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Paleozoic era (541 to 245 ma)

The main events that took place during the Paleozoic were:

Life in the Paleozoic

During the Paleozoic, the diversification of invertebrate animals took place, with the first animals with shells appearing, the first crustaceans and the first corals. They stand out from them:

  • Trilobites. Arthropods with a trilobed body that became extinct at the end of the Paleozoic. They are used as guide fossils.

Trilobite Heinrich HarderBy Heinrich Harder (1858-1935) (The Wonderful Paleo Art of Heinrich Harder) [Public domain], via Wikimedia Commons

The cruzianas are fossil tracks the movement of trilobites from the bottom of the oceans.

By CorreiaPM (Own work) [Public domain], via Wikimedia Commons
  • Graptolites. Colonial planktonic animals that lived between the Cambrian and Carboniferous. Many graptolite fossils resemble written hieroglyphs, which is why they are called that. They are also used as guide fossils.

Spirograptus spiralis.jpgCC BY-SA 2.5 es,

The first vertebrates emerged, which were armored fish, with the front part of the body covered with bony plates.

Coccosteus BWDe I,, CC BY 2.5,

The animals managed to get out of the water and colonize the terrestrial environment. They appeared insects, the amphibians and reptiles.

The plants also colonized the terrestrial environment. The first vascular plants appeared, such as the giant ferns that formed forests and originated coal deposits.


De Gunnar Ries - Trabajo propio (own photo), CC BY-SA 2.5,

At the end of the Paleozoic, most of the animal and plant species disappeared. The great Permian extinction is the largest known extinction. It was caused by the increase in the greenhouse effect produced by the great volcanic activity and by the disappearance of a large part of the coasts when Pangea formed in the macrocontinent.

Cambrian (541 to 505 ma)

  • During the Cambrian Period the fragmentation of Rodinia (Pangea I) occurred. In this period, invertebrates diversify, with the first animals with shells appearing, the first crustaceans and corals.
  • The atmosphere reaches 10% O2.


millercambrian.jpg (Imagen JPEG, 500 × 367 píxeles) - Escalado (88 %). (s. f.). Recuperado a partir de

Ordovician (505 to 440 ma)

  • It began with a great extinction at the end of the Cambrian and ended with another great extinction, before the Silurian.
  • Although less famous than the Cambrian explosion, the Ordovician Period was also characterized by great adaptive radiation, especially marine fauna.
  • Trilobites, graptolites, brachiopods, bivalves, etc. abounded , all marine, since there was not much oxygen in the atmosphere. It is believed that some were able to reach the shores, but still unable to become independent from the sea.
  • The only plants that colonized the earth were non-vascular plants, such as bryophytes.
By ( [CC BY-SA 4.0], via Wikimedia Commons

Silurian (440 to 410 ma)

  • In the Silurian Period the conquest of the emerged lands begins. Vascular plants (Pteridophytes) and terrestrial arthropods manage to colonize the mainland, being able to leave the seas.
  • Due to the explosion of plant life and the conquest of the earth, the atmosphere reaches 21% O2, as it is today.
  • The first vertebrates appear, which are armored fish, with bony plates in the front area of ​​the body.
  • The Caledonian Orogeny (400-380 ma) was produced, forming mountain ranges on both sides of the present Atlantic Ocean, in ScotlandIrelandEnglandWales and western Norway.

Devonian (410 to 360 ma)

    • The first freshwater fish appeared.
    • The first amphibians arose from fish that could resist out of water. Thus the vertebrates begin their conquest of the emerged lands.
    • The first trees appeared.
    • The increased concentration of O2 in the atmosphere allowed the ozone layer to form, which protects from ultraviolet radiation from the Sun.
    • It ended with the Devonian extinction.

    Carboniferous (360 to 286 ma) 

    • Hot and humid climate that favors the development of large coniferous and fern forests that will give rise to coal deposits.
    • The first reptiles appear.
    • Development of the first amniotic membrane, which allowed animals to become independent from water.
    • Gymnosperms emerged, with specialized reproductive structures, such as seeds and pollen.
    Helechos y árboles del Parque Nacional Mount Field (Tasmania, Australia), dando una idea de cómo podría haber sido un bosque tropical carbonífero.
    By JJ Harrison ( (Own work) [GFDL 1.2 or CC BY-SA 3.0], via Wikimedia Commons

    Permian (286 to 245 ma)

    • The supercontient Pangea was formed which, together with the great volcanic activity that occurred in the Permian, significantly increased the greenhouse effect.
    • The formation of Pangea caused the Hercynian orogeny, which formed many mountain ranges.
    • The climate was hot and arid, with great thermal oscillation.
    • It ended with the great Permian extinction, the largest known extinction.
    Paisaje Pérmico con anfibios del Pérmico
    By Joseph Smit [Public domain], via Wikimedia Commons


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