The Karoo
Ice AgeThe general term "ice age" or, more precisely, "glacial age" denotes a geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in an expansion of continental ice sheets, polar ice sheets and alpine glaciers. Within a long-term ice age, individual...
from 360–260
MaAnnum is a form of the Latin noun annus meaning year, from which are derived words such as annual and annuity. Annum is the accusative singular of the 2nd declension masculine noun annus , anni...
(million years ago) was the second major period of glaciation of the
PhanerozoicThe Phanerozoic eon is the current eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 545 million years and goes back to the time when diverse hard-shelled animals first appeared...
EonEon is the US English variant of the traditional aeon, which means "age" or "forever".A geologic eon is the largest division of time in geology, and is generally considered to be around a billion years.Eon or EON may also refer to:...
. It is named after the glacial
tillthumb|right|Glacial till with tufts of grassTill is unsorted glacial sediment. Glacial drift is a general term for the coarsely graded and extremely heterogeneous sediments of glacial origin. Glacial till is that part of glacial drift which was deposited directly by the glacier. It may vary from...
s found in the
KarooThe Karoo is a semi-desert region of South Africa. It has two main sub-regions - the Great Karoo in the north and the Little Karoo in the south. The 'High' Karoo is one of the distinct physiographic provinces of the larger South African Platform division.-Great Karoo:The Great Karoo has an area of...
region of
South AfricaThe Republic of South Africa is a country located at the southern tip of Africa, with a coastline on the Atlantic and Indian Oceans. To the north lie Namibia, Botswana and Zimbabwe, to the east are Mozambique and Swaziland, while Lesotho is an independent country surrounded by South Africa.Modern...
where evidence for this ice age was first clearly identified.
The
tectonicTectonic Plates is a 1992 independent Canadian film directed by Peter Mettler. Mettler also wrote the screenplay based on the play by Robert Lepage. The film stars Marie Gignac, Céline Bonnier and Robert Lepage.-Plot summary:...
assembly of the continents of
EuramericaEuramerica was a minor supercontinent created in the Devonian as the result of a collision between the Laurentian, Baltica and Avalonia cratons .Euramerica became a part of the major supercontinent Pangaea in the Permian...
(later with the
Uralian orogenyThe Uralian orogeny refers to the long series of mountain building events that raised the Ural Mountains, starting in the Late Carboniferous and Permian periods of the Palaeozoic Era, ca. 318-299 and 299-251 Mya, and ending with the last series of continental collisions in Triassic to early...
, into
LaurasiaLaurasia was a supercontinent that most recently existed as a part of the split of the Pangaea supercontinent in the late Mesozoic era. It included most of the landmasses which make up today's continents of the northern hemisphere, chiefly Laurentia , Baltica, Siberia, Kazakhstania, and the North...
) and Gondwanaland into
PangaeaPangaea, Pangæa, or Pangea was the supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago, before the component continents were separated into their current configuration.The name was first used by the German originator of the continental...
, in the Hercynian-Alleghany
OrogenyOrogeny refers to natural mountain building, and may be studied as a tectonic structural event, as a geographical event, and a chronological event...
, made a major continental landmass within the Antarctic region, and the closure of the
Rheic OceanThe Rheic Ocean was a Paleozoic ocean between the large continent Gondwana to the south and the microcontinents Avalonia and others to the north...
and
Iapetus OceanThe Iapetus Ocean was an ocean that existed in the Neoproterozoic and Paleozoic eras of the geologic timescale . The Iapetus Ocean was situated in the southern hemisphere, between the paleocontinents of Laurentia, Baltica and Avalonia...
saw disruption of warm water currents in the
PanthalassaPanthalassa , also known as the Panthalassic Ocean, was the vast global ocean that surrounded the supercontinent Pangaea, during the late Paleozoic and the early Mesozoic years. It included the Pacific Ocean to the west and north and the Tethys Ocean to the southeast...
Ocean and
Paleotethys SeaThe Tethys Ocean was an ocean that existed between the continents of Gondwana and Laurasia during the Mesozoic era before the opening of the Indian Ocean.-Modern theory:...
, which led to progressive cooling of summers, and the snowfields accumulating in winters, causing mountainous alpine
glacierA glacier is a perennial mass of ice which moves over land. A glacier forms in locations where the mass accumulation of snow and ice exceeds ablation over many years...
s to grow, and then spread out of highland areas, making
continental glacierContinental Glacier is located in Bridger-Teton and Shoshone National Forests, in the U.S. state of Wyoming and straddles the Continental Divide in the northern Wind River Range. Continental Glacier is in both the Bridger and Fitzpatrick Wildernesses, and is part of the largest grouping of glaciers...
s which spread to cover much of Gondwanaland.
