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Encyclopedia > Snowball Earth
One computer simulation of conditions during the Snowball Earth period.
One computer simulation of conditions during the Snowball Earth period.[1]

The Snowball Earth hypothesis as it currently stands[2] proposes that the Earth was entirely covered by ice in part of the Cryogenian period of the Proterozoic eon, and perhaps at other times in the history of Earth. It was developed to explain sedimentary glacial deposits at tropical latitudes during the Cryogenian period (850 to 630 million years ago) and other enigmatic features of the Cryogenian geological record. After the last big freeze ended, multicellular evolution began to accelerate. Snowball Earth remains controversial, and is contested by various scientists who dispute the geophysical feasibility of a completely frozen ocean, or the geological evidence on which the hypothesis is based. Image File history File links Size of this preview: 436 × 600 pixelsFull resolution (600 × 825 pixel, file size: 110 KB, MIME type: image/jpeg)a, Ice extent at equilibrium (Mollweide projection) for a snowball Earth simulation. ... Image File history File links Size of this preview: 436 × 600 pixelsFull resolution (600 × 825 pixel, file size: 110 KB, MIME type: image/jpeg)a, Ice extent at equilibrium (Mollweide projection) for a snowball Earth simulation. ... Look up Hypothesis in Wiktionary, the free dictionary. ... This article is about Earth as a planet. ... Snowflakes by Wilson Bentley, 1902 Ice is the name given to any one of the 14 known solid phases of water. ... 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 Proterozoic (IPA: ) is a geological eon representing a period before the first abundant complex life on Earth. ... Look up eon, Eon, EON in Wiktionary, the free dictionary. ... The Earth, photographed from Apollo 17 in 1972. ... Two types of sedimentary rock: limey shale overlaid by limestone. ... Austrias longest glacier, the Pasterze, winds its 8 km (5 mile) route at the foot of Austrias highest mountain, the Grossglockner A glacier is a large, long-lasting river of ice that is formed on land and moves in response to gravity. ... A noontime scene from the Philippines on a day when the sun is almost directly overhead. ... Latitude,usually denoted symbolically by the Greek letter phi, , gives the location of a place on Earth north or south of the equator. ... The Cryogenian Period (from Greek cryos ice and genesis birth) is the second geologic period of the Neoproterozoic Era, followed by the Ediacaran Period. ... This article is about evolution in biology. ...


The beginning of a Snowball Earth event could be facilitated by an equatorial continental distribution, which allows rapid, unchecked weathering of continental rocks, absorbing vast quantities of carbon dioxide from the atmosphere. The depletion of this greenhouse gas causes ice accumulation, which further cools the planet by reflecting solar energy back to space. The runaway system would lead a new ice-covered equilibrium with equatorial temperatures similar to modern-day Antarctica. In order to meet Wikipedias quality standards, this article requires cleanup. ...


To break out of the frozen condition, huge quantities of greenhouse gases such as carbon dioxide and methane, emitted primarily by volcanic activity, would have to accumulate over millions of years. Once melting began, however, it would be quick, perhaps only 1000 years. Methane is a chemical compound with the molecular formula CH4. ...


Weathering of glacial sediments, by reacting with carbon dioxide, and fertilising oceanic photosynthesisers, may have eventually drawn down enough of the greenhouse gas to instigate another Snowball Earth. This article needs additional references or sources for verification. ...


Sedimentary features usually formed by glaciers, found in what may have been equatorial locations at the time of deposition, have been taken as evidence implying global ice cover. Many other features of the sedimentary record are easily explained by extensive glacial cover. Geochemical evidence from rocks associated with low-latitude glacial deposits have been interpreted to show a crash in oceanic life during the glacial times, which is consistent with a freezing of the surface oceans. Two types of sedimentary rock: limey shale overlaid by limestone. ... Glacial and Glaciation redirect here. ... 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. ... Deposition is a word used in many fields to describe different processes: In law, deposition is the taking of testimony outside of court. ...


Whilst the presence of glaciers is not disputed, the idea that the entire planet was covered in ice is more contentious, leading some scientists to prefer a "slushball" to a "snowball". In a slushball scenario a band of ice-free, or ice-thin, waters remains around the equator, allowing for a continued hydrologic cycle. This appeals to scientists who believe that certain features of the sedimentary record can only be explained by rapidly moving ice, which would require somewhere ice free to move to, or that observed sedimentary structures could only form below open water. Attempts to construct computer models of a Snowball Earth have also struggled to accommodate global ice cover, without fundamental changes in the laws and constants which govern the planet. Attempts have been made to explain equatorial ice-deposits by claiming Earth's spin axis or magnetic field changed dramatically. Recent research using observed geochemical cyclicity in clastic rocks suggests that the "Snowball" periods were punctuated by warm spells, similar to ice age cycle in recent Earth history. 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 water cycle—technically known as the hydrologic cycle—is the circulation of water within the earths hydrosphere, involving changes in the physical state of water between liquid, solid, and gas phases. ... Clastic rocks refers to rocks formed from fragments of pre-existing rock. ... Variations in CO2, temperature and dust from the Vostok ice core over the last 400 000 years For the animated movie, see Ice Age (movie). ...


Snowball Earth has profound implications on the history of life on Earth. While many refugia have been postulated, global ice cover would certainly have ravaged ecosystems dependent on sunlight. The melting of the ice may have presented many new opportunities for diversification, and may indeed have driven the rapid evolution which took place directly at the end of the Cryogenian period. For other uses, see Life (disambiguation). ... Proposed Amazonian Refugia from Haffer, 1969 In the most basic biological sense refugia (singular: refugium) refer to locations of isolated or relict populations of once widespread animal or plant species. ... A coral reef near the Hawaiian islands is an example of a complex marine ecosystem. ...

Snowball Period
(millions of years ago)

Contents

What happened

Initiating "Snowball Earth"

A tropical distribution of the continents is, perhaps counter-intuitively, necessary to allow the initiation of a Snowball Earth. Firstly, tropical continents are more reflective than open ocean, and so absorb less of the sun's heat: most absorption of solar energy on Earth today occurs in tropical oceans.[3]


Further, tropical continents are subject to more rainfall, which leads to increased river discharge - and erosion. When exposed to air, silicate rocks undergo weathering reactions which remove carbon dioxide from the atmosphere. These reactions proceed in the general form: Rock-forming mineral + CO2 + H2O → cations + bicarbonate + SiO2. An example of such a reaction is the weathering of wollastonite: In chemistry, a silicate is a compound containing an anion in which one or more central silicon atoms are surrounded by electronegative ligands. ... Wollastonite is a calcium inosilicate mineral (CaSiO3) that may contain small amounts of iron, magnesium, and manganese substituting for calcium. ...

