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The Cambrian Period ( ; sometimes symbolized ) was the first
geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of divisions into which geologist A geologist is a s ...
of the
Paleozoic The Paleozoic (or Palaeozoic) Era ( ; from the Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its popula ...
Era, and of the
Phanerozoic Eon The Phanerozoic Eon is the current geologic eon in the geologic time scale The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontolo ...
. The Cambrian lasted 55.6 million years from the end of the preceding
Ediacaran The Ediacaran Period ( ) is a geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of ...
Period 541 million years ago (mya) to the beginning of the
Ordovician The Ordovician ( ) is a geologic period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of divisions i ...

Ordovician
Period mya. Its subdivisions, and its base, are somewhat in flux. The period was established as "Cambrian series" by
Adam Sedgwick Adam Sedgwick (; 22 March 1785 – 27 January 1873) was a British geologist A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shap ...

Adam Sedgwick
, who named it after
Cambria Cambria is a name for Wales, being the Latinised form of the Welsh language, Welsh name for the country, . The term was not in use during the Roman Britain, Roman period (when Wales had not come into existence as a distinct entity). It emerged lat ...

Cambria
, the Latin name for 'Cymru' (
Wales Wales ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, and the Bristol Channel to the south. It ...

Wales
), where Britain's Cambrian rocks are best exposed. The Cambrian is unique in its unusually high proportion of 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. The Cambrian marked a profound change in ; prior to the Cambrian, the majority of living organisms on the whole were small,
unicellular A unicellular organism, also known as a single-celled organism, is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Or ...
and simple; the
Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic The Phanerozoic Eon is the current geologic eon in the geologic time scale The geologi ...

Precambrian
''
Charnia ''Charnia'' is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a ...

Charnia
'' being exceptional. Complex,
multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxonomy (biol ...
s 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. The rapid diversification of life forms in the Cambrian, known as the Cambrian explosion, produced the first representatives of all modern animal phyla.
Phylogenetic analysis In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms, ...

Phylogenetic analysis
has supported the view that during the Cambrian radiation,
metazoa Animals (also called Metazoa) are multicellular Multicellular organisms are organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the L ...
(
animals Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells ...

animals
) evolved monophyletically from a single common ancestor: flagellated colonial
protists A protist () is any eukaryotic organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology, properties of life. It is a synonym f ...
similar to modern
choanoflagellates The choanoflagellates are a group of free-living unicellular and colonial flagellate 's '' Artforms of Nature'', 1904 (''Giardia lamblia'') ('' Chlamydomonas'') A flagellate is a cell or organism with one or more whip-like Appendage, appendage ...
. 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 crustSoil crusts are soil Soil (often stylized as SOiL) is an American rock band that was formed in Chicago (''City in a Garden''); I Will , image_map = , map_caption = Interactive maps of Chicago , coordinates ...

soil crust
and a few molluscs that emerged to browse on the microbial biofilm. Most of the
continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of th ...

continent
s 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 In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is composed, and the proces ...
Pannotia Pannotia (from Greek: ''pan- Pan may refer to: Prefix *''Pan-'', a prefix from the Greek language, Greek πᾶν, ''pan'', meaning "all", "of everything", or "involving all members" of a group ** , most but not all using the prefix People * Pan ...

Pannotia
. The seas were relatively warm, and polar ice was absent for much of the period.


Stratigraphy

The base of the Cambrian lies atop a complex assemblage of
trace fossil A trace fossil, also ichnofossil (; from el, ἴχνος ''ikhnos'' "trace, track"), is a fossil A fossil (from Classical Latin Classical Latin is the form of Latin language Latin (, or , ) is a classical language belonging to ...
s known as the ''
Treptichnus pedum ''Treptichnus'' (formerly named ''Phycodes pedum'', ''Manykodes pedum'' by Jerzy Dzik, J. Dzik, and also known as ''Trichophycus pedum'') is the preserved burrow of an animal. As such, it is regarded as the earliest widespread complex trace fossi ...

Treptichnus pedum
'' assemblage.A. Knoll, M. Walter, G. Narbonne, and N. Christie-Blick (2004)
The Ediacaran Period: A New Addition to the Geologic Time Scale.
Submitted on Behalf of the Terminal Proterozoic Subcommission of the International Commission on Stratigraphy.
The use of ''Treptichnus pedum'', a reference
ichnofossil '' footprints in a Triassic sandstone '' from the Cambrian, Blackberry Hill, central Wisconsin Wisconsin () is a state in the Upper Midwest region of the United States The United States of America (USA), commonly known as the ...
to mark the lower boundary of the Cambrian, is difficult since the occurrence of very similar trace fossils belonging to the Treptichnids group are found well below the ''T. pedum'' in
Namibia Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa Southern Africa is the south South is one of the cardinal directions or compass points. South is the opposite of north and is perpendicular to the east a ...

