End-Ediacaran extinction

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The end-Ediacaran extinction is a mass extinction believed to have occurred near the end of the Ediacaran period, the final period of the Proterozoic eon. Evidence suggesting that such a mass extinction occurred includes a massive reduction in diversity of acritarchs, the sudden disappearance of the Ediacara biota and calcifying organisms, and the time gap before Cambrian organisms "replaced" them. Some lines of evidence suggests that there may have been two distinct pulses of the extinction event, one occurring 550  million years ago and the other 539  million years ago. [1]

Contents

Evidence

Biotic evidence

Ediacaran organisms

Most of the Ediacaran organisms featured in this image went extinct because of the extinction event. Note: this is an outdated reconstruction, and the "jellyfish" in the image likely did not exist Life in the Ediacaran sea.jpg
Most of the Ediacaran organisms featured in this image went extinct because of the extinction event. Note: this is an outdated reconstruction, and the "jellyfish" in the image likely did not exist

During the Ediacaran period, two main groups of organisms are found in the fossil record: the "Ediacaran biota" of soft-bodied organisms, preserved by microbial mats; and calcifying organisms such as Cloudina and Namacalathus , which had a carbonate skeleton. [2] Because both these groups disappear abruptly at the end of the Ediacaran period, 538.8  ± 0.2 million years ago, [3] their disappearance cannot simply represent the closure of a preservational window, [4] as had previously been suspected. [2]

Additionally, the late Ediacaran saw a faunal turnover between the White Sea biota, which lived between 560 and 550 million years ago, and the Nama biota, which lived between 550 and 539 million years ago. [5] The transition from the White Sea to the Nama biota saw a major reduction in diversity that was not recovered during the interval of the depauperate Nama biota, which has been attributed to either increased biological competition [1] or an anoxic event [5] and in either case suggests that large-scale extinction began well before the boundary between the Ediacaran and Cambrian.[ citation needed ]

Post-Ediacaran survivors

The fossil record of the earliest Cambrian, just after the Ediacaran period, shows a sudden increase in burrowing activity and diversity. However, the Cambrian explosion of animals that gave rise to body fossils did not happen instantaneously. This implies that the "explosion" did not represent animals "replacing" the incumbent organisms, and pushing them gradually to extinction; rather, the data are more consistent with a radiation of animals to fill in vacant niches, left empty as an extinction cleared out the pre-existing fauna. [6]

The theory that all Ediacarans became extinct at the start of the Cambrian is disproven if any post-Ediacaran survivors are found. Organisms from the lower Cambrian, such as Thaumaptilon , were once thought to be Ediacarans, but this hypothesis no longer has many adherents. [7] One possible Ediacaran survivor whose status is still open to scrutiny is Ediacaria booleyi , a purported holdfast structure known from the upper Cambrian. If this does turn out to be a true Ediacaran, the biota cannot have disappeared completely. Disbelievers have claimed that the fossils don't actually have a biological origin, which doesn't seem to be the case—evidence is mounting to suggest that it is an organism (or at least of biological origin, perhaps a microbial colony), [8] just not one that is related to the Ediacara biota. [9]

Some organisms clearly survived the extinction since life on Earth has continued. However, very few organisms are known from both sides of the Ediacaran-Cambrian boundary.[ citation needed ] One such organism is the agglutinated foraminifera Platysolenites . [10] Swartpuntia is one well known late Ediacaran vendobiont, which survived into the earliest Cambrian. [11] Cambrian Erytholus is a similar sandstone cast to Ediacaran Ventogyrus . [12] Ordovician and Silurian Rutgersella [13] and Devonian Protonympha [14] have been interpreted as surviving vendobionts, comparable with Ediacaran Dickinsonia and Spriggina , respectively.

Geochemical evidence

Negative δ13C excursions—geochemical signals often associated with mass extinctions—are observed during the Late Ediacaran. The Shuram excursion occurred around the same time as the boundary between the White Sea and Nama assemblages. [15] Another major negative carbon isotope excursion is known to have occurred at the end of the Ediacaran period and the beginning of the Cambrian. [16]

Sedimentary evidence

The transition between the White Sea and Nama biotas near the end of the Ediacaran is reflected in the geological record by an increase in black shale deposition, [17] representing global anoxia. [18] This may be related to global changes in oceanic circulation and may have been the worst marine anoxic event of the last 550 million years, [6] [17] [19] although its causal relationship with the White Sea-Nama biotic turnover is controversial and has been challenged by studies concluding that this expansion of anoxia postdated the turnover. [20]

Related Research Articles

<span class="mw-page-title-main">Cambrian</span> First period of the Paleozoic Era, 539–485 million years ago

The Cambrian is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran period 538.8 Ma to the beginning of the Ordovician Period 485.4 Ma.

