich state. The latter toxic sulphidic state is caused by bacteria that survive in low oxygen and low nitrate conditions. The study shows how bacteria using nitrate in their metabolism would have displaced the less energetically efficient bacteria that produce sulphide – meaning that the presence of nitrate in the oceans prevented build-up of the toxic sulphidic state.

The model, developed by researchers at the University of Exeter in collaboration with Plymouth Marine Laboratory, University of Leeds, UCL (University College London) and the University of Southern Denmark, reveals the sensitivity of the early oceans to the global nitrogen cycle. It shows how the availability of nitrate, and feedbacks within the global nitrogen cycle, would have controlled the shifting of the oceans between the two oxygen-free states – potentially restricting the spread of early complex life.

Dr Richard Boyle from the University of Exeter said: "Data from the modern ocean suggests that even in an oxygen-poor ocean, this apparent global-scale interchange between sulphidic and non-sulphidic conditions is difficult to achieve. We've shown here how feedbacks arising from the fact that life uses nitrate as both a nutrient, and in respiration, controlled the interchange between two ocean states. For as long as sulphidic conditions remained frequent, Earth's oceans were inhospitable towards complex life."

Retallack: Ediacaran Fossils Are Terrestrial, Not Marine

Dickensonia: A lichen?

Ancient multicellular fossils long thought to be ancestors of early marine life are remnants of land-dwelling lichen or other microbial colonies, says University of Oregon scientist Gregory Retallack, who has been studying fossil soils of South Australia.

Ediacaran (pronounced EDI-akran) fossils date to 542-635 million years ago. They've been considered fossil jellyfish, worms and sea pens, but are preserved in ways distinct from marine invertebrate fossils. The fossils -- first discovered in 1946 in Australia's Ediacara Hills -- are found in iron-colored impressions similar to plant fossils and microbes in fossil soils.

Retallack, a native of Australia, examined ancient Ediacaran soils with an array of state-of-the-art chemical and microscopic techniques, including an electron microprobe and scanning electron microscope in the UO's CAMCOR Microanalytical Facility headed by John Donovan and rock-analysis technology in the UO's stable isotope laboratory of Ilya Bindeman.

The soils with fossils, Retallack writes in his study, "are distinguished by a surface called 'old elephant skin,' which is best preserved under covering sandstone beds." The healed cracks and lumpy appearance of sandy "old elephant skin" are most like the surface of microbial soil crusts in modern deserts.

"This discovery has implications for the tree of life, because it removes Ediacaran fossils from the ancestry of animals," said Retallack, professor of geological sciences and co-director of paleontological collections at the UO's Museum of Natural and Cultural History. His evidence, mostly gathered from a site in the Flinders Ranges, is presented in a paper placed online ahead of print by the journal Nature.

"These fossils have been a first-class scientific mystery," he said. "They are the oldest large multicellular fossils. They lived immediately before the Cambrian evolutionary explosion that gave rise to familiar modern groups of animals."

Retallack studied numerous Ediacaran fossils and determined that the diversity reflects a preference by the ancient organisms for "unfrozen, low salinity soils, rich in nutrients, like most terrestrial organisms." Thus the fossils in Australia's iconic red-rock ranges, he concludes, were landlubbers. In his closing paragraph, Retallack outlines implications for a variety of other Edicaran fossils, that could have been lichens, other microbial consortia, fungal fruiting bodies, slime molds, flanged pedestals of biological soil crusts, and even casts of needle ice.

Ediacaran fossils, he said, represent "an independent evolutionary radiation of life on land that preceded by at least 20 million years the Cambrian evolutionary explosion of animals in the sea." Increased chemical weathering by large organisms on land may have been needed to fuel the demand of nutrient elements by Cambrian animals. Independent discoveries of Cambrian fossils comparable with Ediacaran ones is evidence, he said, that even in the Cambrian, more than 500 million years ago, life on land may have been larger and more complex than life in the sea.

Retallack leaves open the possibility that some Ediacaran fossils found elsewhere in the world may not be land-based in origin, writing in his conclusion that the many different kinds of these fossils need to be tested and re-evaluated.

I think this one counts as ... out there.  I'd love to see the firestorm this releases!

