1. Hadean Eon: 4.57 billion to 3.85 billion
Geologic Time Scale
Hadean Eon: 4.57 billion to 3.85 billion
About 4.5 billion years ago
The formation of the moon and cooling of the Earth (45 steps – see companion activity in the Connecticut Geology curriculum guide, Yale Peabody Museum)
Image used by permission from nasa.gov; rst.gsfc.nasa.gov/Sect19/Sect19_2a.html

2. Archean Eon: 3.85 billion to 2.5 billion About 4 billion years ago
Precambrian
About 4 billion years ago
Oldest rocks
The air is rich in nitrogen (N) and carbon dioxide (CO2) with methane (CH4), water vapor (H2O) and other gases, but very little oxygen (O2) is present. (38 steps)
Used by permission from National Oceanic & Atmospheric Administration; Image source: Earth Science World Image Bank

3. Archean Eon: 3. 85 billion to 2. 5 billion Precambrian About 3
Archean Eon: 3.85 billion to 2.5 billion Precambrian About 3.6 billion years ago First cyanobacteria (36 steps)
© YPM

4. Proterozoic Eon: 2.5 billion to 542 million
Precambrian
2.0 billion years ago 
Increased concentration of oxygen in the atmosphere from cyanobacteria metabolism (20 steps)
Used by permission from KidsGeo

5. Proterozoic Eon: 2.5 billion to 542 million Precambrian
1.6 billion years ago 
Photsynthesizing organisms (cyanobacteria and plankton) thrive in shallow seas. These organisms continue to metabolize CO2 and release O2 into the air as a by-product. (16 steps)
© YPM A
Geologic Time Scale of CT
Proto North America: 1.1 billion years ago (Oldest Rocks in CT)
Avalonian terrane: formed million years ago (gneiss and granite)

6. Phanerozoic Eon 542 million to present
Paleozoic Era 542 million to 251 million
Cambrian Period 542 million to 488 million years ago
The “Cambrian Explosion” of marine animals – many animals inhabit the shallow, calcareous-mud bottom of warm shallow oceans along the edges of the continent, including westernmost Connecticut.
Abundant hard-shelled trilobites appear in the sea
(6 steps)
© YPM IP 37621

7. Phanerozoic Eon 542 million to present
Paleozoic Era 542 million to 251 million
Ordovician Period 488 million to 444 million years ago
Bryozoans, first vertebrates appear
(5 steps)
Used by permission; drawing by Phillipe Janvier
Geologic Time Scale of CT
Iapetos Terrane: million years
Bolton Ridge: million years
480 million years – Western Connecticut rises as ocean volcanic rocks are pushed into the ancient continent. The eastern two-thirds of the state remain under an ancient ocean called Iapetos.

8. Phanerozoic Eon 542 million to present
Paleozoic Era 542 million to 251 million
Silurian Period 444 million to 416 million years ago
Nautiloids common. Oxygen levels in the air are at about 10 percent.
(4.5 steps)
©YPM IP 19158
Geologic Time Scale of CT
Iapetos Terrane & Bolton Ridge: million years

9. Phanerozoic Eon 542 million to present
Paleozoic Era 542 million to 251 million
Devonian Period 416 million to 359 million years ago
First sharks; earliest terrestrial animals, amphibians and wingless insects appear (4 steps)
Geologic Time Scale of CT
Iapetos Terrane: million years
Bolton Ridge: million years
Proto North America marble: million years
The Iapetos Ocean is destroyed as its crust is pushed into the continent, causing the seafloor muds to metamorphose into gneiss and schist. Granites rising in the crust of west-central Connecticut also metamorphose. Volcanic island arcs and distinct regions of the Iapetos Ocean form the geologic zones of New England known as terranes.
Used by permission from Florida Center for Instructional Technology, 2009

10. Phanerozic Eon 542 million to present
Paleozoic Era 542 million to 251 million
Mississippian Epoch 359 million to 318 million years ago
Huge dragonflies (50 cm wingspan!); ferns common; frogs develop. Great swamps form coal deposits around the world.
(3.5 steps)
Detail, The Age of Reptiles Mural by Rudolph F. Zallinger.
© 2010 Yale Peabody Museum of Natural History, Yale University
Geologic Time Scale of CT
Iapetos Terrane: million years
Proto North America marble: million years

11. Phanerozoic Eon 542 million to present
Paleozoic Era 542 million to 251 million
Pennsylvanian Epoch 318 million to 299 million years ago
Appalachian Mountains formed; first conifers appear; coal deposited in eastern Ohio; first sauropsids (the group of organisms that gave rise to reptiles) (3 steps)
Geologic Time Scale of CT
Iapetos Terrane: million years
Proto North America marble: million years
Photo Greg Watkins-Colwell © YPM R24134