CaSiO3 + 2CO2 + H2O → Ca2+ + SiO2 + 2HCO3-

The released calcium cations react with the dissolved bicarbonate in the ocean to form calcium carbonate as a chemically precipitated sedimentary rock. This transfers carbon dioxide, a greenhouse gas, from the air into the geosphere, and, in steady-state on geologic time scales, offsets the carbon dioxide emitted from volcanoes into the atmosphere. General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Standard atomic weight 40. ... For baking soda, see Sodium bicarbonate In inorganic chemistry, a bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. ... Calcium carbonate is a chemical compound, with chemical formula CaCO3. ... Two types of sedimentary rock: limey shale overlaid by limestone. ... In order to meet Wikipedias quality standards, this article requires cleanup. ... In the most general sense, the geosphere is the region of space that is dominated by geogenic matter (originating from and bound to the Earth). ... For other uses, see Volcano (disambiguation). ...


A paucity of suitable sediments for analysis makes precise continental distribution during the Neoproterozoic difficult to establish.[4] Some reconstructions point towards polar continents — which have been a feature of all other major glaciations, providing a point upon which ice can nucleate. Changes in ocean circulation patterns may then have provided the trigger of snowball Earth.[5]


Additional factors that may have contributed to the onset of the Neoproterozoic Snowball include the introduction of atmospheric free oxygen, which may have reached sufficient quantities to react with methane in the atmosphere, oxidising it to carbon dioxide, a much weaker greenhouse gas,[6] and a younger — thus fainter — sun, which would have emitted 6% less radiation in the Neoproterozoic.[7] Methane is a chemical compound with the molecular formula CH4. ...


Normally, as the Earth gets colder due to natural climatic fluctuations and changes in incoming solar radiation, the cooling slows these weathering reactions. As a result, less carbon dioxide is removed from the atmosphere and the Earth warms as this greenhouse gas accumulates — this 'negative feedback' process limits the magnitude of cooling. During the Cryogenian period, however, the Earth's continents were all at tropical latitudes, which made this moderating process less effective, as high weathering rates continued on land even as the Earth cooled. This let ice advance beyond the polar regions. Once ice advanced to within 30° of the equator,[8] a positive feedback could ensue such that the increased reflectiveness (albedo) of the ice led to further cooling and the formation of more ice, until the whole Earth is ice covered. This article does not cite any references or sources. ... The Cryogenian Period (from Greek cryos ice and genesis birth) is the second geologic period of the Neoproterozoic Era, followed by the Ediacaran Period. ... A tropic is either of two circles of latitude: Tropic of Cancer, at 23½°N Tropic of Capricorn, at 23½°S Tropic is also the name of a town in Utah, United States. ... Albedo is the ratio of reflected to incident electromagnetic radiation. ...


Polar continents, due to low rates of evaporation, are too dry to allow substantial carbon deposition - restricting the amount of atmospheric carbon doxide that can be removed from the carbon cycle. A gradual rise of the proportion of the isotope carbon-13 relative to carbon-12 in sediments pre-dating "global" glaciation indicates that CO2 draw-down before snowball Earths was a slow and continuous process. [9] This article or section is in need of attention from an expert on the subject. ... Isotopes are any of the several different forms of an element each having different atomic mass (mass number). ...


The start of Snowball Earths are always marked by a sharp downturn in the δ13C value of sediments,[10] a hallmark that may be attributed to a crash in biological productivity as a result of the cold temperatures and ice-covered oceans.


During the frozen period

Global temperature fell so low that the equator was as cold as modern-day Antarctica.[11] This low temperature was maintained by the reflective ice, its high albedo resulting in most incoming solar energy being reflected back into space. A paucity of heat-retaining clouds, caused by water vapour freezing out of the atmosphere, amplified this effect. Albedo is the ratio of reflected to incident electromagnetic radiation. ...


Breaking out of global glaciation

The carbon dioxide levels necessary to unfreeze the Earth have been estimated as being 350 times what they are today, about 13% of the atmosphere.[12] Since the Earth was almost completely covered with ice, carbon dioxide could not be withdrawn from the atmosphere by the weathering of siliceous rocks. Over 4-30 million years, enough CO2 and methane, mainly emitted by volcanoes, would accumulate to finally cause enough greenhouse effect to make surface ice melt in the tropics until a band of ice-free land and water developed;[13] this would be darker than the ice, and thus absorb more energy from the sun - initiating a "positive feedback". In order to meet Wikipedias quality standards, this article requires cleanup. ... Siliceous rocks are sedimentary rocks that have silica (SiO2) as the principal constituent. ... Methane is a chemical compound with the molecular formula CH4. ... For other uses, see Volcano (disambiguation). ... Positive feedback is a feedback system in which the system responds to the perturbation in the same direction as the perturbation (It is sometimes referred to as cumulative causation). ...


On the continents, the melting of glaciers would release massive amounts of glacial deposit, which would erode and weather. The resulting sediments supplied to the ocean would be high in nutrients such as phosphorus, which combined with the abundance of CO2 would trigger a cyanobacterial population explosion, which would cause a relatively rapid reoxygenation of the atmosphere, which may have contributed to the rise of the Ediacaran biota and the subsequent Cambrian Explosion - a higher oxygen concentration allowing large multicellular lifeforms to develop. This positive feedback loop would melt the ice in geological short order, perhaps less than 1000 years; replenishment of atmospheric oxygen and depletion of the CO2 levels would take further millennia. Austrias longest glacier, the Pasterze, winds its 8 km (5 mile) route at the foot of Austrias highest mountain, the Grossglockner A glacier is a large, long-lasting river of ice that is formed on land and moves in response to gravity. ... General Name, Symbol, Number phosphorus, P, 15 Chemical series nonmetals Group, Period, Block 15, 3, p Appearance waxy white/ red/ black/ colorless Standard atomic weight 30. ... Orders The taxonomy of the Cyanobacteria is currently under revision. ... Dickinsonia costata, an Ediacaran organism of unknown affinity, with a quilted appearance. ... The Cambrian explosion is the geologically kukko sudden appearance in the fossil record of the ancestors of familiar animals, starting about 542 million years ago (Mya). ... Positive feedback is a feedback system in which the system responds to the perturbation in the same direction as the perturbation (It is sometimes referred to as cumulative causation). ... A millennium (pl. ...


It is possible that carbon dioxide levels fell enough for Earth to freeze again; this cycle may have repeated until the continents had drifted to more polar latitudes.[14] Plates in the crust of the earth, according to the plate tectonics theory Continental drift refers to the movement of the Earths continents relative to each other. ...