Namibia
,
Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = , national_anthem = , image_map = , map_caption = , image_map2 ...

Spain
and
Newfoundland Newfoundland and Labrador (, ) is the easternmost provinces and territories of Canada, province of Canada, in the country's Atlantic Canada, Atlantic region. It is composed of the island of Newfoundland (island), Newfoundland and the continental ...

Newfoundland
, and possibly in the western USA. The stratigraphic range of ''T. pedum'' overlaps the range of the
Ediacaran The Ediacaran Period ( ) is a geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of ...
fossils in Namibia, and probably in Spain.M.A. Fedonkin, B.S. Sokolov, M.A. Semikhatov, N.M.Chumakov (2007).
Vendian versus Ediacaran: priorities, contents, prospectives.
" In: edited by M. A. Semikhatov
The Rise and Fall of the Vendian (Ediacaran) Biota. Origin of the Modern Biosphere. Transactions of the International Conference on the IGCP Project 493, August 20–31, 2007, Moscow.
" Moscow: GEOS.
A. Ragozina, D. Dorjnamjaa, A. Krayushkin, E. Serezhnikova (2008).

. 33 Intern. Geol. Congr. 6–14 August 2008, Oslo, Norway. Abstracts. Section HPF 07 Rise and fall of the Ediacaran (Vendian) biota. p. 183.


Subdivisions

The Cambrian Period followed the
Ediacaran The Ediacaran Period ( ) is a geological period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of ...
Period and was followed by the
Ordovician The Ordovician ( ) is a geologic period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of divisions i ...

Ordovician
Period. The Cambrian is divided into four epochs (
series Series may refer to: People with the name * Caroline Series (born 1951), English mathematician, daughter of George Series * George Series (1920–1995), English physicist Arts, entertainment, and media Music * Series, the ordered sets used i ...
) and ten ages (
stages Stage or stages may refer to: Acting * Stage (theatre) In theatre and performing arts, the stage (sometimes referred to as the deck in stagecraft) is a designated space for the performance of theatrical production, productions. The stage s ...
). Currently only three series and six stages are named and have a
GSSP The 'golden spike' marking the Ediacaran GSSP A Global Boundary Stratotype Section and Point (GSSP) is an internationally agreed upon reference point on a stratigraphic through Jurassic The Jurassic ( ) is a Geological period, geologic period a ...
(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 series (epochs) with locally differing names – the Early Cambrian (Caerfai or Waucoban, mya),
Middle Cambrian Middle or The Middle may refer to: * Centre (geometry) In geometry, a centre (or center) (from Ancient Greek language, Greek ''κέντρον'') of an object is a point in some sense in the middle of the object. According to the specific definit ...
(St Davids or Albertan, mya) and
Furongian The Furongian is the fourth and final epoch and series of the Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 55.6 mi ...
( mya; also known as Late Cambrian, 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: *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 bioherms.


Dating the Cambrian

The International Commission on Stratigraphy list the Cambrian period as beginning at and ending at . The lower boundary of the Cambrian was originally held to represent the first appearance of complex life, represented by
trilobite Trilobites (; meaning "three lobes") are a group of marine s that form the 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 of the ( ...

trilobite
s. The recognition of small shelly fossils before the first trilobites, and
Ediacara biota The Ediacaran (; formerly Vendian) biota is a Taxonomy (biology), taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period (c. 635–541 Year#mya, Mya). These were composed of enig ...
substantially earlier, led to calls for a more precisely defined base to the Cambrian period. Despite the long recognition of its distinction from younger
Ordovician The Ordovician ( ) is a geologic period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of divisions i ...

Ordovician
rocks and older
Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic The Phanerozoic Eon is the current geologic eon in the geologic time scale The geologi ...

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 Newfoundland and Labrador (, ) is the easternmost provinces and territories of Canada, province of Canada, in the country's Atlantic Canada, Atlantic region. It is composed of the island of Newfoundland (island), Newfoundland and the continental ...

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 ''Treptichnus'' (formerly named ''Phycodes pedum'', ''Manykodes pedum'' by Jerzy Dzik, J. Dzik, and also known as ''Trichophycus pedum'') is the preserved burrow of an animal. As such, it is regarded as the earliest widespread complex trace fossi ...

