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Cambrian

From Wikipedia, in a visual modern way
Cambrian
538.8 ± 0.2 – 485.4 ± 1.9 Ma
ক্যাম্ব্রিয়ান৫০.png
Earth in the middle of the Cambrian Period
Chronology
Etymology
Name formalityFormal
Usage information
Celestial bodyEarth
Regional usageGlobal (ICS)
Time scale(s) usedICS Time Scale
Definition
Chronological unitPeriod
Stratigraphic unitSystem
First proposed byAdam Sedgwick, 1835
Time span formalityFormal
Lower boundary definitionAppearance of the Ichnofossil Treptichnus pedum
Lower boundary GSSPFortune Head section, Newfoundland, Canada
47°04′34″N 55°49′52″W / 47.0762°N 55.8310°W / 47.0762; -55.8310
Lower GSSP ratified1992[2]
Upper boundary definitionFAD of the Conodont Iapetognathus fluctivagus.
Upper boundary GSSPGreenpoint section, Green Point, Newfoundland, Canada
49°40′58″N 57°57′55″W / 49.6829°N 57.9653°W / 49.6829; -57.9653
Upper GSSP ratified2000[3]
Atmospheric and climatic data
Sea level above present dayRising steadily from 4 m to 90 m[4]
Part of a series on
The Cambrian explosion
Cambrian explosion taskforce logo.svg
Fossil localities
Key organisms
Ediacaran biota
Burgess-type
Small shelly fauna
Evolutionary concepts
Trends
Themes
Not to be confused with Cambria or Cumbria.
For other uses, see Cambrian (disambiguation).
"Cambrian fauna" redirects here. For the first evolutionary fauna, see Evolutionary fauna § Cambrian fauna.

The Cambrian Period ( /ˈkæmbri.ən, ˈkeɪm-/ KAM-bree-ən, KAYM-; sometimes symbolized Ꞓ) is the first geological period of the Paleozoic Era, and of the Phanerozoic Eon.[5] The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago (mya) to the beginning of the Ordovician Period 485.4 mya.[6] Its subdivisions, and its base, are somewhat in flux. The period was established as "Cambrian series" by Adam Sedgwick,[5] who named it after Cambria, the Latin name for 'Cymru' (Wales), where Britain's Cambrian rocks are best exposed.[7][8][9] Sedgwick identified the layer as part of his task, along with Roderick Murchison, to subdivide the large "Transition Series", although the two geologists disagreed for a while on the appropriate categorization.[5] The Cambrian is unique in its unusually high proportion of lagerstätte sedimentary deposits, sites of exceptional preservation where "soft" parts of organisms are preserved as well as their more resistant shells. As a result, our understanding of the Cambrian biology surpasses that of some later periods.[10]

The Cambrian marked a profound change in life on Earth: prior to the Cambrian, the majority of living organisms on the whole were small, unicellular and simple (Ediacaran fauna being notable exceptions). Complex, multicellular organisms gradually became more common in the millions of years immediately preceding the Cambrian, but it was not until this period that mineralized – hence readily fossilized – organisms became common.[11] The rapid diversification of lifeforms in the Cambrian, known as the Cambrian explosion, produced the first representatives of all modern animal phyla. Phylogenetic analysis has supported the view that before the Cambrian radiation, in the Cryogenian[12][13][14] or Tonian,[15] animals (metazoans) evolved monophyletically from a single common ancestor: flagellated colonial protists similar to modern choanoflagellates.[16] Although diverse life forms prospered in the oceans, the land is thought to have been comparatively barren – with nothing more complex than a microbial soil crust[17] and a few molluscs and arthropods (albeit not terrestrial) that emerged to browse on the microbial biofilm.[18] By the end of the Cambrian, myriapods,[19][20] arachnids,[21] and hexapods[22] started adapting to the land, along with the first plants.[23][24] Most of the continents were probably dry and rocky due to a lack of vegetation. Shallow seas flanked the margins of several continents created during the breakup of the supercontinent Pannotia. The seas were relatively warm, and polar ice was absent for much of the period.

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C with bar

C with bar

The C with bar, also known as barred C, is a modified letter of the Latin alphabet, formed from C with the addition of a bar. It was used in the final version of the Unified Northern Alphabet, approved in 1932, for Saami, Selkup, Khanty, Evenki, Even, Nanai, Udege, Chukchi, Koryak and Nivkh languages to denote the sound IPA: [t͡ʃ], although in some of these languages in practice, several other alphabets were used. Also, this letter was used in the Latinized Shugnan alphabet (1931-1939) to denote the sound IPA: [t͡s].

Ediacaran

Ediacaran

The Ediacaran Period is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and the beginning of the Phanerozoic Eon. It is named after the Ediacara Hills of South Australia.

Adam Sedgwick

Adam Sedgwick

Adam Sedgwick was a British geologist and Anglican priest, one of the founders of modern geology. He proposed the Cambrian and Devonian period of the geological timescale. Based on work which he did on Welsh rock strata, he proposed the Cambrian period in 1835, in a joint publication in which Roderick Murchison also proposed the Silurian period. Later in 1840, to resolve what later became known as the Great Devonian Controversy about rocks near the boundary between the Silurian and Carboniferous periods, he and Murchison proposed the Devonian period.

Cambria

Cambria

Cambria is a name for Wales, being the Latinised form of the Welsh name for the country, Cymru. The term was not in use during the Roman or the early medieval period. After the Anglo-Saxon settlement of much of Britain, a territorial distinction developed between the new Anglo-Saxon kingdoms and the remaining Celtic British kingdoms. Latin being the primary language of scholarship in Western Christendom, medieval writers commonly used either the older term Britannia, as the territory still inhabited by Britons, or Wallia, a term derived from Old English, to refer to Wales. The term Cambria is first attested in Geoffrey of Monmouth in the 12th century as an alternative to both of these, since Britannia was now ambiguous and Wallia a foreign import, but remained rare until late in the Middle Ages.

