Ordovician Period

Age of the earliest land plants

The Ordovician Period (485-444 Ma) is in the Paleozoic Era, occurring after the Cambrian Period and before the Silurian Period.

Late Ordovician: 458.4–443.8 million years ago
- Hirnantian: 445.2±1.4–443.8±1.5 Ma
- Katian: 453.0±0.7–445.2±1.4 Ma
- Sandbian: 458.4±0.9–453.0±0.7 Ma
Middle Ordovician: 470.0–458.4 million years ago
- Darriwilian: 467.3±1.1–458.4±0.9 Ma
- Dapingian: 470.0±1.4–467.3±1.1 Ma
Early Ordovician: 485.4–470.0 million years ago
- Floian: 477.7±1.4–470.0±1.4 Ma
- Tremadocian: 485.4±1.9–477.7±1.4 Ma

- The carbon dioxide levels hover around ~5,000 ppm during this Period
- Oxygen levels are relatively stable during this time at 17%
- The Taconic progeny forms a mountain chain formed from eastern Canada down through the East coast of the United States
  - Portions of the range are represented by the Appalachian Mts

Algae were dominant in the oceans
- Probable autotrophs on the land, such as soil algae or bacteria
Evidence for the earliest land plants
- Spores from land plants in the Early Ordovician indicating the presence of bryophytes and eophytes
- Potential macro-fossil evidence of liverworts, hornworts, and mosses by the Middle Ordovician (Retallack, 2019)
- The appearance of early land plants may have helped trigger the 2nd largest glaciation event (Lenton et al., 2012)

Mycorrhizal fungi, related to the glomeromycetes, are found in associated with land plants and

Terrestrial fungi-like organisms, such as Prototaxites, are some of the largest organisms on the landscape at 15 cm tall