Evidence

Palaeomagnetism

One reconstruction of continental locations during Snowball Earth, showing where glacial deposits have been found.[1]

The Snowball Earth hypothesis was first posited in order to explain what were then considered to be glacial deposits near the equator. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ...


Since continents drift with time, ascertaining their position at a given point in history is far from trivial. In addition to considerations of how the continents would have fitted together, the latitude at which a rock was deposited can be constrained by Palæomagnetism.


When sedimentary rocks form, magnetic minerals within them tend to align themselves with the Earth's magnetic field. Through the precise measurement of this paleomagnetism, it is possible to estimate the latitude (but not the longitude) where the rock matrix was deposited. Paleomagnetic measurements have indicated that some sediments of glacial origin in the Neoproterozoic rock record were deposited within 10 degrees of the equator,[15] although the accuracy of this reconstruction is in question.[7] This palæomagnetic location of apparently glacial sediments (such as dropstones) has been taken to suggest that glaciers extended to sea-level in the tropical latitudes. It is not clear whether this can be taken to imply a global glaciation, or the existence of localised, possibly land-locked, glacial regimes.[16] Two types of sedimentary rock: limey shale overlaid by limestone. ... Paleomagnetism refers to the study of the record of the Earths magnetic field preserved in various magnetic minerals through time. ... Latitude,usually denoted symbolically by the Greek letter phi, , gives the location of a place on Earth north or south of the equator. ... Longitude is the east-west geographic coordinate measurement most commonly utilized in cartography and global navigation. ... The Neoproterozoic Era is the unit of geologic time from 1,000 to 542 +/- 0. ...


Skeptics suggest that the palæomagnetic data could be corrupted if the Earth's magnetic field was substantially different from today's. Depending on the rate of cooling of the Earth's core, it is possible that during the Proterozoic, its magnetic field did not approximate a dipolar distribution, with a North and South pole roughly aligning with the planet's axis as they do today. Instead, a hotter core may have circulated more vigorously and given rise to 4, 8 or more poles. Paleomagnetic data would then have to be re-interpreted as particles could align pointing to a 'West Pole' rather than the North Pole. Magnetic field lines shown by iron filings In physics, a magnetic field is a solenoidal vector field in the space surrounding moving electric charges and magnetic dipoles, such as those in electric currents and magnets. ... The Earths magnetic field, which is approximately a dipole. ...

Global ice sheets may have delayed or prevented the establishment of multicellular life.
Global ice sheets may have delayed or prevented the establishment of multicellular life.

Image File history File linksMetadata Download high-resolution version (937x688, 137 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Antarctica Metadata This file contains additional information, probably added from the digital camera or scanner used to create... Image File history File linksMetadata Download high-resolution version (937x688, 137 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Antarctica Metadata This file contains additional information, probably added from the digital camera or scanner used to create...

Glacial deposits at low latitudes

Sedimentary rocks that are deposited by glaciers have distinctive features that enable their identification. Long before the advent of the Snowball Earth hypothesis many Neoproterozoic sediments had been identified as having a glacial origin, including some apparently at tropical latitudes. However, there is only one "very reliable" datum point identifying tropical tillites,[15] which makes statements of equatorial ice cover somewhat presumptuous. It is worth remembering that many sedimentary features traditionally associated with glaciers can also be formed by other means.[17] Evidence includes: The Neoproterozoic Era is the unit of geologic time from 1,000 to 542 +/- 0. ...

  • Dropstones (stones dropped into marine sediments), which can be caused by glaciers or by other causes.[18]
  • Varves (annual sediment layers in periglacial lakes), which can form at higher temperatures.[19]
  • Glacial striations (formed by embedded rocks scraped against bedrock): similar striations are from time to time formed by mudflows.[20]
  • Diamictites (poorly sorted conglomerates). Originally described as glacial till, most were in fact formed by debris flows.[7]

Examples of dropstones from the Eocene, when it has been suggested that there were no ice sheets. ... Wiktionary:Varves A layer or series of layers of sediment deposited in a body of still water in one year. ... Glacial grooves caused by the Wisconsin glaciation at Kelleys Island, Ohio Glacial striations or glacial grooves are scratches or gouges cut into the bedrock by process of glacial abrasion during one of the Earths Ice Ages or by mountain glaciers. ... A mudflow or mudslide is the most rapid (up to 80 km/h) and fluid type of downhill mass wasting. ... Diamictites (IPA: ) are non-sorted conglomerates with a wide range of clasts with up to 25% gravel sized (greater than 2 mm). ... Glacial till with tufts of grass Till is an unsorted glacial sediment. ... Scars formed by debris flow in great Los Angeles during the winter of 1968-1969. ...

Open-water deposits

It appears that some deposits formed during the Snowball period could only have been formed in the presence of an active hydrological cycle. Bands of glacial deposits up to hundreds of metres thick, separated by small (metres) bands of non-glacial sediments, demonstrate that glaciers were melting and re-forming repeatedly; solid oceans would not permit this scale of deposition.[21] It is considered possible that ice streams such as seen in Antarctica today could be responsible for these sequences. Further, sedimentary features that could only form in open water, for example wave-formed ripples, far-travelled ice-rafted debris and indicators of photosynthetic activity, can be found throughout sediments dating from the 'Snowball Earth' periods. Whilst these may represent 'oases' of meltwater on a completely frozen Earth,[22] computer modelling suggests that large areas of the ocean must have remained ice-free arguing that a "hard" snowball is not plausible in terms of energy balance and general circulation models.[23] An Ice stream is a region of an ice sheet that moves significantly faster than the surrounding ice. ...


Carbon isotope ratios: reduced photosynthesis?

There are two stable isotopes of carbon in sea water: carbon-12 (C-12) and the rare carbon-13 (C-13), which makes up about 1.109% of all carbon isotopes. Isotopes are any of the several different forms of an element each having different atomic mass (mass number). ... Sea water is water from a sea or ocean. ... Carbon 12 is a stable isotope of the element carbon. ... Carbon-13 is a stable isotope of carbon. ...