Lagerstätte

Lagerstätte

A Lagerstätte is a sedimentary deposit that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues. These formations may have resulted from carcass burial in an anoxic environment with minimal bacteria, thus delaying the decomposition of both gross and fine biological features until long after a durable impression was created in the surrounding matrix. Lagerstätten span geological time from the Neoproterozoic era to the present. Worldwide, some of the best examples of near-perfect fossilization are the Cambrian Maotianshan shales and Burgess Shale, the Silurian Waukesha Biota, the Devonian Hunsrück Slates and Gogo Formation, the Carboniferous Mazon Creek, the Jurassic Posidonia Shale and Solnhofen Limestone, the Cretaceous Yixian, Santana, and Agua Nueva formations, the Eocene Green River Formation, the Miocene Foulden Maar and Ashfall Fossil Beds, the Pliocene Gray Fossil Site, the Pleistocene Naracoorte Caves, the La Brea Tar Pits, and the Tanis Fossil Site.

Ediacaran biota

Ediacaran biota

The Ediacaran biota is a taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period. These were composed of enigmatic tubular and frond-shaped, mostly sessile, organisms. Trace fossils of these organisms have been found worldwide, and represent the earliest known complex multicellular organisms. The term "Ediacara biota" has received criticism from some scientists due to its alleged inconsistency, arbitrary exclusion of certain fossils, and inability to be precisely defined.

Cambrian explosion

Cambrian explosion

The Cambrian explosion, Cambrian radiation, Cambrian diversification, or the Biological Big Bang refers to an interval of time approximately 538.8 million years ago in the Cambrian Period when practically all major animal phyla started appearing in the fossil record. It lasted for about 13 – 25 million years and resulted in the divergence of most modern metazoan phyla. The event was accompanied by major diversification in other groups of organisms as well.

Cryogenian

Cryogenian

The Cryogenian is a geologic period that lasted from 720 to 635 million years ago. It forms the second geologic period of the Neoproterozoic Era, preceded by the Tonian Period and followed by the Ediacaran.

Biological soil crust

Biological soil crust

Biological soil crusts are communities of living organisms on the soil surface in arid and semi-arid ecosystems. They are found throughout the world with varying species composition and cover depending on topography, soil characteristics, climate, plant community, microhabitats, and disturbance regimes. Biological soil crusts perform important ecological roles including carbon fixation, nitrogen fixation and soil stabilization; they alter soil albedo and water relations and affect germination and nutrient levels in vascular plants. They can be damaged by fire, recreational activity, grazing and other disturbances and can require long time periods to recover composition and function. Biological soil crusts are also known as biocrusts or as cryptogamic, microbiotic, microphytic, or cryptobiotic soils.

Arachnid

Arachnid

Arachnida is a class of joint-legged invertebrate animals (arthropods), in the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegaroons.

Hexapoda

Hexapoda

The subphylum Hexapoda comprises most species of arthropods and includes the insects as well as three much smaller groups of wingless arthropods: Collembola, Protura, and Diplura. The Collembola are very abundant in terrestrial environments. Hexapods are named for their most distinctive feature: a consolidated thorax with three pairs of legs. Most other arthropods have more than three pairs of legs. Most recent studies have recovered Hexapoda as a subgroup of Crustacea.

Continent

Continent

A continent is any of several large geographical regions. Continents are generally identified by convention rather than any strict criteria. A continent could be a single landmass or a part of a very large landmass, as in the case of Asia or Europe. Due to this, the number of continents varies; up to seven or as few as four geographical regions are commonly regarded as continents. Most English-speaking countries recognize seven regions as continents. In order from largest to smallest in area, these seven regions are Asia, Africa, North America, South America, Antarctica, Europe, and Australia. Different variations with fewer continents merge some of these regions, examples of this are merging North America and South America into America, Asia and Europe into Eurasia, and Africa, Asia, and Europe into Afro-Eurasia.

Stratigraphy

Further information: Stratigraphy of the Cambrian

The Cambrian Period followed the Ediacaran Period and was followed by the Ordovician Period.

The base of the Cambrian lies atop a complex assemblage of trace fossils known as the Treptichnus pedum assemblage.[25] The use of Treptichnus pedum, a reference ichnofossil to mark the lower boundary of the Cambrian, is problematic because very similar trace fossils belonging to the Treptichnids group are found well below T. pedum in Namibia, Spain and Newfoundland, and possibly in the western USA. The stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, and probably in Spain.[26][27]

Subdivisions

The Cambrian is divided into four epochs (series) and ten ages (stages). Currently only three series and six stages are named and have a GSSP (an internationally agreed-upon stratigraphic reference point).

Because the international stratigraphic subdivision is not yet complete, many local subdivisions are still widely used. In some of these subdivisions the Cambrian is divided into three epochs with locally differing names – the Early Cambrian (Caerfai or Waucoban, 538.8 ± 0.2 to 509 ± 1.9 mya), Middle Cambrian (St Davids or Albertan, 509 ± 0.2 to 497 ± 1.9 mya) and Late Cambrian (497 ± 0.2 to 485.4 ± 1.9 mya; also known as Merioneth or Croixan). Trilobite zones allow biostratigraphic correlation in the Cambrian. Rocks of these epochs are referred to as belonging to the Lower, Middle, or Upper Cambrian.

