Karoo Ice Age
Encyclopedia
The Karoo Ice Age from 360–260 Ma (million years ago) was the second major ice age
of the Phanerozoic
Eon
. It is named after the glacial till
s found in the Karoo
region of South Africa
where evidence for this ice age was first clearly identified.
The tectonic
assembly of the continents of Euramerica
(later with the Uralian orogeny
, into Laurasia
) and Gondwanaland into Pangaea
, in the Hercynian-Alleghany Orogeny
, made a major continental landmass within the Antarctic region, and the closure of the Rheic Ocean
and Iapetus Ocean
saw disruption of warm water currents in the Panthalassa
Ocean and Paleotethys Sea
, which led to progressive cooling of summers, and the snowfields accumulating in winters, causing mountainous alpine glacier
s to grow, and then spread out of highland areas, making continental glacier
s which spread to cover much of Gondwanaland.
At least two major periods of glaciation have been discovered:-
The extent of glaciation in Antarctica is not exactly known, due to its present ice sheet.
The shift in glacial expansion cores is due to polar wandering and tectonic movements of Pangaea.
levels. Large tree ferns, growing to 20 meters high, were secondary dominant to the large arborescent Lycopods (30-40 metres high) of the Carboniferous
coal forest
s that flourished in equatorial swamp
s stretching from Appalachia
to Poland
, and later on the flanks of the Urals
. Oxygen
levels reached anything up to 35%, and global carbon dioxide
got below the 300 parts per million level which is today associated with glacial periods. This reduction in the greenhouse effect
was coupled with lignin
and cellulose
(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 glacier
.
Earth's increased planetary albedo
produced by the expanding ice sheets would lead to positive feedback
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 CO2 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 environment
for methanogenic lignin digesting bacteria, prevented further burial of carbon, returning carbon to the air as the greenhouse gas methane
.
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 coal
). 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.
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 Meganeura
, an aerial predator, with a wingspan of 60 to 75 cm. The inoffensive stocky-bodied and armoured millipede-like Arthropleura
was 1.8 meters long, and the semi-terrestrial Hibbertopterid eurypterid
s were perhaps as large, and some scorpion
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 cyclothems
. These were produced by the repeated alterations of marine and nonmarine environments.
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...
of the Phanerozoic
Phanerozoic
The Phanerozoic Eon is the current eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 542 million years and goes back to the time when diverse hard-shelled animals first appeared...
Eon
Eon
-Science:* Aeon, a very long time* Eon , a collective problem solving project* Eon Mountain, in Canada* A measure of time in the geologic time scale- Fiction :* Eon , by Greg Bear...
. It is named after the glacial till
Till
thumb|right|Closeup of glacial till. Note that the larger grains in the till are completely surrounded by the matrix of finer material , and this characteristic, known as matrix support, is diagnostic of till....
s found in the Karoo
Karoo
The 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 Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
where evidence for this ice age was first clearly identified.
The tectonic
Tectonic Plates
Tectonic 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 Euramerica
Euramerica
Euramerica was a minor supercontinent created in the Devonian as the result of a collision between the Laurentian, Baltica, and Avalonia cratons .300 million years ago in the Late Carboniferous tropical rainforests lay over the equator of Euramerica...
(later with the Uralian orogeny
Uralian orogeny
The 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 Laurasia
Laurasia
In paleogeography, Laurasia was the northernmost of two supercontinents that formed part of the Pangaea supercontinent from approximately...
) and Gondwanaland into Pangaea
Pangaea
Pangaea, Pangæa, or Pangea is hypothesized as a supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago, before the component continents were separated into their current configuration....
, in the Hercynian-Alleghany Orogeny
Orogeny
Orogeny refers to forces and events leading to a severe structural deformation of the Earth's crust due to the engagement of tectonic plates. Response to such engagement results in the formation of long tracts of highly deformed rock called orogens or orogenic belts...
, made a major continental landmass within the Antarctic region, and the closure of the Rheic Ocean
Rheic Ocean
The 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 Ocean
Iapetus Ocean
The 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 Panthalassa
Panthalassa
Panthalassa , 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 Sea
Tethys Ocean
The 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 glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
s to grow, and then spread out of highland areas, making continental glacier
Continental Glacier
Continental 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): ice sheets expanded from a core in southern Africa and South America.
