Life expansion occured in the Paleozoic era (or Palaeozoic), a term from the Greek words palaios (παλαιός), "old" and zoe (ζωή), "life", meaning "ancient life".[1] This geologic era is the earliest and longest of the Phanerozoic Eon. Paleozoic was a time of dramatic geological and climatic changes, and biodiversity. The Cambrian period witnessed the most rapid and widespread diversification of life in Earth's history—known as the Cambrian explosion, in which most modern phyla first appeared. Fish, arthropods, amphibians, anapsids, synapsids, euryapsids and diapsids all appeared during the Paleozoic. Great forests of primitive plants covered the continents, many of which formed the coal beds of Europe and eastern North America. Towards the end of the era, large, sophisticated diapsids and synapsids were dominant, and the first modern plants (conifers) appeared. The Paleozoic Era ended with the largest extinction event in the history of Earth, the Permian–Triassic extinction event. The effects of this catastrophe was so devastating that the environment was not conducive for terrestrial life until 30 million years into the Mesozoic Era,[2] with sea-life flourishing in at least half that time.[3] Template:Expand list

Supercontinent Age (mya: millions years ago)
Gondwana ~578-96
Laurasia ~451-72
Pangaea ~336-173

Geological formationEdit

(See also: Day 3)
Supercontinents merge (358.9–298.9 million years ago)
Pangea animation 03

The supercontinent Gondwana (pronunciation: /ɡɒndˈwɑːnə/),[4] or Gondwanaland,[5] formed from the unification of several cratons in the Late Neoproterozoic. Over time, it merged with Laurussia, in the Carboniferous, to form Pangaea[fn 1].[6] Gondwana was the largest continental landmass on Earth, covering an area of 100,000,000 km2 (39,000,000 sq mi) or 64% of today's continents.[7] It was originally located in the Southern Hemisphere, incorporating several modern landmasses, that included Antarctica, South America, Africa, Madagascar, and Australia, as well as the Arabian Peninsula and the Indian subcontinent, which have now moved entirely into the Northern Hemisphere. Gondwana began to fragment in the Mesozoic.

  1. Pangaea stabilized around 335 mya.
Seed-bearing plant event (319 million years ago)
Gymnosperm life cycle (en)

Example of gymnosperm lifecycle

A whole genome duplication event in the ancestor of seed-bearing plants occurred about 319 mya.[8] This gave rise to a series of original terrestrial biodiverse seed-producing plants that replaced the lycopsid rainforests of the tropical region.[9] [10] By far the largest group of living gymnosperms are the conifers (pines, cypresses, and relatives), followed by cycads, gnetophytes (Gnetum, Ephedra and Welwitschia), and Ginkgo biloba (a single living species). Roots in some genera have fungal association with roots in the form of mycorrhiza (Pinus), while in some others (Cycas) small specialised roots called coralloid roots are associated with nitrogen-fixing cyanobacteria.

Climatic eventsEdit


As an example of the severity of the runaway greenhouse effect, Venus' oceans may have boiled away due to this phenomenon.

(See also: Day 4)
272.95 – 252 million years ago

An unknown global warming phenomena caused an abrupt climate change, suspect to have occurred since the Guadalupian age (272.95 Ma), that triggered a runaway greenhouse effect. The anomaly created a domino effect that caused the most severe anoxic conditions in Earth's oceanic history, which ultimatly led to the "The Great Dying" (Permian–Triassic extinction event) in 252 Ma.

The domino effect can be explained by the Clathrate gun hypothesis. It proposes that increases in sea temperatures (and/or drops in sea levels) can trigger a catastrophic positive feedback effect on climate: first, warming causes a sudden release of methane from methane clathrate compounds buried in seabeds and seabed permafrost; second, because methane itself is a powerful greenhouse gas, temperatures rise further, and the cycle repeats. This runaway process, once started, could be as irreversible as the firing of a gun.[11]

Permian decline from 272.95 Ma

P-T was Earth's most severe known extinction event, with up to 96% of all marine species[12][13] and 70% of terrestrial species becoming extinct.[2] It is the only known mass extinction of insects.[14][15] Some 57% of all families and 83% of all genera became extinct. Because so much biodiversity was lost, the recovery of life on Earth took significantly longer than after any other extinction event,[12] possibly up to 10 million years.[16] Studies in Bear Lake County near Paris, Idaho showed a quick and dynamic rebound in a marine ecosystem, illustrating the remarkable resiliency of life.[17]

Notable article on subject
290px-NASA logo.svg
The Great Dying, NASA, Jan 28, 2002


(See also: Day 5)

After the Permian–Triassic extinction event, the Mesozoic Era beings. This period spans from about 252 to 66 million years ago. Paleontologists call this period the Age of Reptiles in view of the Earth being dominated by diapsids such as Iguanodon, Megalosaurus, Plesiosaurus and Pterodactylus. The paleobotanist calls it the Age of Conifers.[18]

Great sea and land creatures (250–231.4 million years ago)

See also: Fish

About 10 million years after the Permian–Triassic extinction event, the "Great Dying" (252 mya), an explosion of a variety of fish, in the class of Teleost, appeared in the Early Triassic period. Additionally, after the quick and dynamic rebound of marine ecosystems,[19] a diverse group of reptiles[20] of the clade Dinosauria, appeared between 243 and 231 million years ago,[21] The exact origin and timing of Dinosauria appearance is the subject of active research in academia.[22] They became the dominant terrestrial vertebrates after the Triassic–Jurassic extinction event 201 million years ago; their dominance continued through the Jurassic and Cretaceous periods. In the mid-Jurassic period, around 170 million years ago, the appearance of bird-like dinosaurs (which lie outside class Aves proper), existed the Archaeopteryx. These were not capable of fully powered flight, many had toothy jaws and long bony tails, thus are classed in the broader group Avialae.[23]