Each of the local series is divided into several stages. The Cambrian is divided into several regional faunal stages of which the Russian-Kazakhian system is most used in international parlance:

Correlation of global and regional Cambrian stratigraphy
International Series Chinese North American Russian-Kazakhian Australian Regional
C
a
m
b
r
i
a
n		 Furongian Ibexian (part) Ayusokkanian Datsonian Dolgellian (Trempealeauan, Fengshanian)
Payntonian
Sunwaptan Sakian Iverian Ffestiniogian (Franconian, Changshanian)
Steptoan Aksayan Idamean Maentwrogian (Dresbachian)
Marjuman Batyrbayan Mindyallan
Miaolingian Maozhangian Mayan Boomerangian
Zuzhuangian Delamaran Amgan Undillian
Zhungxian Florian
Templetonian
  Dyeran Ordian
Cambrian Series 2 Longwangmioan Toyonian Lenian
Changlangpuan Montezuman Botomian
Qungzusian Atdabanian
Terreneuvian
Meishuchuan
Jinningian		 Placentian Tommotian
Nemakit-Daldynian*		 Cordubian
Precambrian Sinian Hadrynian Nemakit-Daldynian*
Sakharan		 Adelaidean

*Most Russian paleontologists define the lower boundary of the Cambrian at the base of the Tommotian Stage, characterized by diversification and global distribution of organisms with mineral skeletons and the appearance of the first Archaeocyath bioherms.[28][29][30]

Dating the Cambrian

Archeocyathids from the Poleta formation in the Death Valley area
Archeocyathids from the Poleta formation in the Death Valley area

The International Commission on Stratigraphy lists the Cambrian Period as beginning at 538.8 million years ago and ending at 485.4 million years ago.

The lower boundary of the Cambrian was originally held to represent the first appearance of complex life, represented by trilobites. The recognition of small shelly fossils before the first trilobites, and Ediacara biota substantially earlier, led to calls for a more precisely defined base to the Cambrian Period.[31]

Despite the long recognition of its distinction from younger Ordovician rocks and older Precambrian rocks, it was not until 1994 that the Cambrian system/period was internationally ratified. After decades of careful consideration, a continuous sedimentary sequence at Fortune Head, Newfoundland was settled upon as a formal base of the Cambrian Period, which was to be correlated worldwide by the earliest appearance of Treptichnus pedum.[31] Discovery of this fossil a few metres below the GSSP led to the refinement of this statement, and it is the T. pedum ichnofossil assemblage that is now formally used to correlate the base of the Cambrian.[31][32]

This formal designation allowed radiometric dates to be obtained from samples across the globe that corresponded to the base of the Cambrian. Early dates of 570 million years ago quickly gained favour,[31] though the methods used to obtain this number are now considered to be unsuitable and inaccurate. A more precise date using modern radiometric dating yield a date of 538.8 ± 0.2 million years ago.[6] The ash horizon in Oman from which this date was recovered corresponds to a marked fall in the abundance of carbon-13 that correlates to equivalent excursions elsewhere in the world, and to the disappearance of distinctive Ediacaran fossils (Namacalathus, Cloudina). Nevertheless, there are arguments that the dated horizon in Oman does not correspond to the Ediacaran-Cambrian boundary, but represents a facies change from marine to evaporite-dominated strata – which would mean that dates from other sections, ranging from 544 or 542 Ma, are more suitable.[31]

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Stratigraphy of the Cambrian

Stratigraphy of the Cambrian

The Stratigraphy of the Cambrian period currently has several schemes used for ordering geologic formations from the period. The International Commission on Stratigraphy−ICS scheme has set a stratotype section for the base of the Cambrian, dated quite accurately to 538.8 ± 0.2 million years ago. Russian and Chinese scientists have developed a different scheme.

Ediacaran

Ediacaran

The Ediacaran Period is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and the beginning of the Phanerozoic Eon. It is named after the Ediacara Hills of South Australia.

Ordovician

Ordovician

The Ordovician is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period 485.4 million years ago (Mya) to the start of the Silurian Period 443.8 Mya.

Trace fossil

Trace fossil

A trace fossil, also known as an ichnofossil, is a fossil record of biological activity but not the preserved remains of the plant or animal itself. Trace fossils contrast with body fossils, which are the fossilized remains of parts of organisms' bodies, usually altered by later chemical activity or mineralization. The study of such trace fossils is ichnology and is the work of ichnologists.

Namibia

Namibia

Namibia, officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and east. Although it does not border Zimbabwe, less than 200 metres of the Botswanan right bank of the Zambezi River separates the two countries. Namibia gained independence from South Africa on 21 March 1990, following the Namibian War of Independence. Its capital and largest city is Windhoek. Namibia is a member state of the United Nations (UN), the Southern African Development Community (SADC), the African Union (AU) and the Commonwealth of Nations.

Spain

Spain

Spain, or the Kingdom of Spain, is a country primarily located in southwestern Europe with parts of territory in the Atlantic Ocean and across the Mediterranean Sea. The largest part of Spain is situated on the Iberian Peninsula; its territory also includes the Canary Islands in the Atlantic Ocean, the Balearic Islands in the Mediterranean Sea, and the autonomous cities of Ceuta and Melilla in Africa. The country's mainland is bordered to the south by Gibraltar; to the south and east by the Mediterranean Sea; to the north by France, Andorra and the Bay of Biscay; and to the west by Portugal and the Atlantic Ocean. With an area of 505,990 km2 (195,360 sq mi), Spain is the second-largest country in the European Union (EU) and, with a population exceeding 47.4 million, the fourth-most populous EU member state. Spain's capital and largest city is Madrid; other major urban areas include Barcelona, Valencia, Seville, Zaragoza, Málaga, Murcia, Palma de Mallorca, Las Palmas de Gran Canaria, and Bilbao.

