Evolutionary Biology

Edenic Period

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Definition

caption Trilobite fossil dating to the early Edenic Period. Source: C.Michael Hogan fossil collection

The Edenic Period is a span of time in which prehistoric speciation and extinction rates were deemed to be in average long term equilibrium, before the ascent and influence of man on other species existence. Scientists have established this epoch to encompass a group of geologic time intervals commencing approximately 545 million years before present, or about the time hard shelled animals appeared on Earth. The Edenic Period spans the Paleozoic and Mesozoic periods of geologic time as well as the Paleogene, Miocene, Pliocene epochs and the preponderance of the Pleistocene; the Edenic Period is generally an overlap with the Phanerozoic, except that the Edenic Period is defined to have ended in the late Pleistocene prior to the Holocene.

The end of the Edenic Period is generally imputed to be somewhere between 50,000 to 10,000 years before present. Even though  the species of Homo sapiens was somewhat well evolved prior to that time, the human population earlier  than 50,000 years ago is deemed to have been sufficiently small that man had relatively little marginal impact on biodiversity. Thus scientists have employed this term since the nineteenth century, even before they could accurately reckon basic benchmark dates important in geology and paleontology corresponding to the evolution of macroscopic flora. (Gray. 1890)

Edenic Period extinction rate

The extinction rate during the Edenic Period is usually referred to as the background extinction rate, or that rate which occurred before substantial influence of humans. It is important to understand that this Edenic Period extinction rate is specifically defined to be a long term time average, such that mass extinction events within the Edenic Period are simply "averaged through" for the purposes of computing a prehistoric background extinction rate that is meaningful over very long term geologic time.  The Edenic Period extinction rate has been estimated by fossil records, pollen core samples, geological formations and other research data in the fields of paleontology and geology. The resulting best estimate for the Edenic Period extinction rate is one species lost per one million years.(Wilson. 2005)

Fossil records reveal that the typical span for a species existence during the Edenic Period is roughly five million years; however, it is worth noting that some species have survived much longer than others, disproving an evolutionary axiom previously posited by some, that evolution implies a continual improved adaption in all niches that could eventually doom every taxon. For example, Devonian sturgeons and blue-green algae illustrate organisms that survived for a much greater species life than most taxa. (Rossatto et al. 2006)  Furthermore, during the Edenic period there were five identifiable mass extinctions, periods in which the extinction rate skyrocketed. These events occurred in the Late Ordovician, Late Devonian, Permian, Triassic and an occurrence called the K/T event. (Jeffries. 1997) In contrast the current ongoing human induced mass extinction is known as the Holocene Mass Extinction; this modern event appears much more sharply peaked and potentially capable of the highest percentage of total species lost than any of the prior mass extinctions. 

 

caption Number of genera plotted over the Edenic Period. Source: Wikipedia commons

 

 Speciation versus extinction

During the Edenic Period the fossil and pollen core records reveal that the rate of species formation approximately balanced the rate of species extinctions, both estimated at about one species per one million years; moreover, there is thought to.have been a slight positive bias toward species formation so that the number of species on Earth reached a maximum immediately prior to the ascent of man or the onset of the Holocene Mass Extinction. 

Taxonomic distinctions

Scientists often characterize the background rate of extinction by family or lineage to the extent the fossil record permits. The unit of measurement, E/MSY, is the number of species driven extinct per annum per one million species imputed to the lineage during the Edenic Period.(Hassan. 2005)  Mammalian background extinctions are then estimated to lie between 0.21 and 0.46 E/MSY. (Regan et al. 2001) It has been suggested that further analysis of extinction rates during the Edenic Period may provide clues as to which extant taxa have the greatest vulnerability fo extinction, since the fossil record shows clear patterns in survival of certain genera and families. (Lawton and May. 1995) It has been cautioned that extrapolation of taxonomic vulnerability is likely to underestimate future extinction rates, since many of the most vulnerable extant species have highly restricted geographic ranges; furthermore, many of these taxa may have already entered a population bottleneck or reached a population near the minimum viable population size. (Chivian and Bernstein. 2008)

Conclusion

Chiefly from analysis of the fossil record, there is considerable insight on the rate of speciation and extinction over an extended time frame, dating from roughly 545 million years before present until a time approximately 50,000 years before present; this interval is known as the Edenic Period, a span in which most of macroscopic life on Earth evolved and was significantly not influenced by the presence of humans. Furthermore, scientists have been able to deduce a background extinction rate for this period, which is a useful point of comparison for use by conservation biologists. The present rate of extinctions induced by humans appears to be running at approximately 10,000 times the background rate and is likely to be accelerating.

References

*  Peter Gray. 1890. The Succession of Plant Life upon the Earth. Transactions and journal of proceedings, Dumfriesshire and Galloway Natural History and Antiquarian Society, Dumfriesshire, Scotland.

*  E.O. Wilson. 2005. The Future of Life. Alfred A. Knopf. New York, New York, USA

*  Cesar Augusto Rossatto, Ricky Lee Allen and Marc Pruyn. 2006. Reinventing critical pedagogy. 258 pages. Rowman and Littlefield Publishers. Lanham, Maryland, USA

*  Mike J. Jeffries. 1997. Biodiversity and conservation. 208 pages. Routledge

*  Rashid M. Hassan, Robert Scholes and Neville Ash. 2005.Ecosystems and human well-being: current state and trends. 917 pages

*  H.M. Regan, R. Lupia,  A.N. Drinnan and M.A. Burgman. 2001. The currency and tempo of extinction. the American Naturalist, 157(1)*  John H. Lawton and Robert McCredie May. 1995. Extinction rates. 233 pages

*  Eric Chivian and Aaron Bernstein. 2008. Sustaining life: how human health depends on biodiversity. Secretariat of the Convention on Biological Diversity, United Nations Development Programme, 542 pages

 

Glossary

Citation

Hogan, C. (2014). Edenic Period. Retrieved from http://www.eoearth.org/view/article/51cbeda67896bb431f693011

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