Biochemical processes, of which photosynthesis is one, tend to preferentially incorporate the lighter C-12 isotope. Thus ocean-dwelling photosynthesizers, both protists and algae, tend to be very slightly depleted in C-13, relative to the abundance found in the primary volcanic sources of the Earth's carbon. Therefore, an ocean with photosynthetic life will have a higher C-12/C-13 ratio within organic remains, and a lower ratio in corresponding ocean water. The organic component of the lithified sediments will forever remain very slightly, but measurably, depleted in C-13. This article needs additional references or sources for verification. ... Typical phyla Chromista Heterokontophyta Haptophyta Cryptophyta (cryptomonads) Alveolata Dinoflagellata Apicomplexa Ciliophora (ciliates) Excavata Euglenozoa Percolozoa Metamonada Rhizaria Radiolaria Foraminifera Cercozoa Archaeplastida (in part) Rhodophyta (red algae) Glaucophyta (basal archaeplastids) Amoebozoa Choanozoa Many others; classification varies Protists (IPA: ) are a diverse group of organisms, comprising those eukaryotes that are not animals... A seaweed (Laurencia) up close: the branches are multicellular and only about 1 mm thick. ... This article is about volcanoes in geology. ...


During the proposed episode of Snowball Earth, there are variations in the concentration of C-13 that are rapid and extreme compared to observed normal modern variations.[24] This is consistent with a deep freeze that killed off most or nearly all photosynthetic life in the water. Close analysis of the timing of C-13 'spikes' in deposits across the globe allows the recognition of four, possibly five, glacial events in the late Neoproterozoic.[25]


Banded iron formations (BIF)

2.1 billion year old rock with black-band ironstone
2.1 billion year old rock with black-band ironstone

Banded iron formations are sedimentary rocks of layered iron oxide and iron-poor chert. In the presence of oxygen, iron naturally rusts and becomes insoluble in water. The banded iron formations are commonly very old and their deposition is often related to the oxidation of the Earth's atmosphere during the Paleoproterozoic era, when dissolved iron in the ocean came in contact with photosynthetically-produced oxygen and precipitated out as iron oxide. The bands were produced at the tipping point between an anoxic atmosphere and an oxygenated atmosphere. Since today's atmosphere is oxygen rich (now nearly 21% by volume), it is not possible to accumulate enough iron oxide to deposit a banded formation. The only extensive iron formations that were deposited after the Paleoproterozoic (after 1.8 billion years ago) are associated with Cryogenian glacial deposits. Image File history File links Download high resolution version (2692x1936, 1704 KB) File links The following pages link to this file: Banded iron formation Ironstone ... Image File history File links Download high resolution version (2692x1936, 1704 KB) File links The following pages link to this file: Banded iron formation Ironstone ... 2. ... Iron oxide pigment There are a number of iron oxides: Iron oxides Iron(II) oxide or ferrous oxide (FeO) The black-coloured powder in particular can cause explosions as it readily ignites. ... Chert Chert (IPA: ) is a fine-grained silica-rich cryptocrystalline sedimentary rock that may contain small fossils. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Standard atomic weight 55. ... The Paleoproterozoic is the first of the three sub-divisions of the Proterozoic occurring between 2500 to 1600 million years ago. ... The phrase tipping point or angle of repose is a sociology term that refers to that dramatic moment when something unique becomes common. ... Please wikify (format) this article as suggested in the Guide to layout and the Manual of Style. ... General Name, Symbol, Number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Standard atomic weight 15. ...


For such iron-rich rocks to be deposited there would have to be anoxia in the ocean, so much dissolved iron (as ferrous oxide) could accumulate before it met an oxidant that would precipitate it as ferric oxide. For the ocean to become anoxic it must have limited gas exchange with the oxygenated atmosphere. Proponents of the hypothesis argue that the reappearance of BIF in the sedimentary record is a result of limited oxygen levels in an ocean sealed by sea ice,[26] whilst detractors suggest that the rarity of the BIF deposits may indicate that they formed in inland seas. Being isolated from the oceans, such lakes may have been stagnant and anoxic at depth, much like today's Black Sea; a sufficient input of iron could provide the necessary conditions for BIF formation.[7] Iron(II) oxide, also called ferrous oxide, is a black-colored powder with the chemical formula FeO. It consists of the element iron in the oxidation state of 2 bonded to oxygen. ... Ferric is a term used for the iron with the oxidation number +3. ... For other uses, see Black Sea (disambiguation). ...


Cap carbonate rocks

Volcanoes may have had a role in replenishing CO2, possibly ending the global ice age that was the Snowball Earth during the Cryogenian Period.
Volcanoes may have had a role in replenishing CO2, possibly ending the global ice age that was the Snowball Earth during the Cryogenian Period.

Around the top of Neoproterozoic glacial deposits there is commonly a sharp transition into a chemically precipatated sedimentary limestone or dolostone metres to tens of metres thick.[27] These cap carbonates sometimes occur in sedimentary successions that have no other carbonate rocks, suggesting that their deposition is result of a profound aberration in ocean chemistry.[28] Image File history File links Download high-resolution version (1000x750, 58 KB) The Mahameru volcano on the island Java of Indonesia. ... Image File history File links Download high-resolution version (1000x750, 58 KB) The Mahameru volcano on the island Java of Indonesia. ... The Cryogenian Period (from Greek cryos ice and genesis birth) is the second geologic period of the Neoproterozoic Era, followed by the Ediacaran Period. ... -1... Dolostone is a sedimentary carbonate rock that contains a high percentage of the mineral dolomite. ...


These cap carbonates have unusual chemical composition, as well as strange sedimentary structures that are often interpreted as large ripples.[29] The formation of such sedimentary rocks could be caused by a large influx of positively-charged ions, as would be produced by rapid weathering during the extreme greenhouse following a Snowball Earth event. The δ13C isotopic signature of the cap carbonates is near -5‰, consistent with the value of the mantle — such a low value is usually could be taken to signify an absence of life, since photosynthesis usually acts to raise the value; alternatively the release of methane deposits could have lowered it from a higher value, and counterbalance the effects of photosynthesis. ...


The precise mechanism involved in the formation of cap carbonates is not clear, but the most cited explanation suggests that at the melting of a Snowball Earth, water would dissolve the abundant CO2 from the atmosphere to form carbonic acid, would fall as acid rain. This would weather exposed silicate and carbonate rock (including readily-attacked glacial debris), releasing large amounts of calcium, which when washed into the ocean would form distinctively textured layers of carbonate sedimentary rock. Such an abiotic "cap carbonate" sediment can be found on top of the glacial till that gave rise to the Snowball Earth hypothesis. View of Jupiters active atmosphere, including the Great Red Spot. ... Carbonic acid (ancient name acid of air or aerial acid) has the formula H2CO3. ... The term acid rain or more accurately acid precipitation is commonly used to mean the deposition of acidic components in rain, snow, dew, or dry particles. ... In chemistry, a silicate is a compound containing an anion in which one or more central silicon atoms are surrounded by electronegative ligands. ... In organic chemistry, a carbonate is a salt of carbonic acid. ... This balancing rock, Steamboat Rock stands in Garden of the Gods park in Colorado Springs, CO The rocky side of a mountain creek near Orosí, Costa Rica. ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Standard atomic weight 40. ... This article or section does not adequately cite its references or sources. ... Cap carbonates are layers of distinctively textured carbonate rocks which typically form the uppermost layer of sedimentary sequences reflecting major glaciations in the geological record. ...