Series (stratigraphy)

Series (stratigraphy)

Series are subdivisions of rock layers based on the age of the rock and formally defined by international conventions of the geological timescale. A series is therefore a sequence of strata defining a chronostratigraphic unit. Series are subdivisions of systems and are themselves divided into stages.

Stage (stratigraphy)

Stage (stratigraphy)

In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions of years of deposition. A given stage of rock and the corresponding age of time will by convention have the same name, and the same boundaries.

Global Boundary Stratotype Section and Point

Global Boundary Stratotype Section and Point

A Global Boundary Stratotype Section and Point (GSSP) is an internationally agreed upon reference point on a stratigraphic section which defines the lower boundary of a stage on the geologic time scale. The effort to define GSSPs is conducted by the International Commission on Stratigraphy, a part of the International Union of Geological Sciences. Most, but not all, GSSPs are based on paleontological changes. Hence GSSPs are usually described in terms of transitions between different faunal stages, though far more faunal stages have been described than GSSPs. The GSSP definition effort commenced in 1977. As of 2022, 78 of the 101 stages that need a GSSP have a ratified GSSP.

Trilobite zone

Trilobite zone

Trilobites are used as index fossils to subdivide the Cambrian period. Assemblages of trilobites define trilobite zones. The Olenellus-zone has traditionally marked the top of the Lower Cambrian, and is followed by the Eokochaspis zone.

Furongian

Furongian

The Furongian is the fourth and final epoch and series of the Cambrian. It lasted from 497 to 485.4 million years ago. It succeeds the Miaolingian series of the Cambrian and precedes the Lower Ordovician Tremadocian Stage. It is subdivided into three stages: the Paibian, Jiangshanian and the unnamed 10th stage of the Cambrian.

Paleogeography

Plate reconstructions suggest a global supercontinent, Pannotia, was in the process of breaking up early in the Cambrian,[33][34] with Laurentia (North America), Baltica, and Siberia having separated from the main supercontinent of Gondwana to form isolated land masses.[35] Most continental land was clustered in the Southern Hemisphere at this time, but was drifting north.[35] Large, high-velocity rotational movement of Gondwana appears to have occurred in the Early Cambrian.[36]

With a lack of sea ice – the great glaciers of the Marinoan Snowball Earth were long melted[37] – the sea level was high, which led to large areas of the continents being flooded in warm, shallow seas ideal for sea life. The sea levels fluctuated somewhat, suggesting there were "ice ages", associated with pulses of expansion and contraction of a south polar ice cap.[38]

In Baltoscandia a Lower Cambrian transgression transformed large swathes of the Sub-Cambrian peneplain into an epicontinental sea.[39]

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Plate reconstruction

Plate reconstruction

Plate reconstruction is the process of reconstructing the positions of tectonic plates relative to each other or to other reference frames, such as the earth's magnetic field or groups of hotspots, in the geological past. This helps determine the shape and make-up of ancient supercontinents and provides a basis for paleogeographic reconstructions.

Supercontinent

Supercontinent

In geology, a supercontinent is the assembly of most or all of Earth's continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", which leaves room for interpretation and is easier to apply to Precambrian times. To separate supercontinents from other groupings, a limit has been proposed in which a continent must include at least about 75% of the continental crust then in existence in order to qualify as a supercontinent.

Pannotia

Pannotia

Pannotia, also known as the Vendian supercontinent, Greater Gondwana, and the Pan-African supercontinent, was a relatively short-lived Neoproterozoic supercontinent that formed at the end of the Precambrian during the Pan-African orogeny, during the Cryogenian period and broke apart 560 Ma with the opening of the Iapetus Ocean, in the late Ediacaran and early Cambrian. Pannotia formed when Laurentia was located adjacent to the two major South American cratons, Amazonia and Río de la Plata. The opening of the Iapetus Ocean separated Laurentia from Baltica, Amazonia, and Río de la Plata. In 2022 the whole concept of Pannotia has been put into question by scientists who argue its existence is not supported by geochronology, "the supposed landmass had begun to break up well before it was fully assembled".

Laurentia

Laurentia

Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of North America, although originally it also included the cratonic areas of Greenland and also the northwestern part of Scotland, known as the Hebridean Terrane. During other times in its past, Laurentia has been part of larger continents and supercontinents and itself consists of many smaller terranes assembled on a network of Early Proterozoic orogenic belts. Small microcontinents and oceanic islands collided with and sutured onto the ever-growing Laurentia, and together formed the stable Precambrian craton seen today.

Baltica

Baltica

Baltica is a paleocontinent that formed in the Paleoproterozoic and now constitutes northwestern Eurasia, or Europe north of the Trans-European Suture Zone and west of the Ural Mountains. The thick core of Baltica, the East European Craton, is more than three billion years old and formed part of the Rodinia supercontinent at c. 1 Ga.

Siberia (continent)

Siberia (continent)

Siberia, also known as Angaraland and Angarida, is an ancient craton in the heart of Siberia. Today forming the Central Siberian Plateau, it formed an independent landmass prior to its fusion into Pangea during the Late Carboniferous-Permian. The Verkhoyansk Sea, a passive continental margin, was fringing the Siberian Craton to the east in what is now the East Siberian Lowland.