<span class="mw-page-title-main">Ediacaran</span> Third and last period of the Neoproterozoic Era

The Ediacaran is a geological period of the Neoproterozoic Era that spans 96 million years from the end of the Cryogenian Period at 635 Mya to the beginning of the Cambrian Period at 538.8 Mya. It is the last period of the Proterozoic Eon as well as the last of the so-called "Precambrian supereon", before the beginning of the subsequent Cambrian Period marks the start of the Phanerozoic Eon, where recognizable fossil evidence of life becomes common.

The cloudinids, an early metazoan family containing the genera Acuticocloudina, Cloudina and Conotubus, lived in the late Ediacaran period about 550 million years ago. and became extinct at the base of the Cambrian. They formed millimetre-scale conical fossils consisting of calcareous cones nested within one another; the appearance of the organism itself remains unknown. The name Cloudina honors the 20th-century geologist and paleontologist Preston Cloud.

<i>Dickinsonia</i> Extinct genus of early animals

Dickinsonia is a genus of extinct organism, most likely an animal, that lived during the late Ediacaran period in what is now Australia, China, Russia, and Ukraine. It is one of the best known members of the Ediacaran biota. The individual Dickinsonia typically resembles a bilaterally symmetrical ribbed oval. Its affinities are presently unknown; its mode of growth has been considered consistent with a stem-group bilaterian affinity, though various other affinities have been proposed. It lived during the late Ediacaran. The discovery of cholesterol molecules in fossils of Dickinsonia lends support to the idea that Dickinsonia was an animal, though these results have been questioned.

<i>Charnia</i> Genus of frond-like lifeforms

Charnia is an extinct genus of frond-like lifeforms belonging to the Ediacaran biota with segmented, leaf-like ridges branching alternately to the right and left from a zig-zag medial suture. The genus Charnia was named after Charnwood Forest in Leicestershire, England, where the first fossilised specimen was found. Charnia is significant because it was the first Precambrian fossil to be recognized as such.

<span class="mw-page-title-main">Vendobionta</span> Group of extinct creatures that were part of the Ediacaran biota

Vendobionts or Vendozoans (Vendobionta) are a proposed very high-level, extinct clade of benthic organisms that made up of the majority of the organisms that were part of the Ediacaran biota. It is a hypothetical group and at the same time, it would be the oldest of the animals that populated the Earth about 580 million years ago, in the Ediacaran period. They became extinct shortly after the so-called Cambrian explosion, with the introduction of fauna forming groups more recognizably related to modern animals. It is very likely that the whole Ediacaran biota is not a monophyletic clade and not every genus placed in its subtaxa is an animal.

<i>Rangea</i> Fossil taxon

Rangea is a frond-like Ediacaran fossil with six-fold radial symmetry. It is the type genus of the rangeomorphs.

Namacalathus is a problematic metazoan fossil occurring in the latest Ediacaran. The first, and only described species, N. hermanastes, was first described in 2000 from the Nama Group of central and southern Namibia.

<span class="mw-page-title-main">Ediacaran biota</span> Life of the Ediacaran period

The Ediacaranbiota is a taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period. These were enigmatic tubular and frond-shaped, mostly sessile, organisms. Trace fossils of these organisms have been found worldwide, and represent 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 small shelly fauna, small shelly fossils (SSF), or early skeletal fossils (ESF) are mineralized fossils, many only a few millimetres long, with a nearly continuous record from the latest stages of the Ediacaran to the end of the Early Cambrian Period. They are very diverse, and there is no formal definition of "small shelly fauna" or "small shelly fossils". Almost all are from earlier rocks than more familiar fossils such as trilobites. Since most SSFs were preserved by being covered quickly with phosphate and this method of preservation is mainly limited to the late Ediacaran and early Cambrian periods, the animals that made them may actually have arisen earlier and persisted after this time span.

The Cambrian explosion is an interval of time approximately 538.8 million years ago in the Cambrian period of the early Paleozoic when a sudden radiation of complex life occurred, and practically all major animal phyla started appearing in the fossil record. It lasted for about 13 to 25 million years and resulted in the divergence of most modern metazoan phyla. The event was accompanied by major diversification in other groups of organisms as well.

