Location
 Worldwide
 390 million years ago

Mean atmospheric O₂
 75% of modern level

Mean atmospheric CO₂
 8x pre-industrial level

Mean temperature
 6°C above modern level

 

Arborescent (tree-like) horsetails of the genus Calamites of varying size (10 to 50 feet tall) populate lowlands near the brackish waters of an inland sea 390 million years ago. Closer to the ground at about 6 feet tall is a variety of Drepanophycus, a genus of the division Lycopodiophyta, ancient plants that preceded the Calamites by about 20 million years and coexisted with them for 35 million years.