However, there are some problems with the designation of a glacial origin to cap carbonates. Firstly, the high carbon dioxide concentration in the atmosphere would cause the oceans to become acidic, and dissolve any carbonates contained within - starkly at odds with the deposition of cap carbonates. Further, the thickness of some cap carbonates is far above what could reasonably be produced in the relatively quick deglaciations. The cause is further weakened by the lack of cap carbonates above many sequences of clear glacial origin at a similar time.[7]


Changing acidity

Isotopes of the element boron suggest that the pH of the oceans dropped dramatically before and after the Marinoan snowball event.[30] This may indicate a build up of carbon dioxide in the atmosphere, some of which would dissolve into the oceans to form carbonic acid. Although the boron variations may be evidence of extreme climate change they need not imply a global glaciation. General Name, Symbol, Number boron, B, 5 Chemical series metalloids Group, Period, Block 13, 2, p Appearance black/brown Standard atomic weight 10. ... The correct title of this article is . ... Carbonic acid (ancient name acid of air or aerial acid) has the formula H2CO3. ...


Space dust

The Earth's surface is very depleted in the element Iridium, which primarily resides in the Earth's core. The only significant source of the element at the surface is cosmic particles that reach Earth. During a Snowball Earth, Iridium would accumulate on the ice sheets, and when the ice melted the resulting layer of sediment would be rich in Iridium. An Iridium anomaly has been discovered at the base of the cap carbonate formations, and has been used to suggest that the glacial episode lasted for at least 3 million years,[31] but this does not necessarily imply a global extent to the glaciation; indeed a similar anomaly could be explained by the impact of a large extra-planetary object, such a meteor.[32] This article is about the chemical element. ... Earth, also known as the Earth or Terra, is the third planet outward from the Sun. ... Cosmogenic refers to rare radioactive isotopes created when cosmic radiation interacts with an atomic nucleus. ... The term bolide (from the Greek βολις, bolis, missile) can refer to either an extraterrestrial body that collides with the Earth, or to an exceptionally bright, fireball-like meteor regardless of whether it ultimately impacts the surface. ... Photo of a burst of meteors with extended exposure time A meteor is the visible path of a meteoroid that enters the Earths (or another bodys) atmosphere, commonly called a shooting star or falling star. ...


Cyclic climate fluctuations

Using the ratio of mobile cations to those that remain in soils during chemical weathering (the chemical index of alteration), it has been shown that chemical weathering varied in a cyclic fashion within a glacial succession, increasing during interglacial periods and decreasing during cold and arid glacial periods.[33] This pattern, if a true reflection of events, suggests that the "snowball Earths" bore a stronger resemblance to Pleistocene ice age cycles than to a completely frozen Earth. A cation is an ion with positive charge. ... This is a drainage basin developed in response to a steady rate of lowering of the local base level, which is the lower boundary. ... There have been four major periods of glaciation in the Earths past. ... Variations in CO2, temperature and dust from the Vostok ice core over the last 400 000 years For the animated movie, see Ice Age (movie). ...


Opposing the hypothesis

"Zipper rift" hypothesis

Some plaudits suggest that the Neoproterozoic Snowball Earth was in fact no different from any other glaciation in Earth's history. Eyles and Januszczak[7] recognise that efforts to find a single cause are likely to end in failure, and posit a "preeminent" controller. They contend that two pulses of continental "unzipping" — first, the breakup of the supercontinent Rodinia, forming the proto-Pacific ocean; then the splitting of the continent Baltica from Laurentia, forming the proto-Atlantic — coincided with the glaciated periods. The associated tectonic uplift would form high plateaus, just as the East African rift is responsible for high topography; this high ground could then host glaciers. Banded iron formations have been taken as unavoidable evidence for global ice cover, since they require dissolved iron ions and anoxic waters to form; however, the limited extent of the Neoproterozoic banded iron deposits means that they may not have formed in frozen oceans, but instead in inland seas. Such seas can experience a wide range of chemistries; high rates of evaporation could concentrate iron ions, and a periodic lack of circulation could allow anoxic bottom water to form. Continental rifting, with associated subsidence, tends to produce such landlocked water bodies. This rifting, and associated subsidence, would produce the space for the fast deposition of sediments, negating the need for an immense and rapid melting to raise the global sea levels. Depiction of Rodinia at time of initial breakup. ... Baltica (green) Baltica is a Late Proterozoic-Early Palaeozoic continent that now includes the East European craton of northwestern Eurasia. ... This article or section does not adequately cite its references or sources. ... This article does not cite any references or sources. ...


High-obliquity hypothesis

A competing theory to explain the presence of ice on the equatorial continents was that the Earth's axial tilt was quite high, in the vicinity of 60°, which would place the Earth's land in high "latitudes", although supporting evidence is scarce.[34] A less extreme possibility would be that it was merely the Earth's magnetic pole that wandered to this inclination, as the magnetic readings which suggested ice-filled continents depends on the magnetic and rotational poles being relatively similar (there is some evidence[citation needed] to believe that this is the case). In either of these two situations, the freeze would be limited to relatively small areas, as is the case today; severe changes to the Earth's climate are not necessary. In astronomy, Axial tilt is the inclination angle of a planets rotational axis in relation to a perpendicular to its orbital plane. ... Magnetic lines of force of a bar magnet shown by iron filings on paper A magnet is an object that has a magnetic field. ...


Inertial interchange true polar wander

The evidence for low latitude glacial deposits during the supposed Snowball Earth episodes has been reinterpreted via the concept of inertial interchange true polar wander (IITPW).[35][36] This theory, created to explain palæomagnetic data, suggests that the continents drifted far faster during the late Neoproterozoic, allowing glacial deposits to form at the poles before continents returned to the equator, when palæomagnetic beds were laid down. Whilst the physics behind the proposition is sound, the removal of one flawed data point from the original study rendered the application of the concept in these circumstances unwarranted.[37] Plates in the crust of the earth, according to the plate tectonics theory Continental drift refers to the movement of the Earths continents relative to each other. ...