- The second glacial period was associated with the PennsylvanianPennsylvanianThe Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughly . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain...
era (318.1–299 Ma); ice sheets expanded from a core in AustraliaAustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and IndiaIndiaIndia , 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 with over 1.2 billion people, and the most populous democracy in the world...
.
The extent of glaciation in Antarctica is not exactly known, due to its present ice sheet.
The shift in glacial expansion cores is due to polar wandering and tectonic movements of Pangaea.
Causes of the Karoo Ice Age
The evolution of land plants with the onset of the Devonian period, began a long term increase in planetary oxygenOxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
levels. Large tree ferns, growing to 20 meters high, were secondary dominant to the large arborescent Lycopods (30-40 metres high) of the Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
coal forest
Coal forest
Coal forests were the vast swathes of wetlands 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 swamp
Swamp
A swamp is a wetland with some flooding of large areas of land by shallow bodies of water. A swamp generally has a large number of hammocks, or dry-land protrusions, covered by aquatic vegetation, or vegetation that tolerates periodical inundation. The two main types of swamp are "true" or swamp...
s stretching from Appalachia
Appalachia
Appalachia is a term used to describe a cultural region in the eastern United States that stretches from the Southern Tier of 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 Poland
Poland
Poland , officially the Republic of Poland , is a country in Central Europe 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 Urals
Ural Mountains
The Ural Mountains , or simply the Urals, are a mountain range that runs approximately from north to south through western Russia, from the coast of the Arctic Ocean to the Ural River and northwestern Kazakhstan. Their eastern side is usually considered the natural boundary between Europe and Asia...
. Oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
levels reached anything up to 35%, and global carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
got below the 300 parts per million level which is today associated with glacial periods. This reduction in the greenhouse effect
Greenhouse effect
The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface, energy is transferred to the surface and the lower atmosphere...
was coupled with lignin
Lignin
Lignin 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 cellulose
Cellulose
Cellulose 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
Coal Measures
The Coal Measures is a lithostratigraphical term for the coal-bearing part of the Upper Carboniferous System. It represents the remains of fluvio-deltaic sediment, and consists mainly of clastic rocks interstratified with the beds of coal...
. 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 glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
.
Earth's increased planetary albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...
produced by the expanding ice sheets would lead to positive feedback
Positive feedback
Positive feedback is a process in which the effects of a small disturbance on a system include an increase in the magnitude of the perturbation. That is, A produces more of B which in turn produces more of A. In contrast, a system that responds to a perturbation in a way that reduces its effect is...
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 CO2 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 environment
Hypoxia (medical)
Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise...
for methanogenic lignin digesting bacteria, prevented further burial of carbon, returning carbon to the air as the greenhouse gas methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
.
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 coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. 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 evolutionEvolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
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 Meganeura
Meganeura
Meganeura is a genus of extinct insects from the Carboniferous period approximately 300 million years ago, which resembled and are related to the present-day dragonflies. With wingspans of more than 75 cm , M. monyi is one of the largest known flying insect species; the Permian Meganeuropsis...
, an aerial predator, with a wingspan of 60 to 75 cm. The inoffensive stocky-bodied and armoured millipede-like Arthropleura
Arthropleura
Arthropleura 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 eurypterid
Eurypterid
Eurypterids are an extinct group of arthropods related to arachnids which include the largest known arthropods that ever lived. They are members of the extinct order Eurypterida ; which is the most diverse Paleozoic chelicerate order in terms of species...
s were perhaps as large, and some scorpion
Scorpion
Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger...
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 cyclothems
Cyclothems
In geology, cyclothems are alternating stratigraphic sequences of marine and non-marine sediments, sometimes interbedded with coal seams. Historically, the term was defined by the European coal geologists that worked in coal basins formed during the Carboniferous and earliest Permian periods...
. These were produced by the repeated alterations of marine and nonmarine environments.
Resources
- Beerling, D. J. and Berner, R. A. (2000) "Impact of a Permo-Carboniferous high O2 event on the terrestrial carbon cycle", Proc. Nat. Acad. Sci., 97 (23), p. 12428-12432
- Berner, R.A. (1999) "Atmospheric oxygen over Phanerozoic time", Proc. Nat. Acad. Sci., 96 (20), p. 10955-10957