Impressions of the Ediacaran fossils Dickinsonia (at center) with the smaller anchor shaped Parvancorina (left) in sandstone of the Ediacara Member from the Nilpena Ediacara National Park in South Australia.
Photo: Scott Evans.
A big problem for Creationists, especially those who believe the Bible was written by an infallible creator god, so think Earth is just a few thousand years old, is that science keeps finding evidence that Earth is billions of years old, and finding fossils of the life-forms that were around then.
As though that wasn't refutation enough, a team of scientists from Virginia Tech have now explained the mass extinction that wiped out most of these early life forms several billion years ago - giving the lie that they were intelligently designed by a god with the ability of foresight. Such a god would have known about the future mass extinctions and either prevented it, designed his creations to survive it or at least waited till it was safe to create things. Creating things to go extinct is not the act of an intelligent or sane creator.
This mass extinction appears not to have been a sudden event, such as that that resulted in the extinction of the non-avian dinosaurs and large marine reptile predators, but to have occurred in two phases that resulted in a loss of about 80% of species and separated by about 10 million years.
But before creationists get over-excited, this does not mean all the Ediacarans were extinct at the Cambrian 'explosion' so the Cambrian biota had no ancestors. It means that there were still about 20% of the Ediacaran biota to evolve over the 6 million years of the Cambrian 'explosion' into the Cambrian biota.
The Ediacaran mass extinction was probably caused by falling Oxygen levels as Ediacarans that had evolved large mass to surface-area ratios suffered from a loss of oxygen more so than those which had retained a smaller mass to surface area ratio.
How this mass extinction was identified and related to changes in global oxygen levels was the subject of an open access paper in PNAS and a Virginal Tech News item:
A new study by Virginia Tech geobiologists traces the cause of the first known mass extinction of animals to decreased global oxygen availability, leading to the loss of a majority of animals present near the end of the Ediacaran Period some 550 million years ago.Technical details is in the team's open access paper on PNAS:
The research spearheaded by Scott Evans, a postdoctoral researcher in the Department of Geosciences, part of the Virginia Tech College of Science, shows this earliest mass extinction of about 80 percent of animals across this interval.Evans’ work was published today [7 November 2022] in the Proceedings of the National Academy of Sciences, a peer-reviewed journal of the National Academy of Sciences. The study was co-authored by Shuhai Xiao, also a professor in the Department of Geosciences, and several researchers led by Mary Droser from the University of California Riverside’s Department of Earth and Planetary Sciences, where Evans earned his master’s degree and Ph.D.This included the loss of many different types of animals, however those whose body plans and behaviors indicate that they relied on significant amounts of oxygen seem to have been hit particularly hard. This suggests that the extinction event was environmentally controlled, as are all other mass extinctions in the geologic record.
Dr Scott D. Evans, lead author
Department of Geosciences
Virginia Tech, Blacksburg, VA, USA
Environmental changes, such as global warming and deoxygenation events, can lead to massive extinction of animals and profound disruption and reorganization of the ecosystem. This has been demonstrated repeatedly in the study of Earth history, including this work on the first extinction documented in the fossil record. This study thus informs us about the long-term impact of current environmental changes on the biosphere.
Shuhai Xiao, co-author
Department of Geosciences
Virginia Tech, Blacksburg, VA, USA.The study by Evans and Xiao is timelier than one would think. In an unconnected study, Virginia Tech scientists recently found that anoxia, the loss of oxygen availability, is affecting the world’s fresh waters. The cause? The warming of waters brought on by climate change and excess pollutant runoff from land use. Warming waters diminish fresh water’s capacity to hold oxygen, while the breakdown of nutrients in runoff by freshwater microbes gobbles up oxygen.[What exactly caused the drop in global oxygen?] The short answer to how this happened is we don't really know. It could be any number and combination of volcanic eruptions, tectonic plate motion, an asteroid impact, etc., but what we see is that the animals that go extinct seem to be responding to decreased global oxygen availability.