Survival of life through frozen periods

A black smoker, a type of hydrothermal vent
A black smoker, a type of hydrothermal vent

A tremendous glaciation would curtail plant life on Earth, thus letting the atmospheric oxygen be drastically depleted and perhaps even disappear, and thus allow non-oxidized iron-rich rocks to form. Detractors argue that this kind of glaciation would have made life extinct entirely; however, microfossils such as stromatolites and oncolites prove that in shallow marine environments at least, life did not suffer any perturbation, but that trophic complexity survived the cold period unscathed.[38] Proponents counter that it may have been possible for life to survive in these ways: Image File history File links Download high resolution version (1220x1804, 532 KB) en: Black smoker at a mid-ocean ridge hydrothermal vent de: Black Smoker im Atlantischen Ozean Taken from http://www. ... Image File history File links Download high resolution version (1220x1804, 532 KB) en: Black smoker at a mid-ocean ridge hydrothermal vent de: Black Smoker im Atlantischen Ozean Taken from http://www. ... A black smoker in the Atlantic Ocean Black smokers are a type of hydrothermal vent found on the ocean floor. ... Pre-Cambrian stromatolites in the Siyeh Formation, Glacier National Park. ... There are very few or no other articles that link to this one. ...

  • Reservoirs of anaerobic and low-oxygen life powered by chemicals in deep oceanic hydrothermal vents surviving in Earth's deep oceans and crust; but photosynthesis would not have been possible there.
  • In deep ocean regions far from the supercontinent Rodinia or its remnants as it broke apart and drifted on the tectonic plates, which may have allowed for some small regions of open water preserving small quantities of life with access to light and CO2 for photosynthesizers (not multicellular plants, which did not yet exist) to generate traces of oxygen that were enough to sustain some oxygen-dependent organisms. This would happen even if the sea froze over completely if small parts of the ice were thin enough to admit light.
  • In nunatak areas in the tropics, where daytime tropical sun or volcanic heat heated bare rock sheltered from cold wind and made small temporary melt pools, which would freeze over at sunset.
  • As eggs and dormant cells and spores deep-frozen into ice right through the worst phases of the frozen period.
  • Under the ice layer, in chemolithotrophic (mineral-metabolizing) ecosystems theoretically resembling those in existence in modern glacier beds, high-alpine and Arctic talus permafrost, and basal glacial ice. This is especially plausible in areas of volcanism or geothermal activity.[39]
  • In pockets of liquid water within and under the ice caps, similar to Lake Vostok in Antarctica. In theory, this system may resemble microbial communities living in the perennially frozen lakes of the Antarctic dry valleys. Photosynthesis can occur under up to 100 m of ice, and at the temperatures predicted by models equatorial sublimation would prevent equatorial ice thickness from exceeding 10 m.[40]
  • In small oases of molten water, as would be found near geothermal hotspots resembling Iceland today.[41]

However, organisms and ecosystems, as far as it can be determined by the fossil record, do not appear to have undergone the significant change that would be expected by a mass extinction; even if life were to cling on in all the refugia listed above, the post-Snowball biota would have a noticeably different diversity and composition, something that is not observed.[42] In fact, the organisms which ought to be most susceptible to climatic variation emerge unscathed from the Snowball Earth.[32] Aerobic and anaerobic bacteria can be identified by growning them in liquid culture: 1: Obligate aerobic bacteria gather at the top of the test tube in order to absorb maximal amount of oxygen. ... A hydrothermal vent A hydrothermal vent is a fissure in a planets surface from which geothermally heated water issues. ... Earth cutaway from core to exosphere. ... This article needs additional references or sources for verification. ... In geology, a supercontinent is a land mass comprising more than one continental core, or craton. ... Depiction of Rodinia at time of initial breakup. ... The tectonic plates of the world were mapped in the second half of the 20th century. ... Nunataks on Greenlands east coast This article is about the geographic feature. ... A tropic is either of two circles of latitude: Tropic of Cancer, at 23½°N Tropic of Capricorn, at 23½°S Tropic is also the name of a town in Utah, United States. ... It has been suggested that this article or section be merged with Lithoautotroph. ... A coral reef near the Hawaiian islands is an example of a complex marine ecosystem. ... This article is about volcanoes in geology. ... Earth cutaway from core to exosphere. ... Lake Vostoks location within Antarctica (NASA) Lake Vostok is the largest of more than 70 subglacial lakes in Antarctica. ... A microorganism or microbe is an organism that is so small that it is microscopic (invisible to the naked eye). ... Sublimation has three separate meanings: Sublimation (physics), the change from solid to gas without passing the liquid state Sublimation (psychology), the transformation of emotions Dye sublimation, the transference of printed images to a synthetic substrate by the application of heat Category: ... Earth cutaway from core to exosphere. ... HotSpot is the primary Java Virtual Machine for desktops and servers produced by Sun Microsystems. ...


Evolution of life

Dickinsonia costata, an Ediacaran organism of unknown affinity, with a quilted appearance.

The Neoproterozoic was a time of remarkable diversification of multicellular organisms, including animals. Organism size and complexity increased considerably after the end of the Snowball glaciations. This development of multicellular organisms may have been the result of increased evolutionary pressures resulting from multiple icehouse-hothouse cycles; in this sense, Snowball Earth episodes may have "pumped" evolution. Alternatively, fluctuating nutrient levels and rising oxygen may have played a part. Interestingly, another major glacial episode may have ended just a few million years before the Cambrian Explosion. Image File history File linksMetadata Size of this preview: 800 × 600 pixel Image in higher resolution (2272 × 1704 pixel, file size: 1. ... Image File history File linksMetadata Size of this preview: 800 × 600 pixel Image in higher resolution (2272 × 1704 pixel, file size: 1. ... Species Dickinsonia is an ancient ovoid fossil with somewhat radial tubes from a (sometimes missing) central ridge. ... The Neoproterozoic Era is the unit of geologic time from 1,000 to 542 +/- 0. ... The Cambrian explosion is the geologically kukko sudden appearance in the fossil record of the ancestors of familiar animals, starting about 542 million years ago (Mya). ...


