300 million years ago, the landmass Laurentia collided with Baltica. The Appalachian mountains of eastern North America rose along the edges of the supercontinent, Pangea, and a climate shift thrust the Earth into an ice age. Map courtesy of CR Scotese, PALEOMAP Project
      • Pangea supercontinent forms as all continents collide – significant mountain building worldwide;
      • High sea levels form broad, shallow continental seas and vast coal swamps;
      • Climate hot & humid but glaciated at the poles;
      • Oxygen level 40% above today – abundant wildfires;
      • Much of the world’s coal formed in the Carboniferous;
      • Reptiles appear and diversify wildly; first ancestor of mammals appears.


Name Diameter (km) Age (megayears) Dating method Morphological type Notes
Ile Rouleau, Quebec 4 <300 Geological dating CONFIRMED Complex Age based on stratigraphy
Middlesboro, Kentucky 6 <300 Geological dating CONFIRMED Complex Dates to the formation of the supercontinent Pangaea 300 million years ago