Paper link.  Nature editorial.

Take With a Grain of Salt: North Koreans Claim Ediacaran Fossils

North Korean researchers have discovered a 620,000,000-year-old fossil of a tubular animal, the first organism with skeletal structure on Earth, the state media reported today.

Researchers from the geology faculty of Kim Il Sung University excavated the fossil of the tubular animal in the Proterozoic era of North Hwanghae province, the Korean Central News Agency (KCNA) said in a report.

According to the report, the tubular animal was the first organism with skeletal structure on Earth. It was an elliptic tube-shape animal with nothing in abdomen.

The researchers said they found fossils of primitive seaweeds and primitive jellyfish belonging to the period of transition from one-cell to multi-cell in 2001.

During their recent in-depth research into the fossil, they discovered the fossil of the 5 cm-long tubular animal again on the same stratum, Xinhua news agency quoted KCNA as saying.

hmmm.

Ediacarans Were Osmotrophs

Research at Virginia Tech has shown that the oldest complex life forms -- living in nutrient-rich oceans more than 540 million years ago – likely fed by osmosis.

The researchers studied two groups of modular Ediacara organisms, the fern-shaped rangeomorphs and the air mattress-shaped erniettomorphs. These macroscopic organisms, typically several inches in size, absorbed nutrients through their outer membrane, much like modern microscopic bacteria, according to the cover story of the Aug. 25, 2009 issue of the Proceedings of the National Academy of Sciences (PNAS), "Osmotrophy in modular Edicara organisms," by Marc Laflamme, Shuhai Xiao, and Michal Kowalewski. Laflamme, now a Postdoctoral Fellow in the Department of Geology and Geophysics at Yale University, did the research as a postdoc in Xiao's lab at Virginia Tech. Xiao and Kowalewski are professors of geobiology in the College of Science at Virginia Tech.

The rangeomorphs had a repeatedly branching system like fern leaves and the erniettomorphs had a folded surface like an inflated air mattress to make tubular modules. "These organisms are unlike any life forms since and so are poorly understood," said Laflamme.

Their feeding strategy has been a topic of controversy, with theories ranging from parasitism to symbiosis to photosynthesis. "Some hypotheses can be ruled out because the organisms lack feeding structures, such as tentacles or mouths, and because many of them lived in the deep ocean where there was no sunlight for photosynthesis" said Xiao.

The researchers decided to simulate various morphological changes in the overall construction of the organisms to test whether it would have been possible for them to attain surface area to volume ratios on the same order as modern bacteria that feed by osmosis. Theoretical models were constructed to explore the effects of length, width, thickness, number of modules, and presence of internal vacuoles, on the surface area of the Precambrian fossils. "Modeling efforts suggest that internal vacuoles – that is, voids filled with fluids or other biologically inert materials – are a particularly effective way of increasing surface-to-volume ratio of complex, macroscopic organisms," said Kowalewski.

They discovered that the two groups (the repeatedly branching rangeomorphs and the air-mattress like erniettomorphs) grew and constructed their bodies in different ways; however both groups attempted to maximize their surface-area to volume ratios in their own way. "The increase in size was clearly accomplished primarily by addition of modules for the erniettomorphs and repetitive branching and inflation of modules for the rangemorphs," Laflamme said. "The repeated branching system in rangeomorphs was essential to allow for a high surface-area to volume ratio necessary for proper osmosis-based feeding."

Today, only microscopic bacteria find it efficient to us only osmosis to feed, although some animals, such as sponges and corals, use osmosis as a supplementary food source. But in the Ediacaran period, 635 to 541 million years ago, with nutrient-rich oceans, "a diffusion-based feeding strategy was more feasible," Laflamme said.

"We believe the Ediacarans were feeding on dissolved organic carbon, which can come in many forms," he said. "It represents the organic material originating from plants, fungi, animals -- you name it, which has dissolved into fats and proteins during natural organic decay. There is a growing body of evidence that in Ediacaran times, due mainly to the absence of animals with true guts capable of packaging organic matter into fecal pellets, there was a much greater pool of dissolved organic nutrients, especially in deeper waters. Without fecal pellets, organic substances would have remained in suspension and decomposed into fats and proteins capable of dissolution into marine waters," he said. "We believe these compounds were then absorbed via osmosis through Ediacaran "skin" due to the high surface-area to volume ratios."