12. Phanerozoic Eon 542 million to present
Paleozoic Era 542 million to 251 million
Permian Period 299 million to 251 million years ago
Warm-blooded reptiles, forerunners of mammals, appear. Very high levels of oxygen (30% compared to 21% today) allow huge insects to fly despite primitive respiratory systems. Pangaea forms. Mass extinction, especially of marine life, at end of Permian. (2.5 steps)
Geologic Timescale of CT
Stony Creek granite, eastern pegmatites form
The Age of Reptiles Mural by Rudolph F. Zallinger.
© 2010 Yale Peabody Museum of Natural History, Yale University

13. Phanerozoic Eon 542 million to present
Mesozoic Era 251 million to 65.5 million
Triassic Period 251 million to million years ago
Life takes tens of millions of years to recover from the Permian-Triassic extinction. More extinction marks the end of the Triassic, possibly due to meteor impacts or volcanic events. This eliminates the large land reptiles and clears the way for dinosaurs to expand. Dinosaurs appear; first mammals (small, rodent-like creatures)
(2 steps)
Drawn by Margaret M. Colbert. Used by permission from American Museum of Natural History

14. Phanerozoic Eon 542 million to present
Mesozoic Era 251 million to 65.5 million
Jurassic Period million to million years ago
Dinosaurs dominate; flying reptiles appear; first known bird
(1.5 steps)
Geologic Time Scale of CT
Newark Terrane (Brownstone, sandstone, trap rock): 190 million years
The Age of Reptiles Mural by Rudolph F. Zallinger.
© 2010 Yale Peabody Museum of Natural History, Yale University

15. Phanerozoic Eon 542 million to present
Mesozoic Era 251 million to 65.5 million
Cretaceous Period million to 65.5 million years ago
Rocky Mountains began to form; first snakes; first grasses and flowering plants appear; mass extinction of dinosaurs about 65 million years ago
(.6 steps)
Geologic Time Scale of CT
Shallow sea covers coastal New England; Uplift and erosion inland. Sea level rises until southern Connecticut is beneath the shallow western Atlantic Ocean.
© YPM VZ

16. Phanerozoic Eon 542 million to present
Cenozoic Era 65.5 million to present
Tertiary Period 65.5 million to 2.6 million
Paleocene Epoch 65.5 million to 55.8 million years ago
Himalayas began to form; large radiation of mammals; earliest whales and dolphins; first bats; first large land mammals (.5 steps)
The Age of Mammals, a mural by Rudolph F. Zallinger.
Copyright © 1966, 1975, 1989, 1991, 2000 Peabody Museum of Natural History, Yale University, New Haven, Connecticut, USA. All rights reserved.

17. Phanerozoic Eon 542 million to present
Cenozoic Era 65.5 million to present
Tertiary Period 65.5 million to 2.6 million
Eocene Epoch 55.8 million to 33.9 million years ago
Semi-tropical plants in Wyoming at the beginning of the Eocene
(.4 steps)
© YPM A Sobalites sp.

18. Phanerozoic Eon 542 million to present
Cenozoic Era 65.5 million to present
Tertiary Period 65.5 million to 2.6 million
Oligocene Epoch 33.9 million to 23 million years ago
First apes (.3 steps)
Used by permission from Wikimedia Commons;

19. Phanerozoic Eon 542 million to present
Cenozoic Era 65.5 million to present
Tertiary Period 65.5 million to 2.6 million
Miocene Epoch 23 million to 5.3 million years ago
First grassland ecosystems during the middle Cenozoic Era
(.25 steps)
Used by permission from Wikimedia Commons;

20. Phanerozoic Eon 542 million to present
Cenozoic Era 65.5 million to present
Tertiary Period 65.5 million to 2.6 million
Pliocene Epoch 5.3 million to 2.6 million years ago
Panama land bridge forms (.05 steps)
Used by permission from Woods Hole Oceanographic Institute

21. Phanerozoic Eon 542 million to present
Cenozoic Era 65.5 million to present
Quaternary Period 2.6 million to present
Pleistocene Epoch 2.6 million to 10 thousand years ago
Dramatic changes in climate; ice sheets cover and uncover Connecticut.
Ice ages, mammoths, and mastodons (.01 steps)
The Age of Mammals, a mural by Rudolph F. Zallinger.
Copyright © 1966, 1975, 1989, 1991, 2000 Peabody Museum of Natural History, Yale University, New Haven, Connecticut, USA. All rights reserved.

22. Phanerozoic Eon 542 million to present
Cenozoic Era 65.5 million to present
Quaternary Period 2.6 million to present
Pleistocene Epoch 2.6 million to 10 thousand years ago
Neanderthals existed, 130,000 years ago (.001 steps)
© YPM; sculpture by Michael Anderson

23. Phanerozoic Eon 542 million to present
Cenozoic Era 65.5 million to present
Quaternary Period 2.6 million to present
Holocene Epoch 10 thousand years ago to present
Most recent ice age ends about 10,000 years ago. The climate rapidly warms up to its present state, and plants and animals familiar to us today inhabit our landscape. “Neolithic” period of human history
(.0001 steps)
Used by permission from U.S. Coast Guard;
Image source: National Snow and Ice Data Center