Gondwana

Gondwana

Gondwana was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic and began to break up during the Jurassic period. The final stages of break-up, involving the separation of Antarctica from South America and Australia, occurred during the Paleogene. Gondwana was not considered a supercontinent by the earliest definition, since the landmasses of Baltica, Laurentia, and Siberia were separated from it. To differentiate it from the Indian region of the same name, it is also commonly called Gondwanaland.

Snowball Earth

Snowball Earth

The Snowball Earth hypothesis proposes that, during one or more of Earth's icehouse climates, the planet's surface became entirely or nearly entirely frozen. It is believed that this occurred sometime before 650 myr during the Cryogenian period. Proponents of the hypothesis argue that it best explains sedimentary deposits that are generally believed to be of glacial origin at tropical palaeolatitudes and other enigmatic features in the geological record. Opponents of the hypothesis contest the geological evidence for global glaciation and the geophysical feasibility of an ice- or slush-covered ocean, and they emphasize the difficulty of escaping an all-frozen condition. A number of unanswered questions remain, including whether Earth was a full snowball or a "slushball" with a thin equatorial band of open water. The snowball-Earth episodes are proposed to have occurred before the sudden radiation of multicellular bioforms known as the Cambrian explosion. The most recent snowball episode may have triggered the evolution of multicellularity.

Ice cap

Ice cap

In glaciology, an ice cap is a mass of ice that covers less than 50,000 km2 (19,000 sq mi) of land area. Larger ice masses covering more than 50,000 km2 (19,000 sq mi) are termed ice sheets.

Baltoscandia

Baltoscandia

Baltoscandian Confederation or Baltoscandia is a geopolitical concept of a Baltic–Scandinavian (Nordic) union comprising Denmark, Estonia, Finland, Iceland, Latvia, Lithuania, Norway, and Sweden. The idea was proposed by a Swedish Professor Sten de Geer (1886–1933) in the journal Geografiska Annaler in 1928 and further developed by Professor Kazys Pakštas (1893–1960), a Lithuanian scientist in the field of geography and geopolitics.

Sub-Cambrian peneplain

Sub-Cambrian peneplain

The sub-Cambrian peneplain is an ancient, extremely flat, erosion surface (peneplain) that has been exhumed and exposed by erosion from under Cambrian strata over large swathes of Fennoscandia. Eastward, where this peneplain dips below Cambrian and other Lower Paleozoic cover rocks. The exposed parts of this peneplain are extraordinarily flat with relief of less than 20 m. The overlying cover rocks demonstrate that the peneplain was flooded by shallow seas during the Early Paleozoic. Being the oldest identifiable peneplain in its area the Sub-Cambrian peneplain qualifies as a primary peneplain.

Inland sea (geology)

Inland sea (geology)

An inland sea is a continental body of water which is very large in area and is either completely surrounded by dry land or connected to an ocean by a river, strait or "arm of the sea". An inland sea will generally have higher salinity than a freshwater lake, but usually lower salinity than seawater.

Climate

Glaciers likely existed during the earliest Cambrian at high and possibly even at middle palaeolatitudes,[40] possibly due to the ancient continent of Gondwana covering the South Pole and cutting off polar ocean currents. Middle Terreneuvian deposits, corresponding to the boundary between the Fortunian and Stage 2, show evidence of glaciation.[41] However, other authors believe these very early, pretrilobitic glacial deposits may not even be of Cambrian age at all but instead date back to the Neoproterozoic, an era characterised by numerous severe icehouse periods.[42] The beginning of Stage 3 was relatively cool, with the period between 521 and 517 Ma being known as the Cambrian Arthropod Radiation Cool Event (CARCE).[43] The Earth was generally very warm during Stage 4; its climate was comparable to the hot greenhouse of the Late Cretaceous and Early Palaeogene, as evidenced by a maximum in continental weathering rates over the last 900 million years and the presence of tropical, lateritic palaeosols at high palaeolatitudes during this time.[42] The Archaecyathid Extinction Warm Event (AEWE), lasting from 511 to 510.5 Ma, was particularly warm. Another warm event, the Redlichiid-Olenid Extinction Warm Event, occurred at the beginning of Stage 5.[43] It became even warmer towards the end of the period, and sea levels rose dramatically. This warming trend continued into the Early Ordovician, the start of which was characterised by an extremely hot global climate.[44]

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Gondwana

Gondwana

Gondwana was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic and began to break up during the Jurassic period. The final stages of break-up, involving the separation of Antarctica from South America and Australia, occurred during the Paleogene. Gondwana was not considered a supercontinent by the earliest definition, since the landmasses of Baltica, Laurentia, and Siberia were separated from it. To differentiate it from the Indian region of the same name, it is also commonly called Gondwanaland.

South Pole

South Pole

The South Pole, also known as the Geographic South Pole, Terrestrial South Pole or 90th Parallel South, is the southernmost point on Earth and lies antipodally on the opposite side of Earth from the North Pole, at a distance of 12,430 miles in all directions. It is one of the two points where Earth's axis of rotation intersects its surface.

Greenhouse and icehouse Earth

Greenhouse and icehouse Earth

Throughout Earth's climate history (Paleoclimate) its climate has fluctuated between two primary states: greenhouse and icehouse Earth. Both climate states last for millions of years and should not be confused with glacial and interglacial periods, which occur as alternate phases within an icehouse period and tend to last less than 1 million years. There are five known Icehouse periods in Earth's climate history, which are known as the Huronian, Cryogenian, Andean-Saharan, Late Paleozoic, and Late Cenozoic glaciations. The main factors involved in changes of the paleoclimate are believed to be the concentration of atmospheric carbon dioxide, changes in Earth's orbit, long-term changes in the solar constant, and oceanic and orogenic changes from tectonic plate dynamics. Greenhouse and icehouse periods have played key roles in the evolution of life on Earth by directly and indirectly forcing biotic adaptation and turnover at various spatial scales across time.

