The Neoproterozoic Era is the unit of geologic time from 1,000 to 542 +/- 0.3 million years ago.^[1] The terminal Era of the formal Proterozoic Eon (or the informal "Precambrian"), it is further subdivided into the Tonian, Cryogenian, and Ediacaran Periods. The most severe glaciation known in the geologic record occurred during the Cryogenian, when ice sheets reached the equator and formed a possible "Snowball Earth"; and the earliest fossils of multicellular life are found in the Ediacaran, including the earliest animals. // For other uses, see time scale. ... Mega-annum, usually abbreviated as Ma, is a unit of time equal to one million years. ... The Proterozoic (IPA: ) is a geological eon representing a period before the first abundant complex life on Earth. ... The Precambrian (or Pre-Cambrian) is an informal name for the eons of the geologic timescale that came before the current Phanerozoic eon. ... The Tonian (from Greek tonas, stretch) is the first geologic period in the Neoproterozoic Era and lasted from 1000 Ma to 850 Ma (million years ago). ... The Cryogenian Period (from Greek cryos ice and genesis birth) is the second geologic period of the Neoproterozoic Era, followed by the Ediacaran Period. ... The Ediacaran Period (from the Ediacara Hills of South Australia) is the last geological period of the Neoproterozoic Era, just before the Cambrian. ... A glaciation (a created composite term meaning Glacial Period, referring to the Period or Era of, as well as the process of High Glacial Activity), often called an ice age, is a geological phenomenon in which massive ice sheets form in the Arctic and Antarctic and advance toward the equator. ... World map showing the equator in red In tourist areas, the equator is often marked on the sides of roads The equator marked as it crosses Ilhéu das Rolas, in São Tomé and Príncipe. ... The Snowball Earth hypothesis is a controversial hypothesis (Sankaran, 2003) that attempts to explain a number of phenomena noted in the geological record by proposing that an ice age that took place in the Neoproterozoic was so severe that the Earths oceans froze over completely, with only heat from... Phyla Radiata Cnidaria Ctenophora - Comb jellies Bilateria Protostomia Acoelomorpha Platyhelminthes - Flatworms Nemertina - Ribbon worms Gastrotricha Gnathostomulida - Jawed worms Micrognathozoa Rotifera - Rotifers Acanthocephala Priapulida Kinorhyncha Loricifera Entoprocta Nematoda - Roundworms Nematomorpha - Horsehair worms Cycliophora Mollusca - Mollusks Sipuncula - Peanut worms Annelida - Segmented worms Tardigrada - Water bears Onychophora - Velvet worms Arthropoda - Insects, etc. ... Animalia redirects here. ...

Paleogeology

Geologically, the Neoproterozoic is thought to comprise a time of complex continental motion as a supercontinent called Rodinia broke up into perhaps as many as eight pieces. Possibly as a consequence of continental rifting, several massive worldwide glaciations occurred during the Era including the Sturtian and Marinoan glaciations, the most severe the Earth has ever known. These are believed to have been so severe as to bring icecaps to the equator, leading to a state known as the "Snowball Earth". Depiction of Rodinia at time of initial breakup. ... The Cryogenian Period (from Greek cryos ice and genesis birth) is the second geologic period of the Neoproterozoic Era, followed by the Ediacaran Period. ... The Cryogenian Period (from Greek cryos ice and genesis birth) is the second geologic period of the Neoproterozoic Era, followed by the Ediacaran Period. ... The Snowball Earth hypothesis is a controversial hypothesis (Sankaran, 2003) that attempts to explain a number of phenomena noted in the geological record by proposing that an ice age that took place in the Neoproterozoic was so severe that the Earths oceans froze over completely, with only heat from...

