Marinoan glaciation
Encyclopedia
The Marinoan glaciation was a period of worldwide glaciation that lasted from approximately 650 to 635 Ma (million years ago) during the Cryogenian
period. The glaciation may have covered the entire planet, in an event called the Snowball Earth
. The end of the glaciation may have been sped by the release of methane
from equatorial permafrost
.
era. There were three (or possibly four) significant ice ages during the late Neoproterozoic. These periods of nearly complete glaciation of Earth are often referred to as "Snowball Earth", where it is hypothesized that at times the planet was covered by ice 1–2 km (0.621372736649807–1.2 mi) thick. Of these glaciations, the Marinoan was the most significant, whereas the Sturtian glaciation was a shorter, but still worldwide glaciation. The Kaigas glaciation is considered the earliest of Cryogenian glaciations. Other Cryogenian glaciations were probably small and not global as compared to the Marinoan or Sturtian glaciations.
During the Marinoan glaciation, characteristic glacial deposits indicate that Earth
suffered the most severe ice ages in its history. Glacier
s extended and contracted in a series of rhythmic pulses, possibly reaching as far as the equator.
archipelago and South Australia. In Guizhou Province, China, glacial rocks were found to be underlying and overlaying a layer of volcanic ash
es which contained zircon
minerals, which could be dated through radioisotopes. Glacial deposits in south Australia are approximately the same age (about 630 Ma), confirmed by similar stable carbon isotopes, mineral deposits (including sedimentary barite
), and other unusual sedimentary structures. Two diamictite
-rich layers in the top 1 km (0.621372736649807 mi) of the 7 km (4.3 mi) Neoproterozoic strata of the northeastern Svalbard archipelago represent the first and final phases of the Marinoan glaciation.
Cryogenian
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...
period. The glaciation may have covered the entire planet, in an event called the 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...
. The end of the glaciation may have been sped by the release of methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
from equatorial permafrost
Permafrost
In geology, permafrost, cryotic soil or permafrost soil is soil at or below the freezing point of water for two or more years. Ice is not always present, as may be in the case of nonporous bedrock, but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of...
.
Cryogenian Snowball Earth
Emerging evidence suggests that the Earth underwent a number of glaciations during the NeoproterozoicNeoproterozoic
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. There were three (or possibly four) significant ice ages during the late Neoproterozoic. These periods of nearly complete glaciation of Earth are often referred to as "Snowball Earth", where it is hypothesized that at times the planet was covered by ice 1–2 km (0.621372736649807–1.2 mi) thick. Of these glaciations, the Marinoan was the most significant, whereas the Sturtian glaciation was a shorter, but still worldwide glaciation. The Kaigas glaciation is considered the earliest of Cryogenian glaciations. Other Cryogenian glaciations were probably small and not global as compared to the Marinoan or Sturtian glaciations.
During the Marinoan glaciation, characteristic glacial deposits indicate that Earth
Earth
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. 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.
Evidence
Even though much evidence has been lost through geological changes, field investigations show evidence of the Marinoan glaciation in China, SvalbardSvalbard
Svalbard is an archipelago in the Arctic, constituting the northernmost part of Norway. It is located north of mainland Europe, midway between mainland Norway and the North Pole. The group of islands range from 74° to 81° north latitude , and from 10° to 35° east longitude. Spitsbergen is the...
archipelago and South Australia. In Guizhou Province, China, glacial rocks were found to be underlying and overlaying a layer of volcanic ash
Volcanic ash
Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...
es which contained zircon
Zircon
Zircon is a mineral belonging to the group of nesosilicates. Its chemical name is zirconium silicate and its corresponding chemical formula is ZrSiO4. A common empirical formula showing some of the range of substitution in zircon is 1–x4x–y...
minerals, which could be dated through radioisotopes. Glacial deposits in south Australia are approximately the same age (about 630 Ma), confirmed by similar stable carbon isotopes, mineral deposits (including sedimentary barite
Barite
Baryte, or barite, is a mineral consisting of barium sulfate. The baryte group consists of baryte, celestine, anglesite and anhydrite. Baryte itself is generally white or colorless, and is the main source of barium...
), and other unusual sedimentary structures. Two diamictite
Diamictite
Diamictite : through and µεικτός : mixed) is a poorly or non-sorted conglomerate or breccia with a wide range of clasts, up to 25% of them gravel sized...
-rich layers in the top 1 km (0.621372736649807 mi) of the 7 km (4.3 mi) Neoproterozoic strata of the northeastern Svalbard archipelago represent the first and final phases of the Marinoan glaciation.