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Geologic Time Scale

Hadean Eon: 4.57 billion to 3.85 billion

About 4.5 billion years agoThe formation of the moon and cooling of the Earth (45 steps – see companion activity in the Connecticut Geology curriculum guide, Yale Peabody Museum)

http://rst.gsfc.nasa.gov/Sect19/Sect19_2a.html

Archean Eon: 3.85 billion to 2.5 billionPrecambrian

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 http://www.earthscienceworld.org/image

Archean Eon: 3.85 billion to 2.5 billionPrecambrian

About 3.6 billion years agoFirst cyanobacteria (36 steps)

© YPM 51959

Proterozoic Eon: 2.5 billion to 542 millionPrecambrian

2.0 billion years ago Increased concentration of oxygen in the atmosphere from

cyanobacteria metabolism (20 steps)

Used by permission from KidsGeo www.kidsgeo.com

Proterozoic Eon: 2.5 billion to 542 millionPrecambrian

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 53535A

Geologic Time Scale of CT Proto North America: 1.1 billion years ago (Oldest Rocks in CT)

Avalonian terrane: formed 800-600 million years ago (gneiss and granite)

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

Phanerozoic Eon 542 million to presentPaleozoic Era 542 million to 251 million

Ordovician Period 488 million to 444 million years agoBryozoans, first vertebrates appear

(5 steps)

Geologic Time Scale of CTIapetos Terrane: 500- 300 million yearsBolton Ridge: 500- 300 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.

Used by permission; drawing by Phillipe Janvierhttp://tolweb.org/Astraspida/16906


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 CTIapetos Terrane & Bolton Ridge: 500-300 million years


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 CTIapetos Terrane: 500- 300 million years

Bolton Ridge: 500- 300 million yearsProto North America marble: 400-300 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

Detail, The Age of Reptiles Mural by Rudolph F. Zallinger.

© 2010 Yale Peabody Museum of Natural History, Yale University

Phanerozic Eon 542 million to presentPaleozoic 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)


Proto North America marble: 400-300 million years


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)


Proto North America marble: 400-300 million years

Photo Greg Watkins-Colwell © YPM R24134


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 CTStony Creek granite, eastern pegmatites form

The Age of Reptiles Mural by Rudolph F. Zallinger.


Phanerozoic Eon 542 million to presentMesozoic Era 251 million to 65.5 million

Triassic Period 251 million to 201.6 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


Jurassic Period 201.6 million to 145.5 million years ago

Dinosaurs dominate; flying reptiles appear; first known bird (1.5 steps)

Geologic Time Scale of CTNewark Terrane (Brownstone, sandstone, trap rock): 190 million years

The Age of Reptiles Mural by Rudolph F. Zallinger.



Cretaceous Period 145.5 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 CTShallow sea covers coastal New England; Uplift and erosion inland. Sea level rises until

southern Connecticut is beneath the shallow western Atlantic Ocean.

© YPM VZ 001069

Phanerozoic Eon 542 million to presentCenozoic 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.



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 35228 A Sobalites sp.



Oligocene Epoch 33.9 million to 23 million years ago

First apes (.3 steps)

Used by permission from Wikimedia Commons; http://commons.wikimedia.org/wiki/File:Male_silverback_Gorilla.JPG



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; http://commons.wikimedia.org/wiki/File:Grasslands-menggu.jpg

Used by permission from Woods Hole Oceanographic Institute www.whoi.org



Pliocene Epoch 5.3 million to 2.6 million years ago

Panama land bridge forms (.05 steps)


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.

© YPM; sculpture by Michael Anderson


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)

Used by permission from U.S. Coast Guard;

Image source: National Snow and Ice Data Center


Quaternary Period 2.6 million to presentHolocene 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)

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