Origins of the hypothesis

Sir Douglas Mawson, an Australian geologist and Antarctic explorer, spent much of his career studying the Neoproterozoic stratigraphy of South Australia where he identified thick and extensive glacial sediments and late in his career speculated on the possibility of global glaciation.[43] Mawson's ideas of global glaciation, however, were based on the mistaken assumption that the geographic position of Australia, and that of other continents where low-latitude glacial deposits are found, has remained constant through time. With the advancement of the continental drift hypothesis, and eventually plate tectonic theory, came an easier explanation for the glaciogenic sediments — they were deposited at a point in time when the continents were at higher latitudes. In 1964 the idea of global-scale glaciation reemerged when W. Brian Harland published a paper in which he presented paleomagnetic data showing that glacial tillites in Svalbard and Greenland were deposited at tropical latitudes.[44] From this paleomagnetic data, and the sedimentological evidence that the glacial sediments interrupt successions of rocks commonly associated with tropical to temperate latitudes, he argued for an ice age that was so extreme that it resulted in the deposition of marine glacial rocks in the tropics. Sir Douglas Mawson (May 5, 1882-1958) was Australian Antarctic explorer. ... The Neoproterozoic Era is the unit of geologic time from 1,000 to 542 +/- 0. ... Plates in the crust of the earth, according to the plate tectonics theory Continental drift refers to the movement of the Earths continents relative to each other. ... The tectonic plates of the world were mapped in the second half of the 20th century. ... W. Brian Harland (1917 - 2003) was an eminent geologist at Cambridge University, England. ... Paleomagnetism refers to the orientation of the Earths magnetic field as it is preserved in various magnetic iron bearing minerals throughout time. ...


In the 1960s, Mikhail Budyko, a Russian climatologist, developed a simple energy-balance climate model to investigate the effect of ice cover on global climate. Using this model, Budyko found that if ice sheets advanced far enough out of the polar regions a feedback ensued where the increased reflectiveness (albedo) of the ice lead to further cooling and the formation of more ice until the entire Earth was covered in ice and stabilized in a new ice-covered equilibrium.[45] . While Budyko's model showed that this ice-albedo stability could happen, he concluded that it had never happened, because his model offered no way to escape from such a scenario. Mikhail Ivanovich Budyko (Μ.И. Будыко) (1920- ) - Russian climatologist born in Gomel, now Belarus. ... Albedo is the ratio of reflected to incident electromagnetic radiation. ...


The term "Snowball Earth" was coined by Joseph Kirschvink, a professor of geobiology at the California Institute of Technology, in a short paper published in 1992 within a lengthy volume concerning the biology of the Proterozoic eon. [26] The major contributions from this work were: (1) the recognition that the presence of banded iron formations is consistent with such a glacial episode and (2) the introduction of a mechanism with which to escape from an ice-covered Earth — the accumulation of CO2 from volcanic outgassing leading to a ultra-greenhouse effect. The California Institute of Technology (commonly referred to as Caltech)[1] is a private, coeducational university located in Pasadena, California, in the United States. ... The Proterozoic (IPA: ) is a geological eon representing a period before the first abundant complex life on Earth. ... 2. ...


Interest in the Snowball Earth increased dramatically after Paul F. Hoffman, the Sturgis Hooper professor of geology at Harvard University, and coauthors applied Kirschvink's ideas to a succession of Neoproterozoic sediments in Namibia, elaborated upon the hypothesis by incorporating such observations as the occurrence of cap carbonates, and published their results in the journal Science.[46] Paul F. Hoffman is a Sturgis Hooper Professor of Geology at Harvard University. ... Harvard University (incorporated as The President and Fellows of Harvard College) is a private university in Cambridge, Massachusetts, USA and a member of the Ivy League. ...


Currently, aspects of the hypothesis remain controversial and it is being debated under the auspices of the International Geoscience Programme (IGCP) Project 512: Neoproterozoic Ice Ages.[47]


Other suspected Snowball Earths

Paleoproterozoic

The Snowball Earth hypothesis has been invoked to explain glacial deposits in the Huronian supergroup of Canada though the paleomagnetic evidence that suggests ice sheets at low latitudes is contested.[48][49] The glacial sediments of the Makganyene formation of South Africa are slightly younger than the Huronian glacial deposits (~2.25 billion years old) and were deposited at tropical latitudes.[50] It has been proposed that rise of free oxygen that occurred during this part of the Paleoproterozoic removed methane in the atmosphere through oxidation. As the Sun was notably weaker at the time, the Earth's climate could have been relied on methane, a powerful greenhouse gas, to maintain surface temperatures above freezing. In the absence of this methane greenhouse, temperatures plunged and a snowball event could have occurred.[49] The Huronian glaciation was from 2400 mya to 2100 mya, during the Siderian and Rhyacian periods of the Paleoproterozoic era. ... The Paleoproterozoic is the first of the three sub-divisions of the Proterozoic occurring between 2500 to 1600 million years ago. ... The Sun (Latin: Sol) is the star at the center of the Solar System. ...


Karoo Ice Age (early guess)

Discovery of Carboniferous Age glacial deposits in areas such as India and South America which are now tropical, led to early guesses that the Karoo Ice Age glaciation reached into the tropics, until discovery of continental drift showed that all the affected areas had been grouped together close around the south pole as the supercontinent of Gondwanaland. The Carboniferous is a major division of the geologic timescale that extends from the end of the Devonian period, about 359. ... South America South America is a continent crossed by the equator, with most of its area in the Southern Hemisphere. ... The Karoo Ice Age from 350-250 million years ago was the second major period of Glaciation of the Phanerozoic Era. ... Plates in the crust of the earth, according to the plate tectonics theory Continental drift refers to the movement of the Earths continents relative to each other. ... In geology, a supercontinent is a land mass comprising more than one continental core, or craton. ... This article is about the ancient supercontinent of Gondwana. ...