The paper (link):

Osmotrophy in modular Ediacara organisms

1. Marc Laflamme (1)
2. Shuhai Xiao
3. Michał Kowalewski

Department of Geosciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061

1. To whom correspondence should be sent at the present address: Department of Geology and Geophysics, Yale University, P.O. Box 208109, New Haven, CT 06520-8190. E-mail: marc.laflamme@yale.edu

Abstract:

The Ediacara biota include macroscopic, morphologically complex soft-bodied organisms that appear globally in the late Ediacaran Period (575–542 Ma). The physiology, feeding strategies, and functional morphology of the modular Ediacara organisms (rangeomorphs and erniettomorphs) remain debated but are critical for understanding their ecology and phylogeny. Their modular construction triggered numerous hypotheses concerning their likely feeding strategies, ranging from micro-to-macrophagus feeding to photoautotrophy to osmotrophy. Macrophagus feeding in rangeomorphs and erniettomorphs is inconsistent with their lack of oral openings, and photoautotrophy in rangeomorphs is contradicted by their habitats below the photic zone. Here, we combine theoretical models and empirical data to evaluate the feasibility of osmotrophy, which requires high surface area to volume (SA/V) ratios, as a primary feeding strategy of rangeomorphs and erniettomorphs. Although exclusively osmotrophic feeding in modern ecosystems is restricted to microscopic bacteria, this study suggests that (i) fractal branching of rangeomorph modules resulted in SA/V ratios comparable to those observed in modern osmotrophic bacteria, and (ii) rangeomorphs, and particularly erniettomorphs, could have achieved osmotrophic SA/V ratios similar to bacteria, provided their bodies included metabolically inert material. Thus, specific morphological adaptations observed in rangeomorphs and erniettomorphs may have represented strategies for overcoming physiological constraints that typically make osmotrophy prohibitive for macroscopic life forms. These results support the viability of osmotrophic feeding in rangeomorphs and erniettomorphs, help explain their taphonomic peculiarities, and point to the possible importance of earliest macroorganisms for cycling dissolved organic carbon that may have been present in abundance during Ediacaran times.

Ediacaran Animal Fossils Found?

Large spinose microfossils in Ediacaran rocks as resting stages of early animals

1. Phoebe A. Cohena,1,
2. Andrew H. Knollb,1 and
3. Robin B. Kodnerc

-Author Affiliations

1.
Departments of aEarth and Planetary Sciences and
2.
bOrganismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138; and
3.
cFriday Harbor Laboratories, University of Washington, Friday Harbor, WA 98250

1.

Contributed by Andrew H. KnollMarch 2, 2009 (sent for review December 9, 2008)

Abstract

Large (>100 μm), profusely ornamented microfossils comprise a distinctive paleontological component of sedimentary rocks deposited during the Ediacaran Period (635–542 million years ago). Smaller spinose fossils in Paleozoic rocks have commonly been interpreted as algal cysts or phycomata, but the Ediacaran populations differ from modern algal analogs in size, shape, ultrastructure, and internal contents. In contrast, cysts formed during the diapause egg-resting stages of many metazoans share features of size, ornamentation, and internal contents with large ornamented Ediacaran microfossils (LOEMs). Moreover, transmission electron microscopic observations of animal-resting cysts reveal a 3-layer wall ultrastructure comparable to that of LOEM taxa. Interpretation of these distinctive Ediacaran microfossils as resting stages in early metazoan life cycles offers additional perspectives on their functional morphology and stratigraphic distribution. Based on comparisons with modern marine invertebrates, the recalcitrant life stage represented by LOEMs is interpreted as an evolutionary response to prolonged episodes of bottom water anoxia in Ediacaran shelf and platform environments. As predicted by this hypothesis, the later Ediacaran disappearance of LOEM taxa coincides with geochemical evidence for a marked decline in the extent of oxygen-depleted waters impinging on continental shelves and platforms. Thus, the form, diversity, and stratigraphic range of LOEMs illuminate life cycle evolution in early animals as influenced by the evolving redox state of the oceans.