Ordovician

Ordovician

The Ordovician is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period 485.4 million years ago (Mya) to the start of the Silurian Period 443.8 Mya.

Flora

The Cambrian flora was little different from the Ediacaran. The principal taxa were the marine macroalgae Fuxianospira, Sinocylindra, and Marpolia. No calcareous macroalgae are known from the period.[45]

No land plant (embryophyte) fossils are known from the Cambrian. However, biofilms and microbial mats were well developed on Cambrian tidal flats and beaches 500 mya,[17] and microbes forming microbial Earth ecosystems, comparable with modern soil crust of desert regions, contributing to soil formation.[46][47] Although molecular clock estimates suggest terrestrial plants may have first emerged during the Middle or Late Cambrian, the consequent large-scale removal of the greenhouse gas CO2 from the atmosphere through sequestration did not begin until the Ordovician.[48]

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Marpolia

Marpolia

Marpolia has been interpreted as a cyanobacterium, but also resembles the modern cladophoran green algae. It is known from the Middle Cambrian Burgess shale and Early Cambrian deposits from the Czech Republic. It comprises a dense mass of entangled, twisted filaments. It may have been free-floating or grown on other objects, although there is no evidence of attachment structures. 40 specimens of Marpolia are known from the Greater Phyllopod bed, where they comprise 0.08% of the community.

Embryophyte

Embryophyte

The Embryophyta, or land plants, are the most familiar group of green plants that comprise vegetation on Earth. Embryophytes have a common ancestor with green algae, having emerged within the Phragmoplastophyta clade of green algae as sister of the Zygnematophyceae. The Embryophyta consist of the bryophytes plus the polysporangiophytes. Living embryophytes therefore include hornworts, liverworts, mosses, lycophytes, ferns, gymnosperms and flowering plants. The land plants have diplobiontic life cycles and it is accepted now that they emerged from freshwater, multi-celled algae.

Greenhouse gas

Greenhouse gas

A greenhouse gas (GHG or GhG) is a gas that absorbs and emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone (O3). Without greenhouse gases, the average temperature of Earth's surface would be about −18 °C (0 °F), rather than the present average of 15 °C (59 °F). The atmospheres of Venus, Mars and Titan also contain greenhouse gases.

Oceanic life

Main article: Cambrian explosion

The Cambrian explosion was a period of rapid multicellular growth. Most animal life during the Cambrian was aquatic. Trilobites were once assumed to be the dominant life form at that time,[49] but this has proven to be incorrect. Arthropods were by far the most dominant animals in the ocean, but trilobites were only a minor part of the total arthropod diversity. What made them so apparently abundant was their heavy armor reinforced by calcium carbonate (CaCO3), which fossilized far more easily than the fragile chitinous exoskeletons of other arthropods, leaving numerous preserved remains.[50]

The period marked a steep change in the diversity and composition of Earth's biosphere. The Ediacaran biota suffered a mass extinction at the start of the Cambrian Period, which corresponded with an increase in the abundance and complexity of burrowing behaviour. This behaviour had a profound and irreversible effect on the substrate which transformed the seabed ecosystems. Before the Cambrian, the sea floor was covered by microbial mats. By the end of the Cambrian, burrowing animals had destroyed the mats in many areas through bioturbation. As a consequence, many of those organisms that were dependent on the mats became extinct, while the other species adapted to the changed environment that now offered new ecological niches.[51] Around the same time there was a seemingly rapid appearance of representatives of all the mineralized phyla, including the Bryozoa,[52] which were once thought to have only appeared in the Lower Ordovician.[53] However, many of those phyla were represented only by stem-group forms; and since mineralized phyla generally have a benthic origin, they may not be a good proxy for (more abundant) non-mineralized phyla.[54]

A reconstruction of Margaretia dorus from the Burgess Shale, which were once believed to be green algae, but are now understood to represent hemichordates[55]
A reconstruction of Margaretia dorus from the Burgess Shale, which were once believed to be green algae, but are now understood to represent hemichordates[55]

While the early Cambrian showed such diversification that it has been named the Cambrian Explosion, this changed later in the period, when there occurred a sharp drop in biodiversity. About 515 million years ago, the number of species going extinct exceeded the number of new species appearing. Five million years later, the number of genera had dropped from an earlier peak of about 600 to just 450. Also, the speciation rate in many groups was reduced to between a fifth and a third of previous levels. 500 million years ago, oxygen levels fell dramatically in the oceans, leading to hypoxia, while the level of poisonous hydrogen sulfide simultaneously increased, causing another extinction. The later half of Cambrian was surprisingly barren and showed evidence of several rapid extinction events; the stromatolites which had been replaced by reef building sponges known as Archaeocyatha, returned once more as the archaeocyathids became extinct. This declining trend did not change until the Great Ordovician Biodiversification Event.[56][57]

Some Cambrian organisms ventured onto land, producing the trace fossils Protichnites and Climactichnites. Fossil evidence suggests that euthycarcinoids, an extinct group of arthropods, produced at least some of the Protichnites.[58] Fossils of the track-maker of Climactichnites have not been found; however, fossil trackways and resting traces suggest a large, slug-like mollusc.[59]

In contrast to later periods, the Cambrian fauna was somewhat restricted; free-floating organisms were rare, with the majority living on or close to the sea floor;[60] and mineralizing animals were rarer than in future periods, in part due to the unfavourable ocean chemistry.[60]

Many modes of preservation are unique to the Cambrian, and some preserve soft body parts, resulting in an abundance of Lagerstätten. These include Sirius Passet,[61][62] the Sinsk Algal Lens,[63] the Maotianshan Shales,[64] the Emu Bay Shale,[65] and the Burgess Shale,[66][67][68].