Treptichnus pedum
''. 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. 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 quickly gained favour, 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 . The ash horizon in Oman from which this date was recovered corresponds to a marked fall in the abundance of
carbon-13 Carbon-13 (13C) is a natural, stable isotope The term stable isotope has a meaning similar to stable nuclide Stable nuclides are nuclide A nuclide (or nucleide, from nucleus, also known as nuclear species) is a class of atoms characterized by ...

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.


Paleogeography

Plate reconstructions suggest a global supercontinent,
Pannotia Pannotia (from Greek: ''pan- Pan may refer to: Prefix *''Pan-'', a prefix from the Greek language, Greek πᾶν, ''pan'', meaning "all", "of everything", or "involving all members" of a group ** , most but not all using the prefix People * Pan ...

Pannotia
, was in the process of breaking up early in the period, with
Laurentia Image:North america craton nps.gif, upright=1.4, Laurentia, also called the North American craton Laurentia or the North American Craton is a large continental craton that forms the Geology of North America, ancient geological core of North Ameri ...
(North America),
Baltica Baltica is a paleocontinent A paleocontinent or palaeocontinent is a distinct area of continental crust 350px, The thickness of Crust (geology)#Earth's crust, Earth's crust (km) Continental crust is the layer of Igneous rock, igneous, Sedim ...
, and
Siberia Siberia (; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a part of R ...
having separated from the main supercontinent of
Gondwana Gondwana () or Gondwanaland was a supercontinent In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (ge ...

Gondwana
to form isolated land masses. Most continental land was clustered in the Southern Hemisphere at this time, but was drifting north. Large, high-velocity rotational movement of Gondwana appears to have occurred in the Early Cambrian. With a lack of sea ice – the great glaciers of the Marinoan
Snowball Earth The Snowball Earth hypothesis proposes that, during one or more of Earth's Greenhouse and icehouse Earth, icehouse climates, the Earth's surface, planet's surface became entirely or nearly entirely frozen. It is believed that this occurred someti ...
were long melted – 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 In glaciology Lateral moraine on a glacier joining the Gorner Glacier, Zermatt">Gorner_Glacier.html" ;"title="moraine on a glacier joining the Gorner Glacier">moraine on a glacier joining the Gorner Glacier, Zermatt, Swiss Alps. The moraine is ...
. In
Baltoscandia Location of the Nordic countries and of the Baltic states: ">Baltic_states.html" ;"title="Nordic countries and of the Baltic states">Nordic countries and of the Baltic states: The Baltoscandian Confederation or Baltoscandia is a geopolitica ...
a Lower Cambrian transgression transformed large swathes of the
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 ...
into an epicontinental sea.


Climate

The Earth was generally cold during the early Cambrian, probably due to the ancient continent of Gondwana covering the
South Pole The South Pole, also known as the Geographic South Pole, Terrestrial South Pole or 90th Parallel South, is one of the where intersects its surface. It is the southernmost point on Earth and lies on the of Earth from the . Situated on the ...
and cutting off polar ocean currents. However, average temperatures were 7 degrees Celsius higher than today. There were likely polar ice caps and a series of glaciations, as the planet was still recovering from an earlier
Snowball Earth The Snowball Earth hypothesis proposes that, during one or more of Earth's Greenhouse and icehouse Earth, icehouse climates, the Earth's surface, planet's surface became entirely or nearly entirely frozen. It is believed that this occurred someti ...
. It became warmer towards the end of the period; the glaciers receded and eventually disappeared, and sea levels rose dramatically. This trend would continue into the
Ordovician The Ordovician ( ) is a geologic period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of divisions i ...

Ordovician
period.


Flora

The Cambrian flora was little different from the Ediacaran. The principle taxa were the marine macroalgae '' Fuxianospira'', '' Sinocylindra'', and '' Marpolia''. No calcareous macroalgae are known from the period. No
land plant The Embryophyta (), or land plants, are the most familiar group of green plant Plants are predominantly photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things that w ...
(
embryophyte The Embryophyta (), or land plants, are the most familiar group of green plant Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into ...

embryophyte
) fossils are known from the Cambrian. However, biofilms and microbial mats were well developed on Cambrian tidal flats and beaches 500 mya., and microbes forming microbial Earth ecosystems, comparable with modern
soil crustSoil crusts are soil Soil (often stylized as SOiL) is an American rock band that was formed in Chicago (''City in a Garden''); I Will , image_map = , map_caption = Interactive maps of Chicago , coordinates ...

soil crust
of desert regions, contributing to soil formation.


