End-Ediacaran extinction

Evidence suggesting that a mass extinction occurred at the end of the Ediacaran period, 542 million years ago, includes:

  • A mass extinction of acritarchs
  • The sudden disappearance of the Ediacara biota and calcifying organisms;
  • The time gap before Cambrian organisms "replaced" them.
  • the unconfirmed Massive Pre-Cambrian Impact Structure (MAPCIS), a 2000 km impact crater in central Australia, has been tentatively dated to this time period

Pre-Ediacaran organisms

During the Ediacaran period, two main groups of organisms are found in the fossil record: the "Ediacara biota" of soft-bodied organisms, preserved by microbial mats; and calcifying organisms such as Cloudina and Namacalathus, which had a carbonate skeleton.[1] Because both these groups disappear abruptly at the end of the Ediacaran period, 542 ± 0.3 million years ago, their disappearance cannot simply represent the closure of a preservational window,[2] as had previously been suspected.[1]

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.[3]

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.[4] 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),[5] just not one that is related to the Ediacara biota.[6]

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. One such organism is the agglutinated foramanifera Platysolenites.[7] Swartpuntia is one well known late Ediacaran vendobiont, which survived into the earliest Cambrian.[8] Cambrian Erytholus is a similar sandstone cast to Ediacaran Ventogyrus.[9] Ordovician and Silurian Rutgersella[10] and Devonian Protonympha[11] have been interpreted as surviving vendobionts, comparable with Ediacaran Dickinsonia and Spriggina, respectively.

Geochemical evidence

A negative δ13C excursion—a geochemical signal often associated with mass extinctions—is observed at the end of the Ediacaran period.[12]

Sedimentary evidence

This period is reflected in the geological record by an increase in black shale deposition,[13] representing global anoxia.[14] 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.[3][13][15]

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References
  1. 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.
  2. 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.
  3. Wille, M; Nägler, T.F.; Lehmann, B; Schröder, S; Kramers, J.D (June 2008). "Hydrogen sulphide release to surface waters at the Precambrian/Cambrian boundary". Nature. 453 (7196): 767–9. Bibcode:2008Natur.453..767W. doi:10.1038/nature07072. PMID 18509331.
  4. 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.
  5. See Ediacaria
  6. 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, 286, London: Geological Society, pp. 277–295, doi:10.1144/SP286.20, ISBN 9781862392335, OCLC 156823511CS1 maint: uses authors parameter (link)
  7. 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.
  8. Jensen, Sören, James G. Gehling, and Mary L. Droser (1998). "Ediacara-type fossils in Cambrian sediments". Nature. 393 (6685): 567–569. Bibcode:1998Natur.393..567J. doi:10.1038/31215.CS1 maint: multiple names: authors list (link)
  9. Retallack, G.J. (2011). "Problematic megafossils in Cambrian palaeosols of South Australia". Palaeontology. 54 (6): 1223–1242. doi:10.1111/j.1475-4983.2011.01099.x.
  10. Retallack, G.J. (2015). "Reassessment of the Silurian problematicum Rutgersella as another post-Ediacaran vendobiont". Alcheringa. 39 (4): 573–588. doi:10.1080/03115518.2015.1069483.
  11. Retallack, G.J. (2018). "Reassessment of the Devonian Problematicum Protonympha as another post-Ediacaran vendobiont". Lethaia. 50. doi:10.1111/let12253 (inactive 2020-06-06).
  12. Zhu; Babcock, L; Peng, S (2006). "Advances in Cambrian stratigraphy and paleontology: Integrating correlation techniques, paleobiology, taphonomy and paleoenvironmental reconstruction". Palaeoworld. 15 (3–4): 217. doi:10.1016/j.palwor.2006.10.016.
  13. Schroder, S.; Grotzinger, J.P. (2007). "Evidence for anoxia at the Ediacaran-Cambrian boundary: the record of redox-sensitive trace elements and rare earth elements in Oman". Journal of the Geological Society. 164 (1): 175–187. Bibcode:2007JGSoc.164..175S. doi:10.1144/0016-76492005-022. S2CID 18376742.
  14. 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.
  15. "What caused the mass extinction of Earth's first animals? Unravelling mystery of the Ediacaran-Cambrian transition". ScienceDaily. Retrieved 20 February 2020.
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