Dude. I'll get the paper once I am at work tomorrow.

Probably Related to What Doug Just Sent Me

Stretching the Envelope of Past Surface Environments: Neoproterozoic Glacial Lakes from Svalbard

Huiming Bao,1* Ian J. Fairchild,2 Peter M. Wynn,3 Christoph Spötl4

The oxygen isotope composition of terrestrial sulfate is affected measurably by many Earth-surface processes. During the Neoproterozoic, severe "snowball" glaciations would have had an extreme impact on the biosphere and the atmosphere. Here, we report that sulfate extracted from carbonate lenses within a Neoproterozoic glacial diamictite suite from Svalbard, with an age of ~635 million years ago, falls well outside the currently known natural range of triple oxygen isotope compositions and indicates that the atmosphere had either an exceptionally high atmospheric carbon dioxide concentration or an utterly unfamiliar oxygen cycle during deposition of the diamictites.

1 Department of Geology and Geophysics, E235 Howe-Russell Complex, Louisiana State University, Baton Rouge, LA 70803, USA.
2 School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK.
3 Department of Geography, University of Lancaster, Lancaster LA1 4YQ, UK.
4 Institut für Geologie und Paläontologie, Leopold-Franzens-Universität Innsbruck, Innrain 52, 6020 Innsbruck, Austria.

Nat Geo has a Popsci version of the above. Now if only I had the paper. Interesting that the Ediacaran had so many interesting and oddball things happening in it. Or is this Cryogenian?

Related link.

Different time frames from what Doug sent me. I didn't get a chance to read what he had. That covers the Great Oxidization Event: here and here. The GOE was 1.8 billion years older. There was a lot more sulfur in the atmosphere then though like both the Ediacaran-Cryogenian Boundary and GOE.

A Precambrian Explosion

Scientists have known for some time that most major groups of complex animals appeared in the fossils record during the Cambrian Explosion, a seemingly rapid evolutionary event that occurred 542 million years ago. Now Virginia Tech paleontologists, using rigorous analytical methods, have identified another explosive evolutionary event that occurred about 33 million years earlier among macroscopic life forms unrelated to the Cambrian animals. They dubbed this earlier event the "Avalon Explosion."

The discovery, reported in the January 4 issue of Science, suggests that more than one explosive evolutionary event may have taken place during the early evolution of animals.

[...]

To test whether other major branches of life also evolved in an abrupt and explosive manner, Virginia Tech graduate students Bing Shen and Lin Dong, along with Xiao and Kowalewski, analyzed the Ediacara fossils: the oldest complex, multicellular organisms that had lived in oceans from 575 to 542 million years ago; that is, before the Cambrian Explosion of animals. "These Ediacara organisms do not have an ancestor-descendant relationship with the Cambrian animals, and most of them went extinct before the Cambrian Explosion," said Shen. “And this group of organisms – most species – seems to be distinct from the Cambrian animals.”

[...]

Surprisingly, however, as shown by Shen and colleagues, these earliest Ediacara life forms already occupied a full morphological range of body plans that would ever be realized through the entire history of Ediacara organisms. "In other words, major types of Ediacara organisms appeared at the dawn of their history, during the Avalon Explosion," Dong said. "Subsequently, Ediacara organisms diversified in White Sea time and then declined in Nama time. But, despite this notable waxing and waning in the number of species, the morphological range of the Avalon organisms were never exceeded through the subsequent history of Ediacara."

[...]

Scientists are still unsure what were the driving forces behind the rapid morphological expansion during the Avalon explosion, and why the morphological range did not expand, shrink, or shift during the subsequent White Sea and Nama stages.

"But, one thing seems certain -- the evolution of earliest macroscopic and complex life also went through an explosive event before to the Cambrian Explosion,” Xiao said. “It now appears that at the dawn of the macroscopic life, between 575 and 520 million years ago, there was not one, but at least two major episodes of abrupt morphological expansion."

Really it ought to be called the Ediacaran, Avalon, or Vendian Explosion. It has little to do with the subsequent evolution of animal life as far as we can tell, but, still, it seems to have been an important stage if for no other reason than it tells an interesting tale in and of itself about life. And its extinction.