Cryogenian
Encyclopedia
The Cryogenian is a geologic period that lasted from . It forms the second geologic
period of the Neoproterozoic
Era, preceded by the Tonian
Period and followed by the Ediacaran
. The Sturtian and Marinoan glaciations, which are the greatest ice ages known to have occurred on Earth and may have covered the entire planet, occurred during this period. These so-called 'snowball earth
' events are the subject of much scientific controversy. The main debate involves whether these glaciations were truly global or merely localised events.
The period has not received the international ratification that all geological time periods undergo (the most recent being the Ediacaran
Period, which was ratified in 2004). The start of the period is defined only on the ages of the rocks and not on any observable and documented global event. This is problematic as estimates of rock ages are variable and are subject to laboratory error. For instance, the Cambrian
Period is marked not by rock younger than a given age ( million years), but by the appearance of the worldwide Treptichnus pedum
diagnostic trace fossil
assemblage. This means that rocks can be recognised as Cambrian when examined in the field and do not require extensive testing to be performed in a lab to find a date. As yet, there is no consensus on what global event is a suitable candidate to mark the start of the Cryogenian Period, and its base is only loosely set to Ma.
suffered the most severe ice ages in its history during this period (Sturtian, Varangian...). Glacier
s extended and contracted in a series of rhythmic pulses, possibly reaching as far as the equator. It is generally considered to be divisible into at least two major worldwide glaciations. The Sturtian glaciation persisted from 750 million years ago to 700 Ma, and the Marinoan glaciation
which ended approximately 635 Ma. The deposits of glacial tillite also occur in places that were at low latitudes during the Cryogenian, a phenomenon which led to the hypothesis of deeply-frozen planetary oceans called "Snowball Earth
".
broke up, and the supercontinent Pannotia
began to form.
Geology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
period of the Neoproterozoic
Neoproterozoic
The Neoproterozoic Era is the unit of geologic time from 1,000 to 542.0 ± 1.0 million years ago. The terminal Era of the formal Proterozoic Eon , it is further subdivided into the Tonian, Cryogenian, and Ediacaran Periods...
Era, preceded by the Tonian
Tonian
The Tonian is the first geologic period in the Neoproterozoic Era and lasted from 1000 Mya to 850 Mya...
Period and followed by the Ediacaran
Ediacaran
The Ediacaran Period , named after the Ediacara Hills of South Australia, is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon...
. The Sturtian and Marinoan glaciations, which are the greatest ice ages known to have occurred on Earth and may have covered the entire planet, occurred during this period. These so-called 'snowball earth
Snowball Earth
The Snowball Earth hypothesis posits that the Earth's surface became entirely or nearly entirely frozen at least once, some time earlier than 650 Ma . Proponents of the hypothesis argue that it best explains sedimentary deposits generally regarded as of glacial origin at tropical...
' events are the subject of much scientific controversy. The main debate involves whether these glaciations were truly global or merely localised events.
The period has not received the international ratification that all geological time periods undergo (the most recent being the Ediacaran
Ediacaran
The Ediacaran Period , named after the Ediacara Hills of South Australia, is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon...
Period, which was ratified in 2004). The start of the period is defined only on the ages of the rocks and not on any observable and documented global event. This is problematic as estimates of rock ages are variable and are subject to laboratory error. For instance, the Cambrian
Cambrian
The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...
Period is marked not by rock younger than a given age ( million years), but by the appearance of the worldwide Treptichnus pedum
Treptichnus pedum
Treptichnus pedum is regarded as the earliest widespread complex trace fossil...
diagnostic trace fossil
Trace fossil
Trace fossils, also called ichnofossils , are geological records of biological activity. Trace fossils may be impressions made on the substrate by an organism: for example, burrows, borings , urolites , footprints and feeding marks, and root cavities...
assemblage. This means that rocks can be recognised as Cambrian when examined in the field and do not require extensive testing to be performed in a lab to find a date. As yet, there is no consensus on what global event is a suitable candidate to mark the start of the Cryogenian Period, and its base is only loosely set to Ma.
Climate
The name of the geologic period refers to the very cold global climate of the Cryogenian: characteristic glacial deposits indicate that EarthEarth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
suffered the most severe ice ages in its history during this period (Sturtian, Varangian...). Glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
s extended and contracted in a series of rhythmic pulses, possibly reaching as far as the equator. It is generally considered to be divisible into at least two major worldwide glaciations. The Sturtian glaciation persisted from 750 million years ago to 700 Ma, and the Marinoan glaciation
Marinoan glaciation
The Marinoan glaciation was a period of worldwide glaciation that lasted from approximately 650 to 635 Ma during the Cryogenian period. The glaciation may have covered the entire planet, in an event called the Snowball Earth...
which ended approximately 635 Ma. The deposits of glacial tillite also occur in places that were at low latitudes during the Cryogenian, a phenomenon which led to the hypothesis of deeply-frozen planetary oceans called "Snowball Earth
Snowball Earth
The Snowball Earth hypothesis posits that the Earth's surface became entirely or nearly entirely frozen at least once, some time earlier than 650 Ma . Proponents of the hypothesis argue that it best explains sedimentary deposits generally regarded as of glacial origin at tropical...
".
Paleogeography
During the Cryogenian, the supercontinent RodiniaRodinia
In geology, Rodinia is the name of a supercontinent, a continent which contained most or all of Earth's landmass. According to plate tectonic reconstructions, Rodinia existed between 1.1 billion and 750 million years ago, in the Neoproterozoic era...
broke up, and the supercontinent Pannotia
Pannotia
Pannotia, first described by Ian W. D. Dalziel in 1997, is a hypothetical supercontinent that existed from the Pan-African orogeny about six hundred million years ago to the end of the Precambrian about five hundred and fifty million years ago. It is also known as the Vendian supercontinent...
began to form.