Overview - Timescale, Physical Landscapes

Ordovician plate tectonics brought major changes in climate and biological systems. Rapid seafloor spreading along ridges caused the highest sea levels in the Phanerozoic. As a result, continents were subjected to unprecedented flooding and at times North America was almost completely submerged.

• 485.4 - 443.8 ma
  
• Division of Paleozoic era
  

Phanerozoic Eon

• Paleozoic era
  
  • Orodvician Period
    
    • Lower
      
      • Tremadocian
        
      • Floian
        
      
      
      
    • Middle
      
      • Dapingian
        
      • Darriwilian
        
      
      
      
    • Upper
      
      • Sandbian
        
      • Katian
        
      • Hirnantian
        
      
      
      
    
    
    
  
  
  

Numerical modeling of the Ordovician atmosphere estimates that the concentration of carbon dioxide was several times higher than today. At the end of the Ordovician, most of the Southern Hemisphere experienced a brief period of major glaciation.

During the Ordovician, there were four large continents separated by three large oceans. The Laurentian craton was above the equator and rotated clockwise by about 45° from its present orientation. South of the two continents was the Iapetus Sea, separating the Baltic craton, which included present-day Scandinavia and north-central Europe. West of Baltica, facing Laurentia across the Iapetus Sea, was a small continent called Avalonia, which included England, New England and continental Canada. This huge supercontinent covered both Antarctica, what is now northwest Africa, and the equator, which cuts across what is now Australia and Antarctica. At that time, Africa and South America were rotated about 180 degrees from their present orientation. Almost the entire northern hemisphere was covered by a single body of water.