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The Neoproterozoic Era is the unit of
geologic time Geology (from the Ancient Greek Ancient Greek includes the forms of the used in and the from around 1500 BC to 300 BC. It is often roughly divided into the following periods: (), Dark Ages (), the period (), and the period (). ...

geologic time
from 1 billion to 541 million years ago. It is the last era of the
Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic The Phanerozoic Eon is the current geologic eon in the geologic time scale The geologi ...

Precambrian
Supereon and the
Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 541million years ago. It is the most recent part of the Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest par ...
Eon; it is subdivided into the
Tonian The Tonian (from grc, τόνος, tónos, meaning "stretch") is the first geologic period The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geolo ...
,
Cryogenian The Cryogenian (, from grc, κρύος, krýos, meaning "cold" and , romanized: , meaning "birth") is a geologic period that lasted from . It forms the second geologic period of the Neoproterozoic era (geology), Era, preceded by the Tonian Perio ...
, and
Ediacaran The Ediacaran Period ( ) is a geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of ...
Periods. It is preceded by the
Mesoproterozoic The Mesoproterozoic Era is a geology, geologic era (geology), era that occurred from . The Mesoproterozoic was the first period of Earth's history of which a fairly definitive geological record survives. Continents existed during the preceding era ...
Era and succeeded by the
Paleozoic The Paleozoic (or Palaeozoic) Era ( ; from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Eu ...
Era of the
Phanerozoic The Phanerozoic Eon is the current in the , and the one during which abundant and has existed. It covers million years to the present, and it began with the Period when animals first developed hard shells preserved in the fossil record. The ...
Eon. The most severe
glaciation A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age An ice age is a long period of reduction in the temperature of Earth Earth is the third planet from the Sun and the o ...
known in the geologic record occurred during the Cryogenian, when
ice sheet In glaciology Lateral moraine on a glacier joining the Gorner Glacier, Zermatt">Gorner_Glacier.html" ;"title="moraine on a glacier joining the Gorner Glacier">moraine on a glacier joining the Gorner Glacier, Zermatt, Swiss Alps. The moraine is ...

ice sheet
s may have reached the
equator The Equator is a circle of latitude, about in circumference, that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the N ...

equator
and formed a "
Snowball Earth The Snowball Earth hypothesis proposes that, during one or more of Earth's Greenhouse and icehouse Earth, icehouse climates, the Earth's surface, planet's surface became entirely or nearly entirely frozen. It is believed that this occurred someti ...
". The earliest fossils of complex multicellular life are found in the
Ediacaran The Ediacaran Period ( ) is a geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of ...
Period. These organisms make up the
Ediacaran biota The Ediacaran (; formerly Vendian) biota is a Taxonomy (biology), taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period (c. 635–541 Year#mya, Mya). These were composed of enig ...
, including the oldest definitive
animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells ...

animal
s in the fossil record. According to Rino and co-workers, the sum of the
continental crust Continental crust is the layer of igneous Igneous rock (derived from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the ...
formed in the
Pan-African orogeny The Pan-African orogeny was a series of major Neoproterozoic The Neoproterozoic Era is the unit of geologic time from 1,000 million to 541 million years ago. It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivid ...
and the
Grenville orogeny The Grenville orogeny was a long-lived Mesoproterozoic mountain-building event associated with the assembly of the supercontinent Rodinia. Its record is a prominent Orogeny, orogenic belt which spans a significant portion of the North American co ...
makes the Neoproterozoic the period of Earth's history that has produced most continental crust.


Geology

At the onset of the Neoproterozoic the supercontinent
Rodinia Rodinia (from the Russian родить, ''rodit'', meaning "to beget, to give birth", or родина, ''rodina'', meaning "motherland, birthplace") was a Neoproterozoic supercontinent that assembled 1.1–0.9 billion years ago and broke up 750 ...

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
Sturtian The Sturtian glaciation was a glaciation, or perhaps multiple glaciations, during the Cryogenian Period when the Earth experienced repeated large-scale glaciations. The duration of the Sturtian glaciation has been variously defined,with dates rangin ...
and
Marinoan The Marinoan glaciation was a period of worldwide glaciation A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier A glacier ( ...
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 The Snowball Earth hypothesis proposes that, during one or more of Earth's Greenhouse and icehouse Earth, icehouse climates, the Earth's surface, planet's surface became entirely or nearly entirely frozen. It is believed that this occurred someti ...
".


Subdivisions

Neoproterozoic time is subdivided into the
Tonian The Tonian (from grc, τόνος, tónos, meaning "stretch") is the first geologic period The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geolo ...
(1000–720 Ma),
Cryogenian The Cryogenian (, from grc, κρύος, krýos, meaning "cold" and , romanized: , meaning "birth") is a geologic period that lasted from . It forms the second geologic period of the Neoproterozoic era (geology), Era, preceded by the Tonian Perio ...
(720–635 Ma) and
Ediacaran The Ediacaran Period ( ) is a geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of ...
(635–541 Ma) periods.


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. Russian geologists divide the Neoproterozoic of
Siberia Siberia (; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part of R ...

Siberia
into the Mayanian (from 1000 to 850 Ma) followed by the Baikalian (from 850 to 650 Ma).


Paleobiology

The idea of the Neoproterozoic Era was introduced in the 1960s. Nineteenth-century paleontologists set the start of
multicellular A multicellular organism is an organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular ...
life at the first appearance of hard-shelled arthropods called
trilobite Trilobites (; meaning "three lobes") are a group of marine s that form the Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the of the ( ...

trilobite
s and
archeocyathid sponges
archeocyathid sponges
at the beginning of the
Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These peri ...
Period. In the early 20th century, paleontologists started finding fossils of multicellular animals that predated the Cambrian. A complex fauna was found in South West
Africa Africa is the world's second-largest and second-most populous continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', ...

Africa
in the 1920s but was inaccurately dated. Another fauna was found in South Australia in the 1940s, but it was not thoroughly examined until the late 1950s. Other possible early animal fossils were found in Russia, England, Canada, and elsewhere (see
Ediacaran biota The Ediacaran (; formerly Vendian) biota is a Taxonomy (biology), taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period (c. 635–541 Year#mya, Mya). These were composed of enig ...
). Some were determined to be
pseudofossil Pseudofossils are inorganic In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavi ...
s, but others were revealed to be members of rather complex biotas that remain poorly understood. At least 25 regions worldwide have yielded
metazoan Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, ...
fossils older than the classical Precambrian–Cambrian boundary (which is currently dated at ). 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 and Hainan Formation).
Molecular phylogeny Molecular phylogenetics () is the branch of phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram A diagram is a symb ...
suggests that animals may have emerged even earlier in the Proterozoic, but physical evidence for such animal life is lacking. Possible keratose sponge fossils have been reported in reefs dating back to 890 million years before the present, but remain unconfirmed.


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 Vendian, while Chinese geologists referred to it 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 to million years ago. The Ediacaran Period boundaries are the only Precambrian boundaries defined by biologic
Global Boundary Stratotype Section and Point A Global Boundary Stratotype Section and Point (GSSP) is an internationally agreed upon reference point on a stratigraphic through Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic syste ...
s, rather than the absolute
Global Standard Stratigraphic Age In the stratigraphy sub-discipline of geology, a Global Standard Stratigraphic Age, abbreviated GSSA, is a chronological reference point and criterion in the geologic record used to define the boundaries (an internationally sanctioned wikt:benchmar ...
s.


See also

*


References


External links


Neoproterozoic (chronostratigraphy scale)
{{Authority control Geological eras