The Cenozoic Era

Image of mammals during the Miocene Epoch of the Cenozoic Era
Rendering of possible scene during the Miocene Epoch
North America 60 million years ago
North America 60 million years ago
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The Cenozoic Era is the present geological era on Earth. It began about 65 million years ago, about the same time an asteroid impacted the planet in what is now the Gulf of Mexico and marked the ending of the Age of the Dinosaurs with a global forest fires and a vast cloud of iridium dust. That dust settled back to Earth and formed a thin white line that can still be seen in areas in southern Colorado and northern New Mexico.

The Cenozoic is the Age of Mammals as they have grown to dominate the planet.

Map of North America during the Ice Ages
North America about 25,000 years ago
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The Age of Mammals

Eons, Eras, Periods & Events Millions of years ago Notes
Quaternary Period
  • Holocene
  • Pleistocene
Present-2 Marked by increases and decreases in global glaciation, Bering Land Bridge. The beginnings of Man, minor mass extinctions continue around the globe
Neogene Period
  • Miocene
  • Pliocene
2-23 North America crashes into South America, Isthmus of Panama rises, Antarctica ices over, glaciers spread across high mountains and polar oceans.
Mountain building 15-30 Vulcanism and mountain building in western North America: the modern Rockies are built, Basin & Range Province is built, Coast Ranges are pushed up
Paleogene Period
  • Oligocene
  • Eocene
  • Paleocene
23-65 Paleocene-Eocene Thermal Maximum Extinction Event: 55.5 million years ago.
Eocene Maximum Thermal Event: 47 million years ago. Last major global warming event
Laramide and Sevier Orogenies 63-65 Overlapping mountain building events in the western US and Canada along the Cordillera and to the west: the Ancestral Rockies and the Colorado Plateau pushed up
Cretaceous-Paleogene Extinction Event, K-T Boundary 65 Asteroid impact near the Yucatan peninsula, postulated to have combined with on-going geological and atmospheric processes to cause global climatic conditions that wiped out the dinosaurs
Mammals of the early Pleistocene Epoch
Mammals of the early Pleistocene
The iridium marker at the K-T Boundary
The thin white layer above the coal, below the sandstone is the iridium marking the K-T Boundary
Upper image is in the public domain
Maps are © Ron Blakey, NAU Geology,
Lower image courtesy of The Public Library of Science, CCA 3.0 License
Bottom photo courtesy of TheArmchairExplorer, CCA-by-SA 3.0 License