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Origin of water on Earth

Origin of water on Earth

The origin of water on Earth is the subject of a body of research in the fields of planetary science, astronomy, and astrobiology. Earth is unique among the rocky planets in the Solar System in having oceans of liquid water on its surface. Liquid water, which is necessary for life as we know it, continues to exist on the surface of Earth because the planet is at a distance, known as the habitable zone, far enough from the Sun that it does not lose its water, but not so far that low temperatures cause all water on the planet to freeze.

Evolution of photosynthesis

Evolution of photosynthesis

The evolution of photosynthesis refers to the origin and subsequent evolution of photosynthesis, the process by which light energy is used to assemble sugars from carbon dioxide and a hydrogen and electron source such as water. The process of photosynthesis was discovered by Jan Ingenhousz, a Dutch-born British physician and scientist, first publishing about it in 1779.

Eukaryote

Eukaryote

Eukaryota, whose members are known as eukaryotes, is a diverse domain of organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacteria and Archaea make up the other two domains.

Multicellular organism

Multicellular organism

A multicellular organism is an organism that consists of more than one cell, in contrast to unicellular organism.

Arthropod

Arthropod

Arthropods are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chitin, often mineralised with calcium carbonate. The arthropod body plan consists of segments, each with a pair of appendages. Arthropods are bilaterally symmetrical and their body possesses an external skeleton. In order to keep growing, they must go through stages of moulting, a process by which they shed their exoskeleton to reveal a new one. Some species have wings. They are an extremely diverse group, with up to 10 million species.

Mollusca

Mollusca

Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks. Around 85,000 extant species of molluscs are recognized. The number of fossil species is estimated between 60,000 and 100,000 additional species. The proportion of undescribed species is very high. Many taxa remain poorly studied.

Dinosaur

Dinosaur

Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 245 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is a subject of active research. They became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201.3 mya and their dominance continued throughout the Jurassic and Cretaceous periods. The fossil record shows that birds are feathered dinosaurs, having evolved from earlier theropods during the Late Jurassic epoch, and are the only dinosaur lineage known to have survived the Cretaceous–Paleogene extinction event approximately 66 mya. Dinosaurs can therefore be divided into avian dinosaurs—birds—and the extinct non-avian dinosaurs, which are all dinosaurs other than birds.

Mammal

Mammal

A mammal is a vertebrate animal of the class Mammalia. Mammals are characterized by the presence of milk-producing mammary glands for feeding their young, a neocortex region of the brain, fur or hair, and three middle ear bones. These characteristics distinguish them from reptiles and birds, which they diverged from in the Carboniferous Period over 300 million years ago. Around 6,400 extant species of mammals have been described and divided into 29 orders.

Bird

Bird

Birds are a group of warm-blooded vertebrates constituting the class Aves, characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight skeleton. Birds live worldwide and range in size from the 5.5 cm (2.2 in) bee hummingbird to the 2.8 m common ostrich. There are about ten thousand living species, more than half of which are passerine, or "perching" birds. Birds have wings whose development varies according to species; the only known groups without wings are the extinct moa and elephant birds. Wings, which are modified forelimbs, gave birds the ability to fly, although further evolution has led to the loss of flight in some birds, including ratites, penguins, and diverse endemic island species. The digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly seabirds and some waterbirds, have further evolved for swimming.

Hadean

Hadean

The Hadean is a geologic eon of Earth history preceding the Archean. On Earth, the Hadean coincides with the planet's formation about 4.54 billion years ago The start of the Hadean is now defined as Ma set by the age of the oldest solid material in the Solar System, found in some meteorites, about 4.567 billion years old). The Hadean ended, as defined by the International Commission on Stratigraphy (ICS), 4 billion years ago.

Archean

Archean

The Archean Eon, in older sources sometimes called the Archaeozoic, is the second of four geologic eons of Earth's history and by definition representing the time from 4 to 2.5 billion years ago. The Archean was preceded by the Hadean Eon and followed by the Proterozoic.

Age of Earth

Age of Earth

The age of Earth is estimated to be 4.54 ± 0.05 billion years (4.54 × 109 years ± 1%). This age may represent the age of Earth's accretion, or core formation, or of the material from which Earth formed. This dating is based on evidence from radiometric age-dating of meteorite material and is consistent with the radiometric ages of the oldest-known terrestrial material and lunar samples.

Symbol

The United States Federal Geographic Data Committee uses a "barred capital C" ⟨Ꞓ⟩ character to represent the Cambrian Period.[69] The Unicode character is U+A792 Ꞓ LATIN CAPITAL LETTER C WITH BAR.[70][71]

Gallery

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Stromatolite

Stromatolite

Stromatolites or stromatoliths are layered sedimentary formations (microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota. These microorganisms produce adhesive compounds that cement sand and other rocky materials to form mineral "microbial mats". In turn, these mats build up layer by layer, growing gradually over time. A stromatolite may grow to a meter or more. Although they are rare today, fossilized stromatolites provide records of ancient life on Earth.

Trilobite

Trilobite

Trilobites are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the Atdabanian stage of the Early Cambrian period and they flourished throughout the lower Paleozoic before slipping into a long decline, when, during the Devonian, all trilobite orders except the Proetida died out. The last extant trilobites finally disappeared in the mass extinction at the end of the Permian about 252 million years ago. Trilobites were among the most successful of all early animals, existing in oceans for almost 270 million years, with over 22,000 species having been described.

