Paleozoic

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"Primitive period" redirects here. For the use in mathematics, see Periodic function.
Paleozoic
538.8 ± 0.2 – 251.902 ± 0.024 Ma
Chronology

The Paleozoic (or Palaeozoic) Era is the earliest of three

geologic eras of the Phanerozoic
Eon. The name Paleozoic (IPA: /ˌpæli.əˈzoʊ.ɪk, -i.oʊ-, ˌpeɪ-/ pal-ee-ə-ZOH-ik, -⁠ee-oh-, pay-;[1][2]) was coined by the British geologist Adam Sedgwick in 1838[3] by combining the Greek words palaiós (παλαιός, "old") and zōḗ (ζωή), "life", meaning "ancient life"[4]).

It is the longest of the Phanerozoic eras, lasting from 538.8 to 251.902 million years ago, and is subdivided into six

geologic periods
(from oldest to youngest):

  1. Cambrian
  2. Ordovician
  3. Silurian
  4. Devonian
  5. Carboniferous
  6. Permian

The Paleozoic comes after the Neoproterozoic Era of the Proterozoic Eon and is followed by the Mesozoic Era.

The Paleozoic was a time of dramatic geological, climatic, and evolutionary change. The

conifers
) appeared.

The Paleozoic Era ended with the largest

Phanerozoic Eon,[a] the Permian–Triassic extinction event. The effects of this catastrophe were so devastating that it took life on land 30 million years into the Mesozoic Era to recover.[5]
Recovery of life in the sea may have been much faster.[6]

Geology

The beginning of the Paleozoic Era witnessed the breakup of the supercontinent of Pannotia[7][8] and ended while the supercontinent Pangaea was assembling.[9] The breakup of Pannotia began with the opening of the Iapetus Ocean and other Cambrian seas and coincided with a dramatic rise in sea level.[10]

Appalachians, Ural Mountains, and mountains of Tasmania.[9]

Periods of the Paleozoic Era

There are six periods in the Paleozoic Era: Cambrian, Ordovician, Silurian, Devonian, Carboniferous (subdivided into the Mississippian and the Pennsylvanian subperiods), and the Permian.[11]

Cambrian Period

Main article: Cambrian
Trilobites

The Cambrian spanned from 539–485 million years ago and is the first period of the Paleozoic Era of the Phanerozoic. The Cambrian marked a boom in evolution in an event known as the Cambrian explosion in which the largest number of creatures evolved in any single period of the history of the Earth. Creatures like algae evolved, but the most ubiquitous of that period were the armored arthropods, like trilobites. Almost all marine phyla evolved in this period. During this time, the supercontinent Pannotia begins to break up, most of which later became the supercontinent Gondwana.[12]

Ordovician Period

Main article: Ordovician
Cephalaspis
(a jawless fish)

The Ordovician spanned from 485–444 million years ago. The Ordovician was a time in Earth's history in which many of the

Ordovician–Silurian extinction events, in which 60% of marine invertebrates and 25% of families became extinct, and is considered the first Phanerozoic mass extinction event, and the second deadliest.[a][13]

Silurian Period

Main article: Silurian

The Silurian spanned from 444–419 million years ago. The Silurian saw the rejuvenation of life as the Earth recovered from the previous glaciation. This period saw the mass evolution of fish, as jawless fish became more numerous, jawed fish evolved, and the first freshwater fish evolved, though arthropods, such as

vascular plants (Cooksonia) allowed plants to gain a foothold on land. These early plants were the forerunners of all plant life on land. During this time, there were four continents: Gondwana (Africa, South America, Australia, Antarctica, Siberia), Laurentia (North America), Baltica (Northern Europe), and Avalonia (Western Europe). The recent rise in sea levels allowed many new species to thrive in water.[14]

Devonian Period

Main article: Devonian
Eogyrinus
(an amphibian) of the Carboniferous

The Devonian spanned from 419–359 million years ago. Also known as "The Age of the Fish", the Devonian featured a huge diversification of fish, including armored fish like

Devonian explosion when plants made lignin allowing taller growth and vascular tissue: the first trees evolved, as well as seeds. This event also diversified arthropod life, by providing them new habitats. The first amphibians also evolved, and the fish were now at the top of the food chain. Near the end of the Devonian, 70% of all species became extinct in an event known as the Late Devonian extinction, which was the Earth's second Phanerozoic mass extinction event.[a][15]

Carboniferous Period

Main article: Carboniferous

The Carboniferous spanned from 359–299 million years ago. During this time, average global temperatures were exceedingly high; the early Carboniferous averaged at about 20 degrees Celsius (but cooled to 10 °C during the Middle Carboniferous).

Carboniferous Rainforest Collapse. Gondwana was glaciated as much of it was situated around the south pole.[17]

Permian Period

Main article: Permian
Synapsid: Dimetrodon

The Permian spanned from 299–252 million years ago and was the last period of the Paleozoic Era. At the beginning of this period, all continents joined together to form the supercontinent Pangaea, which was encircled by one ocean called Panthalassa. The land mass was very dry during this time, with harsh seasons, as the climate of the interior of Pangaea was not regulated by large bodies of water. Diapsids and synapsids flourished in the new dry climate. Creatures such as Dimetrodon and Edaphosaurus ruled the new continent. The first conifers evolved, and dominated the terrestrial landscape. Near the end of the Permian, however, Pangaea grew drier. The interior was desert, and new taxa such as Scutosaurus and Gorgonopsids filled it. Eventually they disappeared, along with 95% of all life on Earth, in a cataclysm known as "The Great Dying", the third and most severe Phanerozoic mass extinction.[a][18][19]

Climate

Life in the early Paleozoic
Swamp forest in the Carboniferous

The early Cambrian climate was probably moderate at first, becoming warmer over the course of the Cambrian, as the second-greatest sustained sea level rise in the Phanerozoic got underway. However, as if to offset this trend, Gondwana moved south, so that, in Ordovician time, most of West Gondwana (Africa and South America) lay directly over the South Pole.