At least two major periods of glaciation have been discovered:-
- The first glacial period was associated with the Mississippian era (359.2–318.1 Ma
Annum is a form of the Latin noun annus meaning year, from which are derived words such as annual and annuity. Annum is the accusative singular of the 2nd declension masculine noun annus , anni...
): ice sheets expanded from a core in southern Africa and South America.
- The second glacial period was associated with the Pennsylvanian
The Pennsylvanian is in the ICS geologic timescale the youngest subperiod or upper subsystem of the Carboniferous period. It lasted from roughly to Ma . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the...
era (318.1–299 Ma); ice sheets expanded from a core in AustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the continental mainland , the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans...
and IndiaIndia, officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the south, the Arabian Sea on the west, and the Bay of Bengal...
.
The extent of glaciation in
Antarctica| style="border-top:solid 1px #ccd2d9; padding:0.4em 1em 0.4em 0; vertical-align:top;" | 14,000,000 km
2 280,000 km
2 13,720,000 km
2 |-! style="border-top: solid 1px #ccd2d9; padding: 0.4em 1em 0.4em 0; vertical-align: top;...
is not exactly known, due to its present ice sheet.
It is thought that the shift in glacial expansion cores is due to polar wandering and tectonic movements of Pangaea.
It is thought that the evolution of land plants with the onset of the Devonian period, began a long term increase in planetary
oxygenOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
levels.
The Karoo
Ice AgeThe general term "ice age" or, more precisely, "glacial age" denotes a geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in an expansion of continental ice sheets, polar ice sheets and alpine glaciers. Within a long-term ice age, individual...
from 360–260
MaAnnum is a form of the Latin noun annus meaning year, from which are derived words such as annual and annuity. Annum is the accusative singular of the 2nd declension masculine noun annus , anni...
(million years ago) was the second major period of glaciation of the
PhanerozoicThe Phanerozoic eon is the current eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 545 million years and goes back to the time when diverse hard-shelled animals first appeared...
EonEon is the US English variant of the traditional aeon, which means "age" or "forever".A geologic eon is the largest division of time in geology, and is generally considered to be around a billion years.Eon or EON may also refer to:...
. It is named after the glacial
tillthumb|right|Glacial till with tufts of grassTill is unsorted glacial sediment. Glacial drift is a general term for the coarsely graded and extremely heterogeneous sediments of glacial origin. Glacial till is that part of glacial drift which was deposited directly by the glacier. It may vary from...
s found in the
KarooThe Karoo is a semi-desert region of South Africa. It has two main sub-regions - the Great Karoo in the north and the Little Karoo in the south. The 'High' Karoo is one of the distinct physiographic provinces of the larger South African Platform division.-Great Karoo:The Great Karoo has an area of...
region of
South AfricaThe Republic of South Africa is a country located at the southern tip of Africa, with a coastline on the Atlantic and Indian Oceans. To the north lie Namibia, Botswana and Zimbabwe, to the east are Mozambique and Swaziland, while Lesotho is an independent country surrounded by South Africa.Modern...
where evidence for this ice age was first clearly identified.
The
tectonicTectonic Plates is a 1992 independent Canadian film directed by Peter Mettler. Mettler also wrote the screenplay based on the play by Robert Lepage. The film stars Marie Gignac, Céline Bonnier and Robert Lepage.-Plot summary:...
assembly of the continents of
EuramericaEuramerica was a minor supercontinent created in the Devonian as the result of a collision between the Laurentian, Baltica and Avalonia cratons .Euramerica became a part of the major supercontinent Pangaea in the Permian...
(later with the
Uralian orogenyThe Uralian orogeny refers to the long series of mountain building events that raised the Ural Mountains, starting in the Late Carboniferous and Permian periods of the Palaeozoic Era, ca. 318-299 and 299-251 Mya, and ending with the last series of continental collisions in Triassic to early...
, into
LaurasiaLaurasia was a supercontinent that most recently existed as a part of the split of the Pangaea supercontinent in the late Mesozoic era. It included most of the landmasses which make up today's continents of the northern hemisphere, chiefly Laurentia , Baltica, Siberia, Kazakhstania, and the North...
) and Gondwanaland into
PangaeaPangaea, Pangæa, or Pangea was the supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago, before the component continents were separated into their current configuration.The name was first used by the German originator of the continental...
, in the Hercynian-Alleghany
OrogenyOrogeny refers to natural mountain building, and may be studied as a tectonic structural event, as a geographical event, and a chronological event...
, made a major continental landmass within the Antarctic region, and the closure of the
Rheic OceanThe Rheic Ocean was a Paleozoic ocean between the large continent Gondwana to the south and the microcontinents Avalonia and others to the north...
and
Iapetus OceanThe Iapetus Ocean was an ocean that existed in the Neoproterozoic and Paleozoic eras of the geologic timescale . The Iapetus Ocean was situated in the southern hemisphere, between the paleocontinents of Laurentia, Baltica and Avalonia...
saw disruption of warm water currents in the
PanthalassaPanthalassa , also known as the Panthalassic Ocean, was the vast global ocean that surrounded the supercontinent Pangaea, during the late Paleozoic and the early Mesozoic years. It included the Pacific Ocean to the west and north and the Tethys Ocean to the southeast...