Notes and references

  1. ^ a b Reprinted by permission from Macmillan Publishers Ltd: Nature 405:425-429, copyright 2000. See Hyde et al (2000).
  2. ^ Kirschvink, J.L. (1992). "Late Proterozoic low-latitude global glaciation: The snowball Earth", in Schopf, JW, and Klein, C.: The Proterozoic Biosphere: A Multidisciplinary Study. Cambridge University Press, Cambridge, 51-52. 
  3. ^ Jacobsen, S.B. (2001). "Earth science. Gas hydrates and deglaciations.". Nature 412 (6848): 691-3. DOI:10.1038/35089168. Retrieved on 2007-05-21. 
  4. ^ Meert, J.G.; Torsvik, T.H. (2004). "Paleomagnetic Constraints on Neoproterozoic ‘Snowball Earth’Continental Reconstructions". GS Jenkins, MAS McMenamin, CP McKey, CP and L. Sohl (Editors), The Extreme Proterozoic: Geology, Geochemistry, and Climate. American Geophysical Union Geophysical Monograph 146: 5-11. Retrieved on 2007-05-06. 
  5. ^ Smith, A.G.; Pickering, K.T. (2003). "Oceanic gateways as a critical factor to initiate icehouse Earth". Journal of the Geological Society 160 (3): 337-340. DOI:10.1144/0016-764902-115. Retrieved on 2007-04-26. 
  6. ^ Kerr, R.A. (1999). "Early life thrived despite earthly travails.". Science 284 (5423): 2111-3. Retrieved on 2007-05-05. 
  7. ^ a b c d e f Eyles, N.; Januszczak, N. (2004). "’Zipper-rift’: A tectonic model for Neoproterozoic glaciations during the breakup of Rodinia after 750 Ma". Earth-Science Reviews 65 (1-2): 1-73. Retrieved on 2007-05-04. 
  8. ^
  9. ^ Schrag, D.P.; Berner, R.A., Hoffman, P.F., Halverson, G.P. (2002). "On the initiation of a snowball Earth". Geochem. Geophys. Geosyst 3 (10.1029). Retrieved on 2007-02-28. 
  10. ^ Hoffman, P.F.; Kaufman, A.J., Halverson, G.P., Schrag, D.P. (1998-08-28). "A Neoproterozoic Snowball Earth". Science 281 (5381): 1342. DOI:10.1126/science.281.5381.1342. Retrieved on 2007-05-04. 
  11. ^ Hyde, W.T.; Crowley, T.J., Baum, S.K., Peltier, W.R. (2000). "Neoproterozoic 'snowball Earth' simulations with a coupled climate/ice-sheet model". Nature 405 (6785): 425-429. Retrieved on 2007-05-05. 
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A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 124th day of the year (125th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 125th day of the year (126th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 125th day of the year (126th in leap years) in the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... ISSN, or International Standard Serial Number, is the unique eight-digit number applied to a periodical publication including electronic serials. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 149th day of the year (150th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 119th day of the year (120th in leap years) in the Gregorian calendar. ... Year 1995 (MCMXCV) was a common year starting on Sunday (link will display full 1995 Gregorian calendar). ... is the 32nd day of the year in the Gregorian calendar. ... This article or section does not adequately cite its references or sources. ... In geology, a supercontinent is a land mass comprising more than one continental core, or craton. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... April 27 is the 117th day of the year (118th in leap years) in the Gregorian calendar, with 248 days remaining. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 125th day of the year (126th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... April 27 is the 117th day of the year (118th in leap years) in the Gregorian calendar, with 248 days remaining. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... April 27 is the 117th day of the year (118th in leap years) in the Gregorian calendar, with 248 days remaining. ... Year 1995 (MCMXCV) was a common year starting on Sunday (link will display full 1995 Gregorian calendar). ... is the 335th day of the year (336th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... April 27 is the 117th day of the year (118th in leap years) in the Gregorian calendar, with 248 days remaining. ... Year 1996 (MCMXCVI) was a leap year starting on Monday (link will display full 1996 Gregorian calendar). ... is the 60th day of the year (61st in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... April 27 is the 117th day of the year (118th in leap years) in the Gregorian calendar, with 248 days remaining. ... Also see: 2002 (number). ... is the 1st day of the year in the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 124th day of the year (125th in leap years) in the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 125th day of the year (126th in leap years) in the Gregorian calendar. ... Year 1997 (MCMXCVII) was a common year starting on Wednesday (link will display full 1997 Gregorian calendar). ... June 24 is the 175th day of the year (176th in leap years) in the Gregorian calendar, with 190 days remaining. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 126th day of the year (127th in leap years) in the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... ISSN, or International Standard Serial Number, is the unique eight-digit number applied to a periodical publication including electronic serials. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 124th day of the year (125th in leap years) in the Gregorian calendar. ... Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... April 8 is the 98th day of the year (99th in leap years) in the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 124th day of the year (125th in leap years) in the Gregorian calendar. ... Year 2003 (MMIII) was a common year starting on Wednesday of the Gregorian calendar. ... is the 121st day of the year (122nd in leap years) in the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 149th day of the year (150th in leap years) in the Gregorian calendar. ... Year 1997 (MCMXCVII) was a common year starting on Wednesday (link will display full 1997 Gregorian calendar). ... is the 206th day of the year (207th in leap years) in the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 125th day of the year (126th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 126th day of the year (127th in leap years) in the Gregorian calendar. ... Year 1998 (MCMXCVIII) was a common year starting on Thursday (link will display full 1998 Gregorian calendar). ... is the 2nd day of the year in the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 125th day of the year (126th in leap years) in the Gregorian calendar. ... Year 2003 (MMIII) was a common year starting on Wednesday of the Gregorian calendar. ... is the 105th day of the year (106th in leap years) in the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 179th day of the year (180th in leap years) in the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 125th day of the year (126th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 125th day of the year (126th in leap years) in the Gregorian calendar. ...

Further reading

  • Gabrielle Walker (2003). Snowball Earth. Bloomsbury Publishing. ISBN 0-7475-6433-7. 

References

  • Roberts, J.D., 1971.Late Precambrian glaciation: an anti-greenhouse effect? Nature, 234, 216-217.
  • Roberts, J.D., 1976. Late Precambrian dolomites, Vendian glaciation, and the synchroneity of Vendian glaciation, J. Geology, 84, 47-63.
  • A review paper, available without subscription: Sankaran, A.V. (2003). "Neoproterozoic "snowball earth" and the "cap" carbonate controversy". Current Science 84 (7): 871. Retrieved on 2007-05-06. 
  • Torsvik, T.H. and Rehnström, E.F., 2001. Cambrian paleomagnetic data from Baltica: Implications for true polar wander and Cambrian paleogeography, J. Geol. Soc. Lond., 158, 321-329.

Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 126th day of the year (127th in leap years) in the Gregorian calendar. ...

External links


  Results from FactBites:
 
Snowball Earth - Wikipedia, the free encyclopedia (2148 words)
Geological formations which "Snowball Earth" proponents point to as evidence of the hypothesis are iron-rich rocks like taconite deposits and carbonate cap rocks.
The association of the Snowball Earth event with the Cambrian explosion (the sudden appearance of multicellular lifeforms between 570 and 530 million years ago) is also of great interest.
An even less severe possibility would be that it was merely the Earth's magnetic pole that wandered to this inclination, as the magnetic readings which suggested ice-filled continents depends on the magnetic and rotational poles being relatively similar (there is some evidence to believe that this is the case).
Snowball Earth (4762 words)
A snowball earth would be not only the most severe conceivable ice age, it would be the most prolonged” (Hoffman and Schrag 2000, p.
The Sturtian snowball period is shortly succeeded by the earliest unambiguous record of metazoan animals and, after an additional 170 Ma and two more low-latitude glaciations, by the appearance of shelly Cambrian faunas.
Overall, the various snowball earth hypotheses have potential to explain diverse observations of the Proterozoic geological record: synchronous low latitude diamictites associated with carbonate deposits, carbon isotope excursions, banded iron formations, and so on.
  More results at FactBites »

 
 

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