Neoproterozoic

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Neoproterozoic
1000 – 538.8 ± 0.2 Ma
Clockwise, from top left: Otavia, a multicellular organism from Tonian period, Snowball Earth glaciations from Cryogenian period, Ediacaran biota from Ediacaran period
Chronology
Proposed redefinition(s)850–541 Ma
Gradstein et al., 2012
Proposed subdivisionsCryogenian Period, 850–630 Ma

Gradstein et al., 2012
Ediacaran Period, 630–541.0 Ma

Gradstein et al., 2012
Etymology
Name formalityFormal
Usage information
Celestial body
Newfoundland, Canada
47°04′34″N 55°49′52″W / 47.0762°N 55.8310°W / 47.0762; -55.8310
Upper GSSP ratified1992[citation needed]

The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago.[2]

It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is preceded by the Mesoproterozoic Era and succeeded by the Paleozoic Era of the Phanerozoic Eon.

The most severe

glaciation known in the geologic record occurred during the Cryogenian, when ice sheets may have reached the equator and formed a "Snowball Earth
".

The earliest fossils of complex

Period. These organisms make up the Ediacaran biota, including the oldest definitive animals
in the fossil record.

According to Rino and co-workers, the sum of the continental crust formed in the Pan-African orogeny and the Grenville orogeny makes the Neoproterozoic the period of Earth's history that has produced most continental crust.[3]

Geology

At the onset of the Neoproterozoic the supercontinent Rodinia, which had assembled during the late Mesoproterozoic, straddled the equator. During the Tonian, rifting commenced which broke Rodinia into a number of individual land masses.

Possibly as a consequence of the low-latitude position of most continents, several large-scale glacial events occurred during the Neoproterozoic Era including the

Marinoan
glaciations of the Cryogenian Period.

These glaciations are believed to have been so severe that there were ice sheets at the equator—a state known as the "Snowball Earth".

Subdivisions

Neoproterozoic time is subdivided into the Tonian (1000–720 Ma), Cryogenian (720–635 Ma) and Ediacaran (635–538.8 Ma) periods.[2]

Russian regional timescale

In the regional timescale of Russia, the Tonian and Cryogenian correspond to the Late Riphean; the Ediacaran corresponds to the Early to middle Vendian.[4] Russian geologists divide the Neoproterozoic of Siberia into the Mayanian (from 1000 to 850 Ma) followed by the Baikalian (from 850 to 650 Ma).[5]

  • Russian timescale for Proterozoic. Neoproterozoic is equivalent to the time span from Late Riphean to Late Vendian.
    Russian timescale for Proterozoic. Neoproterozoic is equivalent to the time span from Late Riphean to Late Vendian.

Paleobiology

The idea of the Neoproterozoic Era was introduced in the 1960s. Nineteenth-century paleontologists set the start of

metazoan fossils older than the classical Precambrian–Cambrian boundary (which is currently dated at 538.8 million years ago).[6][2]

A few of the early animals appear possibly to be ancestors of modern animals. Most fall into ambiguous groups of frond-like organisms; discoids that might be holdfasts for stalked organisms ("medusoids"); mattress-like forms; small calcareous 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 Period 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 unknown animal types.

In addition to Ediacaran biota, two other types of biota were discovered in China. The Doushantuo Formation (of Ediacaran age) preserves fossils of microscopic marine organisms in great detail.[7][contradictory] The Huainan biota (of late Tonian age) consists of small worm-shaped organisms.[8]

keratose sponge fossils have been reported in reefs dated to c. 890 million years before the present, but remain unconfirmed.[9]

Terminal period

The nomenclature for the terminal period of the Neoproterozoic Era has been unstable. Russian and Nordic geologists referred to the last period of the Neoproterozoic as the

Sinian
, and most Australians and North Americans used the name Ediacaran.

However, in 2004, the International Union of Geological Sciences ratified the Ediacaran Period to be a geological age of the Neoproterozoic, ranging from 635 to 538.8 (at the time to 542) million years ago.[10][11] The Ediacaran Period boundaries are the only Precambrian boundaries defined by biologic Global Boundary Stratotype Section and Points, rather than the absolute Global Standard Stratigraphic Ages.

See also

References

External links