<i>Eoandromeda</i> Species of Ediacaran animal

Eoandromeda is an Ediacaran organism consisting of eight radial spiral arms, and known from two taphonomic modes: the standard Ediacara type preservation in Australia, and as carbonaceous compressions from the Doushantuo formation of China, where it is abundant.

Ediacaran type preservation relates to the dominant preservational mode in the Ediacaran period, where Ediacaran organisms were preserved as casts on the surface of microbial mats.

<span class="mw-page-title-main">Stratigraphy of the Cambrian</span>

The Stratigraphy of the Cambrian period currently has several schemes used for ordering geologic formations from the period. The International Commission on Stratigraphy−ICS scheme has set a stratotype section for the base of the Cambrian, dated quite accurately to 538.8 ± 0.2 million years ago. Russian and Chinese scientists have developed a different scheme.

<span class="mw-page-title-main">John P. Grotzinger</span>

John P. Grotzinger is the Fletcher Jones Professor of Geology at California Institute of Technology and chair of the Division of Geological and Planetary Sciences. His works primarily focus on chemical and physical interactions between life and the environment. In addition to biogeological studies done on Earth, Grotzinger is also active in research into the geology of Mars and has made contributions to NASA's Mars Exploration Program.

<i>Stromatoveris</i> Extinct genus of invertebrates

Stromatoveris psygmoglena is a genus of basal petalonam from the Chengjiang deposits of Yunnan that was originally aligned with the fossil Charnia from the Ediacara biota. However, such an affinity was thought to be developmentally implausible and so S. psygmoglena was thought to be either a sessile basal ctenophore, or a sessile organism closely related to ctenophores instead. Nevertheless, a 2018 phylogenetic analysis by Jennifer Hoyal Cuthill and Jian Han indicated that Stromatoveris was a member of Animalia and closely related to ediacaran frond-like lifeforms.

<span class="mw-page-title-main">Nama Group</span>

The Nama Group is a 125,000 square kilometres (48,000 sq mi) megaregional Vendian to Cambrian group of stratigraphic sequences deposited in the Nama foreland basin in central and southern Namibia. The Nama Basin is a peripheral foreland basin, and the Nama Group was deposited in two early basins, the Zaris and Witputs, to the north, while the South African Vanrhynsdorp Group was deposited in the southern third. The Nama Group is made of fluvial and shallow-water marine sediments, both siliciclastic and carbonate. La Tinta Group in Argentina is considered equivalent to Nama Group.

<i>Hallidaya</i> Extinct species of simple animal

The Ediacaran fossil Hallidaya, a close relative of Skinnera lived in Belomorian of the Late Ediacaran period prior to the Cambrian explosion and thrived in the marine strata on the ocean floor of what is now considered Australia. These fossils were disk-shaped organisms that were slightly dome shaped with tri-radial symmetry. These Ediacaran organisms thrived by living in low-energy inner shelf, in the wave- and current-agitated shoreface, and in the high-energy distributary systems.

<span class="mw-page-title-main">Nama assemblage</span> Ediacaran biotic assemblage

The Nama assemblage was the last of the Ediacaran biotic assemblages. Following the Avalon and White Sea assemblages, it spanned from c. 550 Ma to c. 539 Ma, coinciding with the Terminal Ediacaran biozone. The assemblage was characterized by a faunal turnover, with the decline of the preexisting White Sea biota. The drop of diversity has been compared to the mass extinctions of the Phanerozoic. A second drop of diversity occurred at the Ediacaran–Cambrian boundary, concluding the Nama assemblages with the end-Ediacaran extinction.

