Cambrian Period

What happened during this time?

Geophysical

• The Period begins with carbon dioxide levels ~4,200 ppm, which jumps to 6,000 ppm in mid-Cambrian, and ending with 5,000 ppm

• Oxygen levels are relatively stable during this time at 16.5%

• Most of Cambrian life evolved and lived solely in the shallow seas that were formed as the supercontinent Pannotia split apart.

• Limited soils during this time, but some evidence of paleosols (Retallack 2013; Retallack & Broz 2020)

  • Probable bacterial/algal crusts were present on the landscape, especially in near water environments

Biological

Flora

• Autotrophic bacteria flourishing in oceans

  • Stromatolites almost completely disappear

• Algae dominant in oceans

• There is no accepted evidence of life on land at this time

  • Possible terrestrial cyanobacteria, algae, and lichens

  • No evidence for plants on land; no soil available

Fauna

• Diversification of animal groups

  • Possible quick radiation of group called the "Cambrian Explosion"...

    • ...although this pattern may be due to bias in sampling the fossil record (Servais et al. 2023)

  • Animals different in Ediacaran versus early Cambrian

    • Possible extinction event at the beginning of the Cambrian. 

    • Evidence for this extinction event is also found in the carbon excursion used to date the beginning of the Cambrian.

    • Many earlier Ediacaran forms suddenly disappear at the beginning of Cambrian

  • The first coral reefs probably appeared in the Cambrian, 

  • First confirmed hard-shelled animals appeared during the Cambrian, around 530 million years ago. 

    • Trilobites were dominant during Cambrian

  • First vertebrates, such as Myllokunmingia, appeared

  • Soft-bodied fauna have been well-preserved in sediments of the Burgess Shale (505 Ma)

    • Opabinia

      • 5 eyes, a backward-facing mouth underneath its head, and a proboscis extending forward from the head to end in a spined claw

      • Closely related to arthropods

    • Hallucigenia, which was supposed to have rows of rigid spines on which it walked, with tentacles waving at the top. 

      • "Tentacles" then become legs for walking, and the rigid spines possibly a defensive mechanism