Oceanic life

Most animal life during the Cambrian was aquatic.
Trilobite Trilobites (; meaning "three lobes") are a group of marine s that form the 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 of the ( ...

Trilobite
s were once assumed to be the dominant life form at that time, but this has proven to be incorrect.
Arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Euarthropoda,Reference showing that Euarthropoda is a phylum: ...
s 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
chitin Chitin (carbon, C8hydrogen, H13oxygen, O5nitrogen, N)n ( ) is a long-chain polymer of N-Acetylglucosamine, ''N''-acetylglucosamine, an amide derivative of glucose. The second most abundant polysaccharide in nature (behind only cellulose), it ...

chitin
ous exoskeletons of other arthropods, leaving numerous preserved remains. The period marked a steep change in the diversity and composition of Earth's biosphere. The
Ediacaran biota The Ediacaran (; formerly Vendian) biota is a Taxonomy (biology), taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period (c. 635–541 Year#mya, Mya). These were composed of enig ...
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 The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as 'seabeds'. The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...

seabed
ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...

ecosystem
s. Before the Cambrian, the sea floor was covered by
microbial mat The cyanobacterial algal mat, salty lake on the White Sea">algal_mat.html" ;"title="cyanobacterial algal mat">cyanobacterial algal mat, salty lake on the White Sea seaside A microbial mat is a multi-layered sheet of microorganisms, mainly bacteria ...
s. By the end of the Cambrian, burrowing animals had destroyed the mats in many areas through
bioturbation Bioturbation is defined as the reworking of soil Surface-water- gley developed in glacial till, Northern Ireland.">Northern_Ireland.html" ;"title="glacial till, Northern Ireland">glacial till, Northern Ireland. Soil is a mixture of organic m ...
. 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. Around the same time there was a seemingly rapid appearance of representatives of all the mineralized phyla except the
Bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the ...

Bryozoa
, which appeared in the Lower
Ordovician The Ordovician ( ) is a geologic period A geological period is one of the several subdivisions of geologic time enabling cross-referencing of rocks and geologic events from place to place. These periods form elements of a hierarchy of divisions i ...

Ordovician
. 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. 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 Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within ...

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 Hydrogen sulfide is a chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by havi ...

hydrogen sulfide
simultaneously increased, causing another extinction. The later half of Cambrian was surprisingly barren and showed evidence of several rapid extinction events; the
stromatolite Stromatolites () or stromatoliths (from Greek "layer, stratum" ( GEN ), and "rock") are layered sedimentary Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at the Ea ...

stromatolite
s which had been replaced by reef building sponges known as
Archaeocyatha Archaeocyatha (or archaeocyathids “ancient cups” ) is a taxon of extinct, Sessility (zoology), sessile, reef-building Marine (ocean), marine organisms of warm tropical and subtropical waters that lived during the early (lower) Cambrian Period ...

Archaeocyatha
, returned once more as the archaeocyathids became extinct. This declining trend did not change until the
Great Ordovician Biodiversification Event The Ordovician radiation, or the Great Ordovician Biodiversification Event (GOBE), was an evolutionary radiation of animal life throughout the Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six perio ...
. Some Cambrian organisms ventured onto land, producing the trace fossils ''
Protichnites ''Protichnites'' is an ichnogenus An ichnotaxon (plural ichnotaxa) is "a taxon In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processe ...

Protichnites
'' and ''
Climactichnites ''Climactichnites'' is an enigmatic, Cambrian fossil formed on or within sandy tidal flats around . It has been interpreted in many different ways in the past, but is now thought to be a trace fossil '' footprints in a Triassic sandstone '' fro ...
''. Fossil evidence suggests that euthycarcinoids, an extinct group of arthropods, produced at least some of the ''Protichnites''. Fossils of the track-maker of ''Climactichnites'' have not been found; however, fossil trackways and resting traces suggest a large,
slug Slug, or land slug, is a common name Common may refer to: Places * Common, a townland in County Tyrone, Northern Ireland * Boston Common Boston Common (also known as the Common) is a central public park in downtown Boston, Massachusetts. ...

slug
-like
mollusc Mollusca is the second-largest phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of number ...
. 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; and mineralizing animals were rarer than in future periods, in part due to the unfavourable
ocean chemistry Ocean chemistry, also known as marine chemistry, is influenced by plate tectonics File:Earth cutaway schematic-en.svg, upright=1.35, Diagram of the internal layering of Earth showing the lithosphere above the asthenosphere (not to scale) Pla ...
. Many modes of preservation are unique to the Cambrian, and some preserve soft body parts, resulting in an abundance of .