The early Paleozoic climate was strongly zonal, with the result that the "climate", in an abstract sense, became warmer, but the living space of most organisms of the time – the continental shelf marine environment – became steadily colder. However,

mass extinction of the Phanerozoic Eon.[a]
Over time, the warmer weather moved into the Paleozoic Era.

The

Early Palaeozoic Icehouse, culminating in the Hirnantian glaciation, 445 million years ago at the end of the Ordovician.[20]

The middle Paleozoic was a time of considerable stability. Sea levels had dropped coincident with the ice age, but slowly recovered over the course of the

metazoan life simply became hardier, or both. At any event, the far southern continental margins of Antarctica and West Gondwana became increasingly less barren. The Devonian ended with a series of turnover pulses
which killed off much of middle Paleozoic vertebrate life, without noticeably reducing species diversity overall.

There are many unanswered questions about the late Paleozoic. The

Permian extinction
.

Flora

An artist's impression of early land plants

While macroscopic plant life appeared early in the Paleozoic Era and possibly late in the Neoproterozoic Era of the earlier eon, plants mostly remained aquatic until the

Carboniferous Rainforest Collapse which fragmented this habitat, diminishing the diversity of plant life in the late Carboniferous and Permian periods.[21]

Fauna

A noteworthy feature of Paleozoic life is the sudden appearance of nearly all of the

tetrapods, 390 million years ago, and began to develop lungs. Amphibians were the dominant tetrapods until the mid-Carboniferous, when climate change greatly reduced their diversity. Later, reptiles prospered and continued to increase in number and variety by the late Permian period.[21]

See also
  • Geologic time scale – System that relates geologic strata to time
  • Precambrian – History of Earth 4600–539 million years ago
  • Cenozoic – Third era of the Phanerozoic Eon (66 million years ago to present)
  • Mesozoic – Second era of the Phanerozoic Eon: ~252–66 million years ago
  • Phanerozoic – Fourth and current eon of the geological timescale

Footnotes

  1. ^ a b c d e The list of the "big 5"
    Oxygenation Event
    .

References

  1. ^ "Paleozoic". Dictionary.com Unabridged (Online). n.d.
  2. ^ "Paleozoic". Merriam-Webster Dictionary.
  3. ^ Sedgwick, Adam (1838). "A synopsis of the English series of stratified rocks inferior to the Old Red Sandstone – with an attempt to determine the successive natural groups and formations". Proceedings of the Geological Society of London. 2 (58): 675–685, esp. p. 685.
  4. ^ "Paleozoic". Online Etymology Dictionary.
  5. ^ Sahney, S. & Benton, M.J. (2008). "Recovery from the most profound mass extinction of all time". Proceedings of the Royal Society B: Biological Sciences. 275 (1636): 759–65.
    PMID 18198148
    .
  6. ^ "Dead-ammonite bounce". Science & technology. The Economist. 5 July 2010.
  7. ^ Scotese, C.R. (2009). "Late Proterozoic plate tectonics and palaeogeography: A tale of two supercontinents, Rodinia and Pannotia". Geological Society, London, Special Publications. 326 (1): 68.
    S2CID 128845353
    . Retrieved 29 November 2015.
  8. ^ Murphy, J.B.; Nance, R.D. & Cawood, P.A. (2009). "Contrasting modes of supercontinent formation and the conundrum of Pangea". Gondwana Research. 15 (3): 408–20.
    doi:10.1016/j.gr.2008.09.005
    . Retrieved 20 December 2019.
  9. ^ a b Rogers, J.J.W. & Santosh, M. (2004). Continents and Supercontinents. Oxford, UK: Oxford University Press. p. 146.
    ISBN 978-0-19-516589-0
    .
  10. ^ Dalziel, I.W. (1997). "Neoproterozoic-Paleozoic geography and tectonics: Review, hypothesis, environmental speculation". Geological Society of America Bulletin. 109 (1): 16–42.
    doi:10.1130/0016-7606(1997)109<0016:ONPGAT>2.3.CO;2
    .
  11. ^ "The Paleozoic Era". www.ucmp.berkeley.edu. Berkeley, CA: University of California Museum of Paleontology. 2011.
  12. ^ "Cambrian". www.ucmp.berkeley.edu. Berkeley, CA: University of California Museum of Paleontology.
  13. ^ "Ordovician". www.ucmp.berkeley.edu. Berkeley, CA: University of California Museum of Paleontology.
  14. ^ "Silurian". www.ucmp.berkeley.edu. Berkeley, CA: University of California Museum of Paleontology.
  15. ^ "Devonian". www.ucmp.berkeley.edu. Berkeley, CA: University of California Museum of Paleontology.
  16. ^ Hieb, Monte. "Carboniferous Era". geocraft.com.
  17. ^ "Carboniferous". www.ucmp.berkeley.edu. Berkeley, CA: University of California Museum of Paleontology.
  18. ^ "The Great Dying". www.nhm.ac.uk. London, UK: Natural History Museum.
  19. ^ "Permian Era". www.ucmp.berkeley.edu. Berkeley, CA: University of California Museum of Paleontology.
  20. ^ Munnecke, A.; Calner, M.;
    doi:10.1016/j.palaeo.2010.08.001
    .
  21. ^ a b Sahney, S.; Benton, M.J. & Falcon-Lang, H.J. (2010). "Rainforest collapse triggered Pennsylvanian tetrapod diversification in Euramerica" (PDF abstract). Geology. 38 (12): 1079–1082.
    doi:10.1130/G31182.1
    .

Further reading



External links

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