References

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  2. 1 2 Amthor, Joachim E.; Grotzinger, John P.; Schröder, Stefan; Bowring, Samuel A.; Ramezani, Jahandar; Martin, Mark W.; Matter, Albert (2003). "Extinction of Cloudina and Namacalathus at the Precambrian-Cambrian Boundary in Oman". Geology. 31 (5): 431–434. Bibcode:2003Geo....31..431A. doi:10.1130/0091-7613(2003)031<0431:EOCANA>2.0.CO;2. ISSN   0091-7613.
  3. ↑ "Stratigraphic Chart 2022" (PDF). International Stratigraphic Commission. February 2022. Retrieved 25 April 2022.
  4. ↑ Marshall, Charles R. (2006). "Explaining The Cambrian "Explosion" Of Animals". Annual Review of Earth and Planetary Sciences. 34: 355–384. Bibcode:2006AREPS..34..355M. doi:10.1146/annurev.earth.33.031504.103001. S2CID   85623607.
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  7. ↑ Antcliffe, Jonathan B.; Brasier, Martin D. (2007). "Charnia and sea pens are poles apart". Journal of the Geological Society. 164 (1): 49–51. Bibcode:2007JGSoc.164...49A. doi:10.1144/0016-76492006-080. S2CID   130602154.
  8. ↑ See Ediacaria
  9. ↑ MacGabhann, B. A.; Murray, J.; Nicholas, C. (2007), "Ediacaria booleyi: weeded from the Garden of Ediacara?", in Vickers-Rich, Patricia; Komarower, Patricia (eds.), The Rise and Fall of the Ediacaran Biota, Special publications, vol. 286, London: Geological Society, pp. 277=295, doi:10.1144/SP286.20, ISBN   978-1-86239-233-5, OCLC   156823511
  10. ↑ Kontorovich, A; Varlamov, A; Grazhdankin, D; Karlova, G; Klets, A; Kontorovich, V; Saraev, S; Terleev, A; Belyaev, S; et al. (2008). "A section of Vendian in the east of West Siberian Plate (based on data from the Borehole Vostok 3)". Russian Geology and Geophysics. 49 (12): 932. Bibcode:2008RuGG...49..932K. doi:10.1016/j.rgg.2008.06.012.
  11. ↑ Jensen, Sören; James G. Gehling; Mary L. Droser (1998). "Ediacara-type fossils in Cambrian sediments". Nature. 393 (6685): 567–569. Bibcode:1998Natur.393..567J. doi:10.1038/31215. S2CID   205001064.
  12. ↑ Retallack, G.J. (2011). "Problematic megafossils in Cambrian palaeosols of South Australia". Palaeontology. 54 (6): 1223–1242. Bibcode:2011Palgy..54.1223R. doi: 10.1111/j.1475-4983.2011.01099.x . S2CID   130692406.
  13. ↑ Retallack, G.J. (2015). "Reassessment of the Silurian problematicum Rutgersella as another post-Ediacaran vendobiont". Alcheringa. 39 (4): 573–588. Bibcode:2015Alch...39..573R. doi:10.1080/03115518.2015.1069483. S2CID   54780312.
  14. ↑ Retallack, G.J. (2018). "Reassessment of the Devonian Problematicum Protonympha as another post-Ediacaran vendobiont". Lethaia. 50. doi:10.1111/let12253 (inactive 2024-09-13).{{cite journal}}: CS1 maint: DOI inactive as of September 2024 (link)
  15. ↑ Erwan Le Guerroué; et al. (Apr 2006). "Chemostratigraphic and sedimentological framework of the largest negative carbon isotopic excursion in Earth history: The Neoproterozoic Shuram Formation (Nafun Group, Oman)". Precambrian Research. 146 (1–2): 68–92. Bibcode:2006PreR..146...68L. doi:10.1016/j.precamres.2006.01.007.
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  18. ↑ Fike, D.A.; Grotzinger, J.P.; Pratt, L.M.; Summons, R.E. (2006). "Multi-Stage Ediacaran Ocean Oxidation and Its Impact on Evolutionary Radiation". Geochimica et Cosmochimica Acta. 70 (18S): 173. Bibcode:2006GeCAS..70Q.173F. doi:10.1016/j.gca.2006.06.347.
  19. ↑ "What caused the mass extinction of Earth's first animals? Unravelling mystery of the Ediacaran-Cambrian transition". ScienceDaily. Retrieved 20 February 2020.
  20. ↑ Tostevin, Rosalie; Clarkson, Matthew O.; Gangl, Sophie; Shields, Graham A.; Wood, Rachel A.; Bowyer, Fred; Penny, Amelia M.; Stirling, Claudine H. (15 January 2019). "Uranium isotope evidence for an expansion of anoxia in terminal Ediacaran oceans". Earth and Planetary Science Letters . 506: 104–112. Bibcode:2019E&PSL.506..104T. doi:10.1016/j.epsl.2018.10.045. hdl: 20.500.11820/25fe1837-1045-4698-bdb8-4516c7b26a38 . S2CID   134663328 . Retrieved 17 December 2022.
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