Symbol

The United States
Federal Geographic Data Committee The Federal Geographic Data Committee (FGDC) is a United States government committee which promotes the coordinated development, use, sharing, and dissemination of geospatial data on a national basis. Its 32 members are representatives from the Ex ...
uses a "barred capital C" character to represent the Cambrian Period. The
Unicode Unicode, formally the Unicode Standard, is an information technology Technical standard, standard for the consistent character encoding, encoding, representation, and handling of Character (computing), text expressed in most of the world's wri ...

Unicode
character is .Unicode Character 'LATIN CAPITAL LETTER C WITH BAR' (U+A792)
fileformat.info. Retrieved 15 June 2015


Gallery

File:CambrianStromatolites.jpg,
Stromatolite Stromatolites () or stromatoliths (from Greek "layer, stratum" ( GEN ), and "rock") are layered sedimentary Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at the Ea ...

Stromatolite
s of the Pika Formation (Middle Cambrian) near Helen Lake, Banff National Park, Canada File:Elrathia kingii growth series.jpg,
Trilobite Trilobites (; meaning "three lobes") are a group of marine s that form the 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 of the ( ...

Trilobite
s were very common during this time File:Anomalocaris BW.jpg, ''
Anomalocaris ''Anomalocaris'' ("unlike other shrimp", or "abnormal shrimp") is an extinct genus of radiodont Radiodonta is an Order (biology), order of stem-group arthropods that was successful worldwide during the Cambrian period, and included the earliest l ...

Anomalocaris
'' was an early marine predator, among the various
arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Euarthropoda,Reference showing that Euarthropoda is a phylum: ...
s of the time. File:Pikaia BW.jpg, ''
Pikaia ''Pikaia gracilens'' is an extinct, primitive chordate A chordate () is an animal of the phylum Chordata (). All chordates possess 5 Apomorphy and synapomorphy , synapomorphies, or primary characteristics, at some point during their larval ...
'' was an early chordate from the Middle Cambrian File:Opabinia BW2.jpg, ''
Opabinia ''Opabinia regalis'' is an extinct Extinction is the termination of a kind of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the L ...

Opabinia
'' was a creature with an unusual body plan; it was probably related to arthropods File:Protichnites, Blackberry Hill, Wisconsin, Cambrian 2.jpg, ''
Protichnites ''Protichnites'' is an ichnogenus An ichnotaxon (plural ichnotaxa) is "a taxon In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processe ...

Protichnites
'' were the trackways of arthropods that walked Cambrian beaches File:Hallucigenia reconstructions.jpg, ''
Hallucigenia ''Hallucigenia'' is a genus of Cambrian animal known from articulated fossils in Burgess Shale-type preservation, Burgess Shale-type deposits in Canada and China, and from isolated spines around the world. The generic name reflects the type spe ...

Hallucigenia
'' may have been an early ancestor of the . Reconstructions of H. sparsa, H. hongmeia, and H. fortis File:Burgess scale2.png, Size comparison of different Cambrian species File:20200329 Cambroraster falcatus.png, falcatus was a large arthropod for the era


See also

* Cambro-Ordovician extinction event – circa 488 mya *
Dresbachian The Dresbachian is a Maentwrogian regional stage of North America, lasting from 501 to 497 million years ago.https://engineering.purdue.edu/Stratigraphy/resources/geowhen/stages/Maentwrogian.html It is part of the Upper Cambrian and is defined by fo ...
extinction event—circa 499 mya * End Botomian extinction event—circa 513 mya *
List of fossil sites This list of fossil sites is a worldwide list of localities known well for the presence of fossils A fossil (from Classical Latin Classical Latin is the form of Latin language Latin (, or , ) is a classical language belonging to th ...
''(with link directory)'' *
Type locality (geology) Type locality, also called type area, is the Wikt:locality, locality where a particular Rock (geology), rock type, Lithostratigraphy#Types of lithostratigraphic units, stratigraphic unit or Mineral, mineral species is first identified. If the str ...
, the locality where a particular rock type, stratigraphic unit, fossil or mineral species is first identified


References


Further reading

* * * * * * * * * *


External links

*
Biostratigraphy
– includes information on Cambrian trilobite
biostratigraphy Biostratigraphy is the branch of stratigraphy Stratigraphy is a branch of geology concerned with the study of rock (geology), rock layers (Stratum, strata) and layering (stratification). It is primarily used in the study of sedimentary rock, sed ...

Dr. Sam Gon's trilobite pages
(contains numerous Cambrian trilobites)


Paleomap Project

Report on the web on Amthor and others from ''Geology'' vol. 31




{{Authority control Geological periods