Paleobiology

Main article: Ediacaran biota

The idea of the Neoproterozoic Era came on the scene relatively recently — after about 1960. Nineteenth century paleontologists set the start of multicelled life at the first appearance of hard-shelled animals called trilobites and archeocyathids. This set the beginning of the Cambrian period. In the early 20th century, paleontologists started finding fossils of multicellular animals that predated the Cambrian boundary. A complex fauna was found in South West Africa in the 1920s but was misdated. Another was found in South Australia in the 1940s but was not thoroughly examined until the late 1950s. Other possible early fossils were found in Russia, England, Canada, and elsewhere (see Ediacaran biota). Some were determined to be pseudofossils, but others were revealed to be members of rather complex biotas that are still poorly understood. At least 25 regions worldwide yielded metazoan fossils prior to the classical Cambrian boundary.^[2] This page may meet Wikipedia’s criteria for speedy deletion. ... Phyla Subkingdom Parazoa Porifera (sponges) Subkingdom Agnotozoa Placozoa Orthonectida Rhombozoa Subkingdom Metazoa Radiata Cnidaria Ctenophora - Comb jellies Bilateria Protostomia Acoelomorpha Platyhelminthes - Flatworms Nemertina - Ribbon worms Gastrotricha Gnathostomulida - Jawed worms Micrognathozoa Rotifera - Rotifers Acanthocephala Priapulida Kinorhyncha Loricifera Entoprocta Nematoda - Roundworms Nematomorpha - Horsehair worms Cycliophora Mollusca - Mollusks Sipuncula - Peanut worms Annelida - Segmented... Orders Agnostida Redlichiida Corynexochida Lichida Phacopida Suborder: Librostoma Proetida Asaphida Harpetida Ptychopariida For the robot vacuum cleaner, see Electrolux Trilobite. ... The Archeocyatha, also called Archaeocyathids, were sessile, reef-building marine organisms that lived during the Lower Cambrian period (500-600 million years ago). ... The Cambrian is a major division of the geologic timescale that begins about 542 ± 1. ... A world map showing the continent of Africa Africa is the worlds second-largest and second most-populous continent, after Asia. ... This page may meet Wikipedia’s criteria for speedy deletion. ... Phyla Subkingdom Parazoa Porifera (sponges) Subkingdom Agnotozoa Placozoa Orthonectida Rhombozoa Subkingdom Metazoa Radiata Cnidaria Ctenophora - Comb jellies Bilateria Protostomia Acoelomorpha Platyhelminthes - Flatworms Nemertina - Ribbon worms Gastrotricha Gnathostomulida - Jawed worms Micrognathozoa Rotifera - Rotifers Acanthocephala Priapulida Kinorhyncha Loricifera Entoprocta Nematoda - Roundworms Nematomorpha - Horsehair worms Cycliophora Mollusca - Mollusks Sipuncula - Peanut worms Annelida - Segmented...

A few of the early animals appear possibly to be ancestors of modern animals. Most fall into ambiguous groups of frond-like animals(?); discoids that might be holdfasts for stalked animals(?) ("medusoids"); mattress-like forms; small calcaerous tubes; and armored animals of unknown provenance. These were most commonly known as Vendian biota until the formal naming of the Period, and are currently known as Ediacaran biota. Most were soft bodied. The relationships, if any, to modern forms are obscure. Some paleontologists relate many or most of these forms to modern animals. Others acknowledge a few possible or even likely relationships but feel that most of the Ediacaran forms are representatives of (an) unknown animal type(s).

Terminal period

Main article: Ediacaran

The nomenclature for the terminal period of the Neoproterozoic has been unstable. Russian geologists referred to the last period of the Neoproterozoic as the Vendian, and the Chinese called it the Sinian, and most Australians and North Americans used the name Ediacaran. However, in 2004, the International Union of Geological Sciences ratified the Ediacaran age to be a geological age of the Neoproterozoic, ranging from 630 +5/-30 to 542 +/- 0.3 million years ago.^[1] The Ediacaran boundaries are the only Precambrian boundaries defined by biologic Global Boundary Stratotype Section and Points, rather than the absolute Global Standard Stratigraphic Ages. The Ediacaran Period (from the Ediacara Hills of South Australia) is the last geological period of the Neoproterozoic Era, just before the Cambrian. ... The Vendian biota (also known as Vendian forms, Vendian fauna(s), and Vendazoa) are a group of ancient lifeforms that are found in rocks a bit older than the Cambrian faunas that represent the oldest fossils of classical paleontology. ... The Ediacaran Period (from the Ediacara Hills of South Australia) is the last geological period of the Neoproterozoic Era, just before the Cambrian. ... 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... The Ediacaran Period (from the Ediacara Hills of South Australia) is the last geological period of the Neoproterozoic Era, just before the Cambrian. ... A Global Boundary Stratotype Section and Point, abbreviated GSSP, is an internationally agreed upon stratigraphic section which serves as the reference section for a particular boundary on the geologic timescale. ... A Global Standard Stratigraphic Age, often abbreviated GSSA, is an internationally agreed upon chronological age used to define the boundaries between different periods or epochs on the geologic timescale. ...

Notes

References

• Gradstein, F. M.; Ogg, J. G.; Smith, A. G. (eds.) (2005). A Geologic Time Scale 2004. Cambridge University Press. ISBN 0-521-78673-8. 
• Knoll, A. H.; Walter, M.; Narbonne, G.; Christie-Blick, N. (2006). "The Ediacaran Period: a new addition to the geologic time scale". Lethaia 39: 13-30. DOI:10.1080/00241160500409223.  PDF here.