Late Ordovician

What happened during this time?

Geophysical

• Late Ordovician Glaciation

  • At least two glaciation events over 447-444 Ma

    • End of Katian event; end of Hirnantian event

    • Each glaciation thought to last between 0.5-1.5 Ma

    • Sea levels frequently rise and fall during these glaciations

  • Volcanic activity created silicates that absorbed CO2 from the atmosphere

    • Carbon dioxide levels dropped from 7,000 ppm to 4,400 ppm

  • Ocean anoxia

• Earth may have possessed a ring, like Saturn, during the Late Ordovician (Tomkins et al., 2024)

Biological

• • Second largest extinction in Earth's history

    • First extinction of the "big five extinctions"

• 50-60% of marine life goes extinct; maybe as high as 85%

  • Reducing conditions, with low to no oxygen and little to no hydrogen sulfide levels, are probably playing a much more important role in this extinction (Kozik et al., 2022)

• The appearance of early land plants (bryophytes, eophytes?) may have triggered the 2nd largest glaciation event (Lenton et al., 2012; Retallack, 2015)

  • Increased weathering of rocks that absorb carbon dioxide levels

  • Carbon is buried in deep-sea sediments which dropped global CO2 levels

• The earliest putative evidence of stomata comes from this time from Zbrza, Poland (Salamon et al., 2018; Clark et al., 2022)

• Putative branched sporophytes have been described from 445 Ma (Salamon et al. 2018)

  • The preservation of these fossils makes it difficult to know if they had vascular tissue