Dr Scott D. EvansSome perspective: The Ediacaran Period spanned roughly 96 million years, bookended on either side by the end of Cryogenian Period — 635 million years ago — and the beginning of the Cambrian Period — 539 million years ago. The extinction event comes just before a significant break in the geologic record, from the Proterozoic Eon to the Phanerozoic Eon.Our study shows that, as with all other mass extinctions in Earth's past, this new, first mass extinction of animals was caused by major climate change — another in a long list of cautionary tales demonstrating the dangers of our current climate crisis for animal life/
Dr Scott D. Evans
There are five known mass extinctions that stand out in the history of animals, the “Big Five,” according to Xiao, including the Ordovician-Silurian Extinction (440 million years ago), the late Devonian Extinction (370 million years ago), the Permian-Triassic Extinction (250 million years ago), the Triassic-Jurassic Extinction (200 million years ago), and the Cretaceous-Paleogene Extinction (65 million years ago).
Impressions of the Ediacaran fossils Dickinsonia (at left) and related but rare form Andiva (at right) in sandstone of the Ediacara Member from the Nilpena Ediacara National Park in South Australia.Photo courtesy of Scott Evans.
“Mass extinctions are well recognized as significant steps in the evolutionary trajectory of life on this planet,” Evans and team wrote in the study. Whatever the instigating cause of the mass extinction, the result was multiple major shifts in environmental conditions. “Particularly, we find support for decreased global oxygen availability as the mechanism responsible for this extinction. This suggests that abiotic controls have had significant impacts on diversity patterns throughout the more than 570 million-year history of animals on this planet,” the authors wrote.
Fossil imprints in rock tell researchers how the creatures that perished in this extinction event would have looked. And they looked, in Evans’ words, “weird.”The study, like scores of other recent publications, came out of the COVID-19 pandemic. Because Evans, Xiao, and their team couldn't get access to the field, they decided to put together a global database based mostly on published records to test ideas about changing diversity. “Others had suggested that there might be an extinction at this time, but there was a lot of speculation. So we decided to put together everything we could to try and test those ideas.” Evans said. Much of the data used in the study was collected by Droser and several graduate students from the University of California Riverside.These organisms occur so early in the evolutionary history of animals that in many cases they appear to be experimenting with different ways to build large, sometimes mobile, multicellular bodies. There are lots of ways to recreate how they look, but the take-home is that before this extinction the fossils we find don't often fit nicely into the ways we classify animals today. Essentially, this extinction may have helped pave the way for the evolution of animals as we know them.
Dr Scott D. Evans
Impressions of the Ediacaran fossil Dickinsonia, one of the first mobile animals, in sandstone of the Ediacara Member from the Nilpena Ediacara National Park in South Australia.">Photo courtesy of Scott Evans.
SignificanceMass extinctions alone are enough to refute the childish notion of creation by an omniscient designer, let alone an intelligent one, and of course one reason the Ediacaran biota doesn't get a mention in the Bible is because, like all the other extinct taxons, the primitive Bronze Age authors had not got the slightest idea that they ever existed or that Earth was old enough to have gone through several major geological era lasting hundreds of millions of years, and several mass extinctions which had wiped out most of the earlier species or they wouldn't have assumed everything was magically created as it was then, But then they only had what little knowledge their culture possessed out of which to concoct a believable story.
Mass extinctions are well recognized as significant steps in the evolutionary trajectory of life on this planet. Here, we document the oldest known extinction of animals and test for potential causes. Our results indicate that, like younger diversity crises, this event was caused by major shifts in environmental conditions. Particularly, we find support for decreased global oxygen availability as the mechanism responsible for this extinction. This suggests that abiotic controls have had significant impacts on diversity patterns throughout the more than 570-My history of animals on this planet.