Ocean and
Paleotethys SeaThe Tethys Ocean was an ocean that existed between the continents of Gondwana and Laurasia during the Mesozoic era before the opening of the Indian Ocean.-Modern theory:...
, which led to progressive cooling of summers, and the snowfields accumulating in winters, causing mountainous alpine
glacierA glacier is a perennial mass of ice which moves over land. A glacier forms in locations where the mass accumulation of snow and ice exceeds ablation over many years...
s to grow, and then spread out of highland areas, making
continental glacierContinental Glacier is located in Bridger-Teton and Shoshone National Forests, in the U.S. state of Wyoming and straddles the Continental Divide in the northern Wind River Range. Continental Glacier is in both the Bridger and Fitzpatrick Wildernesses, and is part of the largest grouping of glaciers...
s which spread to cover much of Gondwanaland.
At least two major periods of glaciation have been discovered:-
- The first glacial period was associated with the Mississippian era (359.2–318.1 Ma
Annum is a form of the Latin noun annus meaning year, from which are derived words such as annual and annuity. Annum is the accusative singular of the 2nd declension masculine noun annus , anni...
): ice sheets expanded from a core in southern Africa and South America.
- The second glacial period was associated with the Pennsylvanian
The Pennsylvanian is in the ICS geologic timescale the youngest subperiod or upper subsystem of the Carboniferous period. It lasted from roughly to Ma . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the...
era (318.1–299 Ma); ice sheets expanded from a core in AustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the continental mainland , the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans...
and IndiaIndia, officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the south, the Arabian Sea on the west, and the Bay of Bengal...
.
The extent of glaciation in
Antarctica| style="border-top:solid 1px #ccd2d9; padding:0.4em 1em 0.4em 0; vertical-align:top;" | 14,000,000 km
2 280,000 km
2 13,720,000 km
2 |-! style="border-top: solid 1px #ccd2d9; padding: 0.4em 1em 0.4em 0; vertical-align: top;...
is not exactly known, due to its present ice sheet.
It is thought that the shift in glacial expansion cores is due to polar wandering and tectonic movements of Pangaea.
Causes of the Karoo Ice Age
It is thought that the evolution of land plants with the onset of the Devonian period, began a long term increase in planetary
oxygenOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
levels. Large tree ferns, growing to 20 meters high, were secondary dominant to the large arborescent Lycopods (30-40 metres high) of the
CarboniferousThe Carboniferous is a geologic period and system that extends from the end of the Devonian period, about 359.2 ± 2.5 Ma , to the beginning of the Permian period, about 299.0 ± 0.8 Ma ....
coal forestThe Coal Forests is an informal term referring to the vast swathe of wetland forests that extended over much of the tropical land areas during Late Carboniferous and Permian times. These forests got their name because they accumulated enormous deposits of peat which later changed into coal...
s that flourished in equatorial
swampA swamp is a wetland featuring temporary or permanent inundation of large areas of land by shallow bodies of water. A swamp generally has a substantial number of hammocks, or dry-land protrusions, covered by aquatic vegetation, or vegetation that tolerates periodical inundation. The two main types...
s stretching from
AppalachiaAppalachia is a term used to describe a cultural region in the eastern United States that stretches from western New York state to northern Alabama, Mississippi, and Georgia. While the Appalachian Mountains stretch from Belle Isle in Canada to Cheaha Mountain in the U.S...
to
PolandPoland , officially the Republic of Poland , is a country in Central Europe . Poland is bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...
, and later on the flanks of the
UralsThe Ural Mountains are a mountain range that runs roughly north-south through western Russia. They are usually considered the natural boundary between Europe and Asia....
.
OxygenOxygen Oxygen Oxygen (acid, literally "sharp", from the taste of acids) and -γενής (-genēs) (producer, literally begetter) is the element with atomic number 8 and represented by the symbol O...
levels reached anything up to 35%, and global
carbon dioxideCarbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state...
got below the 300 parts per million level which is today associated with glacial periods. This reduction in the
greenhouse effectThe greenhouse effect is the heating of the surface of a planet or moon due to the presence of an atmosphere containing gases that absorb and emit infrared radiation. Thus, greenhouse gases trap heat within the surface-troposphere system...
was coupled with
ligninLignin or lignen is a complex chemical compound most commonly derived from wood, and an integral part of the secondary cell walls of plants and some algae. The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum, meaning wood...
and
celluloseCellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
(as tree trunks and other vegetation debris) accumulating and being buried in the great Carboniferous Coal Measures. The reduction of carbon dioxide levels in the atmosphere, would be enough to begin the process of changing polar climates, leading to cooler summers which could not melt the previous winter's snow accumulations. The growth in snowfields to 6 metres deep would create sufficient pressure to convert the lower levels to ice. Further pressure would melt the bottom layer, lubricating and letting the snowfield begin moving downslope as a
glacierA glacier is a perennial mass of ice which moves over land. A glacier forms in locations where the mass accumulation of snow and ice exceeds ablation over many years...