Notes for further research
  • Pangea breaks apart, 175 mya
Flying creatures (120 million years ago)

True birds first appeared during the Cretaceous period, around 120 million years ago.[24] DNA-based evidence finds that birds diversified dramatically around the time of the Cretaceous–Palaeogene extinction event 66 million years ago, which killed off the pterosaurs and all the non-avian dinosaur lineages. Birds, especially those in the southern continents, survived this event and then migrated to other parts of the world while diversifying during periods of global cooling.[25]

End of Cretaceous period (66 million years ago)


  1. "Paleozoic". Online Etymology Dictionary. 
  2. 2.0 2.1 Sahney, S.; Benton, M.J. (2008). "Recovery from the most profound mass extinction of all time" (PDF). Proceedings of the Royal Society: Biological 275 (1636): 759–65. doi:10.1098/rspb.2007.1370. PMID 18198148. PMC: 2596898. 
  3. The Economist
  4. "Gondwana". Lexico Publishing Group. 
  5. "Gondwanaland". Merriam-Webster Online Dictionary. 
  6. Rogers, J.J.W.; Santosh, M. (2004), Continents and Supercontinents, Oxford: Oxford University Press, p. 146, ISBN 0-19-516589-6 
  7. Torsvik & Cocks 2013, Abstract
  8. Jiao Y, Wickett NJ, Ayyampalayam S, Chanderbali AS, Landherr L, Ralph PE, Tomsho LP, Hu Y, Liang H, Soltis PS, Soltis DE, Clifton SW, Schlarbaum SE, Schuster SC, Ma H, Leebens-Mack J, Depamphilis CW (2011) Ancestral polyploidy in seed plants and angiosperms. Nature
  9. Sahney, S.; Benton, M.J.; Falcon-Lang, H.J. (2010). "Rainforest collapse triggered Pennsylvanian tetrapod diversification in Euramerica" (PDF). Geology 38 (12): 1079–1082. doi:10.1130/G31182.1. Bibcode2010Geo....38.1079S. 
  10. Campbell and Reece; Biology, Eighth edition
  11. Kennett, James P.; Cannariato, Kevin G.; Hendy, Ingrid L.; Behl, Richard J. (2003). Methane Hydrates in Quaternary Climate Change: The Clathrate Gun Hypothesis. Washington DC: American Geophysical Union. ISBN 0-87590-296-0. 
  12. 12.0 12.1 Benton M J (2005). When life nearly died: the greatest mass extinction of all time. London: Thames & Hudson. ISBN 0-500-28573-X. 
  13. Carl T. Bergstrom; Lee Alan Dugatkin (2012). Evolution. Norton. p. 515. ISBN 978-0-393-92592-0. 
  14. "Insect diversity in the fossil record". Science 261 (5119): 310–315. 1993. doi:10.1126/science.11536548. PMID 11536548. Bibcode1993Sci...261..310L. 
  15. "Extinctions and Biodiversity in the Fossil Record". Encyclopedia of Global Environmental Change, The Earth System – Biological and Ecological Dimensions of Global Environmental Change (Volume 2). New York: Wiley. 2003. pp. 297–391. ISBN 0-470-85361-1. 
  16. "It Took Earth Ten Million Years to Recover from Greatest Mass Extinction". ScienceDaily. 27 May 2012. Retrieved on 28 May 2012. 
  17. "Fossils show quick rebound of life after ancient mass extinction". Reuters. 2017-02-15. 
  18. Dean, Dennis R. (1999). Gideon Mantell and the Discovery of Dinosaurs. Cambridge University Press. pp. 97–98. ISBN 0521420482. 
  19. "Fossils show quick rebound of life after ancient mass extinction". Reuters. 2017-02-15. 
  20. Although dinosaurs are reptiles, views on them as being cold-blooded animals have changed in recent years; see physiology for more details.
  21. Alcobar, Oscar A.; Martinez, Ricardo N. (19 October 2010). "A new herrerasaurid (Dinosauria, Saurischia) from the Upper Triassic Ischigualasto Formation of northwestern Argentina". ZooKeys 63 (63): 55–81. doi:10.3897/zookeys.63.550. PMID 21594020. 
  22. Nesbitt, Sterling J.; Barrett, Paul M.; Werning, Sarah; Sidor, Christian A.; Charig, Alan J. (5 December 2012). "The oldest dinosaur? A Middle Triassic dinosauriform from Tanzania". Biology Letters 9 (1): 20120949. doi:10.1098/rsbl.2012.0949. PMID 23221875. PMC: 3565515. 
  23. Xu, X; You, H; Du, K; Han, F (28 July 2011). "An Archaeopteryx-like theropod from China and the origin of Avialae". Nature 475 (7357): 465–470. doi:10.1038/nature10288. PMID 21796204. 
  24. Brown, J.W.; Van Tuinen, M. (2011). "Evolving Perceptions on the Antiquity of the Modern Avian Tree, in Living Dinosaurs". The Evolutionary History of Modern Birds (John Wiley & Sons LtD): 306–324. doi:10.1002/9781119990475.ch12. ISBN 9781119990475. 
  25. "Influence of Earth's history on the dawn of modern birds". American Museum of Natural History. December 11, 2015.