Abstract
The Ediacara Biota—the oldest communities of complex, macroscopic fossils—consists of three temporally distinct assemblages: the Avalon (ca. 575–560 Ma), White Sea (ca. 560–550 Ma), and Nama (ca. 550–539 Ma). Generic diversity varies among assemblages, with a notable decline at the transition from White Sea to Nama. Preservation and sampling biases, biotic replacement, and environmental perturbation have been proposed as potential mechanisms for this drop in diversity. Here, we compile a global database of the Ediacara Biota, specifically targeting taphonomic and paleoecological characters, to test these hypotheses. Major ecological shifts in feeding mode, life habit, and tiering level accompany an increase in generic richness between the Avalon and White Sea assemblages. We find that ∼80% of White Sea taxa are absent from the Nama interval, comparable to loss during Phanerozoic mass extinctions. The paleolatitudes, depositional environments, and preservational modes that characterize the White Sea assemblage are well represented in the Nama, indicating that this decline is not the result of sampling bias. Counter to expectations of the biotic replacement model, there are minimal ecological differences between these two assemblages. However, taxa that disappear exhibit a variety of morphological and behavioral characters consistent with an environmentally driven extinction event. The preferential survival of taxa with high surface area relative to volume may suggest that this was related to reduced global oceanic oxygen availability. Thus, our data support a link between Ediacaran biotic turnover and environmental change, similar to other major mass extinctions in the geologic record.
Soft-bodied fossils of the Ediacara Biota comprise the oldest communities of macroscopic organisms, including animals, and are critical for understanding the advent and diversification of complex life (1, 2). However, equally important are the dynamics that lead to the disappearance of such animals (3–6). Two major drops in diversity of the Ediacara Biota have been recognized, an initial decrease between the White Sea and Nama assemblages and a second across the Ediacaran–Cambrian boundary (Fig. 1 and ref. (5)). Although these events may be related, they are separated by more than 10 My and vary in magnitude and taxa impacted. The exceptional conditions required to preserve the Ediacara Biota also leave uncertainty around potential taphonomic biases that may contribute to such patterns. Diversity crises shaped the course of evolution in the Phanerozoic. Thus, a comprehensive understanding of each of these Ediacaran events is critical to determine the fate of Earth’s early animals.Similar mechanisms have been proposed for losses of diversity during both the White Sea–Nama and Ediacaran–Cambrian transitions. One suggestion is that taxa did not go extinct but instead are not preserved in subsequent intervals (the “Cheshire cat” model of ref. (3)). Biases may include differences in the paleolatitudes and paleoenvironments sampled as well as variable taphonomic windows preserving fossils from each assemblage (7). Alternatively, these events may represent true extinctions triggered by either biotic or abiotic factors or some combination thereof (3, 5). The biotic replacement model, generally attributing the demise of the Ediacara Biota to competition with more advanced “Cambrian-style” metazoans, focuses on the impact of bioturbators as indicated by increases in trace fossil diversity (e.g., ref. (8)). Such ecosystem engineers are proposed to have fundamentally changed carbon packaging and fluid transport in the latest Ediacaran (3, 4, 8–10). Alternatively, the catastrophic extinction model posits that a major environmental perturbation led to the rapid loss of a variety of Ediacara taxa (3, 5) supported by geochemical data for environmental conditions, such as changes in oxygen availability (e.g., ref. (11)).Raw generic diversity (black squares), bootstrapped diversity (gray triangles), bootstrapped (42) per taxon extinction rate (solid blue), and origination rate (dashed green). Error bars represent 1 SD. For bootstrapping analysis, database occurrences were randomly subsampled to 50 occurrences.M
Here, we use a holistic approach, combining the distribution, taphonomy, and ecology of constituent taxa, to investigate changes in the Ediacara Biota through compilation of global occurrence data. Specifically, we test for potential sampling biases in the form of major differences in the paleolatitudes, facies associations, or preservational modes that could account for apparent changes in taxonomic composition. Based on the lack of correlation between these factors, we then investigate paleoecological trends through the Ediacaran under the assumption that, as with other diversity crises in the fossil record (12), patterns of selectivity across these intervals should reflect the factors responsible for such change. Analysis was conducted by comparing differences between the three assemblages—necessarily representing time-averaged groups of organisms on the order of millions to tens of millions of years—as in previous studies (e.g., refs. (3, 5, 13)). However, we also examined patterns of change involving taxa that survived and went extinct at the end of the White Sea assemblage to investigate changes on relatively shorter geologic timescales.
Fig. 2. Paleogeographic distribution of fossil localities (A) within the three assemblages of the Ediacara Biota based on continental configurations by Merdith et al. (14) and pie charts with the distribution of paleoenvironments (B) and modes of preservation (C) sampled for each assemblage, with “n” referring to the No. of formations/facies sampled in each time bin. See SI Appendix, Fig. S1 for locality labels.
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