The formation of the isthmus connecting North and South America and the split of the Australian continent from Antarctica changed global ocean currents and climate. Ice sheets carved out the Great Lakes of the United States and Canada just 20,000 years ago. Since then, warmer temperatures have melted ice, and sea levels have risen. Map courtesy of CR Scotese, PALEOMAP Project
  • Continents & oceans in current position;
  • Four major glacial advances (ice covered up to 30% of Earth’s surface) followed by interglacial warming;
  • Sea levels drop & rise as glaciers advance and melt;
  • Climate cold & dry world-wide;
  • Epoch ends in mass extinction; esp of megafauna;
  • All modern plant & animal families present, land & sea;
  • Large mammals (megafauna) thrive;
  • Tool-using pre-humans appear in Africa & spread throughout the Old World;
  • Neanderthal humans appear then disappear;
  • Modern humans (Homo sapiens) first appear.


Name Diameter (km) Age (megayears) Dating method Morphological type Notes
Pingualuit, Quebec 3.44 1.4 ± 0.1 Ar40-Ar39 melt rock CONFIRMED Simple Overflight of Pingualuit Crater
Barringer, Arizona 1.19 0.049 ± 0.003 Radioactive decay CONFIRMED Simple Jointed
Haviland, Kansas 0.01 0.02  ±0.002 Geological dating CONFIRMED Simple Brenham meteorite