.
Earth's increased planetary
albedoThe albedo of an object is the extent to which it diffusely reflects light from light sources such as the Sun. It is therefore a more specific form of the term reflectivity. Albedo is defined as the ratio of diffusely reflected to incident electromagnetic radiation. It is a unitless measure...
produced by the expanding ice sheets would lead to
positive feedbackPositive feedback, sometimes referred to as "cumulative causation", refers to a situation where some effect causes more of itself. A system undergoing positive feedback is unstable, that is, it will tend to spiral out of control as the effect amplifies itself....
loops, spreading the ice sheets still further, until the process hit limit. Falling global temperatures would eventually limit plant growth, and the rising levels of oxygen would increase the frequency of fire-storms because damp plant matter could burn. Both these effects return carbon dioxide to the atmosphere, reversing the "snowball" effect and forcing greenhouse warming, with CO
2 levels rising to 300 parts per million in the following Permian period. Over a longer period the evolution of termites, whose stomachs provided an
anoxic environmentThe term anoxia means a total decrease in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts:* Anoxic waters* Anoxic event* Dead zone or hypoxic zones* Hypoxia...
for methanogenic lignin digesting bacteria, prevented further burial of carbon, returning carbon to the air as the greenhouse gas
methaneMethane is a chemical compound with the chemical formula . It is the simplest alkane, and the principal component of natural gas. Methane's bond angles are 109.5 degrees. Burning methane in the presence of oxygen produces carbon dioxide and water. The relative abundance of methane and its clean...
.
Once these factors brought a halt and a small reversal in the spread of ice sheets, the lower planetary albedo resulting from the fall in size of the glaciated areas would have been enough for warmer summers and winters and thus limit the depth of snowfields in areas from which the glaciers expanded. Rising sea levels produced by global warming drowned the large areas of flatland where previously anoxic swamps assisted in burial and removal of carbon (as
coalCoal is a readily combustible black or brownish-black sedimentary rock normally occurring in rock strata in layers or veins called coal beds. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
). With a smaller area for deposition of carbon, more carbon dioxide was returned to the atmosphere, further warming the planet. By 250 million years ago, planet Earth had returned to a percentage of oxygen similar to that found today.
The effects of the Karoo Ice Age
The rising levels of oxygen in the Karoo Ice Age had major effects upon
evolutionIn biology, evolution is change in the genetic material of a population of organisms from one generation to the next. Though changes produced in any one generation are normally small, differences accumulate with each generation and can, over time, cause substantial changes in the population, a...
of plants and animals. Higher oxygen concentration (and accompanying higher atmospheric pressure) enabled energetic metabolic processes which encouraged evolution of large land-dwelling vertebrates and flight, with the dragonfly-like
MeganeuraMeganeura monyi was a prehistoric insect of the Carboniferous period , resembling and related to the present-day dragonfly. With a wingspan of more than 75 cm wide, it was the largest known flying insect species ever to appear on Earth....
, an aerial predator, with a wingspan of 60 to 75 cm. The inoffensive stocky-bodied and armoured millipede-like
ArthropleuraArthropleura was a 0.3–2.6 metre long relative of centipedes and millipedes, native to the Upper Carboniferous of what is now northeastern North America and Scotland...
was 1.8 meters long, and the semi-terrestrial
Hibbertopterid eurypteridEurypterids are an extinct group of arthropods related to arachnids, which include the largest known arthropods that ever lived. They are members of the extinct class Eurypterida . The word Eurypterid comes from the Greek word eury meaning "broad" or "wide" and the Greek word pteron meaning...
s were perhaps as large, and some
scorpionScorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. There are about 2,000 species of scorpions, found widely distributed south of about 49° N, except New Zealand and Antarctica...
s reached 50 or 70 cm. The rising levels of oxygen also led to the evolution of greater fire resistance in vegetation and ultimately to the evolution of flowering plants. Genetic studies have shown that this was when Angiosperms separated from Cycads and Gymnosperms.
In addition, the Karoo Ice Age has unique sedimentary sequences called
cyclothemsIn geology, cyclothems are alternating stratigraphic sequences of marine and non-marine sediments, sometimes interbedded with coal seams. Unique to the Carboniferous and earliest Permian periods, they apparently formed as a result of marine transgressions and regressions related to decay and...
. These were produced by the repeated alterations of marine and nonmarine environments.
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