Anomalocaris

Anomalocaris

Anomalocaris is an extinct genus of radiodont, an order of early-diverging stem-group arthropods. The first fossils of Anomalocaris were discovered in the Ogygopsis Shale of the Stephen Formation in British Columbia, Canada by Joseph Frederick Whiteaves, with more examples found by Charles Doolittle Walcott in the Burgess Shale unit of the Stephen Formation. Other closely related fossils have been found in the older Emu Bay Shale of Australia, as well as possibly elsewhere. Originally several fossilized parts discovered separately were thought to be three separate creatures, a misapprehension corrected by Harry B. Whittington and Derek Briggs in a 1985 journal article. With a body length close to 40 centimetres, A. canadensis is thought to be one of the earliest examples of an apex predator, though others have been found in older Cambrian lagerstätten deposits.

Arthropod

Arthropod

Arthropods are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chitin, often mineralised with calcium carbonate. The arthropod body plan consists of segments, each with a pair of appendages. Arthropods are bilaterally symmetrical and their body possesses an external skeleton. In order to keep growing, they must go through stages of moulting, a process by which they shed their exoskeleton to reveal a new one. Some species have wings. They are an extremely diverse group, with up to 10 million species.

Opabinia

Opabinia

Opabinia regalis is an extinct, stem group arthropod found in the Middle Cambrian Burgess Shale Lagerstätte of British Columbia. Opabinia was a soft-bodied animal, measuring up to 7 cm in body length, and its segmented trunk had flaps along the sides and a fan-shaped tail. The head shows unusual features: five eyes, a mouth under the head and facing backwards, and a clawed proboscis that probably passed food to the mouth. Opabinia probably lived on the seafloor, using the proboscis to seek out small, soft food. Fewer than twenty good specimens have been described; 3 specimens of Opabinia are known from the Greater Phyllopod bed, where they constitute less than 0.1% of the community.

Pikaia

Pikaia

Pikaia gracilens is an extinct, primitive chordate animal known from the Middle Cambrian Burgess Shale of British Columbia. Described in 1911 by Charles Doolittle Walcott as an annelid, and in 1979 by Harry B. Whittington and Simon Conway Morris as a chordate, it became the "One of the most famous early chordate fossils," or "famously known as relative the earliest" chordates. It is estimated to have lived during the latter period of the Cambrian explosion. Since it initial discovery, more than a hundred specimens have been recovered.

Protichnites

Protichnites

Protichnites is an ichnogenus of trace fossil consisting of the imprints made by the walking activity of certain arthropods. It consists of two rows of tracks and a medial furrow between the two rows. This furrow, which may be broken, set at an angle, and of varying width and depth, is thought to be the result of the tail region contacting the substrate.

Hallucigenia

Hallucigenia

Hallucigenia is a genus of Cambrian animal resembling worms, known from articulated fossils in Burgess Shale-type deposits in Canada and China, and from isolated spines around the world. The generic name reflects the type species' unusual appearance and eccentric history of study; when it was erected as a genus, H. sparsa was reconstructed as an enigmatic animal upside down and back to front. Hallucigenia was later recognized as a lobopodian, a grade of Paleozoic panarthropods from which the velvet worms, water bears, and arthropods arose.

Lobopodia

Lobopodia

The lobopodians, members of the informal group Lobopodia, or the formally erected phylum Lobopoda Cavalier-Smith (1998), are panarthropods with stubby legs called lobopods, a term which may also be used as a common name of this group as well. While the definition of lobopodians may differ between literatures, it usually refers to a group of soft-bodied, worm-like fossil panarthropods such as Aysheaia and Hallucigenia.

Onychophora

Onychophora

Onychophora, commonly known as velvet worms or more ambiguously as peripatus, is a phylum of elongate, soft-bodied, many-legged panarthropods. In appearance they have variously been compared to worms with legs, caterpillars, and slugs. They prey upon other invertebrates, which they catch by ejecting an adhesive slime. Approximately 200 species of velvet worms have been described, although the true number of species is likely greater. The two extant families of velvet worms are Peripatidae and Peripatopsidae. They show a peculiar distribution, with the peripatids being predominantly equatorial and tropical, while the peripatopsids are all found south of the equator. It is the only phylum within Animalia that is wholly endemic to terrestrial environments, at least among extant members. Velvet worms are generally considered close relatives of the Arthropoda and Tardigrada, with which they form the proposed taxon Panarthropoda. This makes them of palaeontological interest, as they can help reconstruct the ancestral arthropod. In modern zoology they are particularly renowned for their curious mating behaviours and the bearing of live young in some species.

Cambroraster

Cambroraster

Cambroraster is an extinct monotypic genus of hurdiid radiodont, dating to the middle Cambrian, and represented by the single formally described species Cambroraster falcatus. Hundreds of specimens were found in the Burgess Shale, and described in 2019. A large animal at up to 30 cm long, it is characterized by a significantly enlarged horseshoe-shaped dorsal carapace (H-element), and presumably fed by sifting through the sediment with its well-developed tooth plates and short frontal appendages with hooked spines. It is named partially after the fictional Millennium Falcon, which its dorsal carapace resembles.

Source: "Cambrian", Wikipedia, Wikimedia Foundation, (2023, February 6th), https://en.wikipedia.org/wiki/Cambrian.

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Further Reading

Ediacaran

Silurian

Trilobite

Trace fossil

Cambrian–Ordovician extinction event

Anomalocaris

Parvancorina

Ediacaran biota

Diplichnites

Euthycarcinoidea

Wheeler Shale

Stratigraphy of the Cambrian
See also
References
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