artist’s conception of a smaller planetary body colliding with earth, leading to the formation of...

Artist’s conception of a smaller planetary body colliding with Earth, leading to the formation of the moon (the Giant Impactor Theory, widely accepted since the mid-1980s)

Credit: Joe Tucciarone. Image used by permission from nasa.gov; rst.gsfc.nasa.gov/Sect19/Sect19_2a.html

Geologic Time Scale

Hadean Eon: About 4.55 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 3.85 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/images

Archean Eon: 3.85 billion to 2.5 billionPrecambrian

About 3.4 billion years agoFirst cyanobacteria (34 steps)

Stromatolite fossil specimen from the Yale Peabody Museum Paleobotany Division. Stromatolites are natural formations that occur in shallow water and are the result of layers of sediment being

cemented together by biofilms of cyanobacteria and other microorganisms.© 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)

Stromatolite fossil specimen from the Yale Peabody Museum. This specimen has been sliced in half and polished to reveal the interior. Cyanobacteria are the most likely microorganisms involved in the formation of stromatolites like this one.

© YPM 53535A

Geologic Time Scale of CT1.1 billion years ago: Proto North America (approx. age of the oldest rocks in CT); the land mass that

would eventually form the westernmost part of CT was in the middle of the supercontinent Rodinia 600 – 550 million years ago: Rodinia rifts apart, leaving western CT at the edge of the Iapetos Ocean

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) A trilobite fossil (Cambropallas telesto) from the

early Cambrian Period. © 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 CT520 – 470 million years ago: Iapetos Ocean grows in size, and then towards the end of this time period begins to close; Taconic Island Arc forms in the middle of the Iapetos Ocean and

begins moving towards Proto North America; on the far side of the Iapetos Ocean, Avalonia rifts away from the rest of Gondwana and begins moving towards Proto North America.

Artist’s conception of an astraspid (Astraspis desiderata). Astraspids were a small group of armored, jawless vertebrates from the middle Ordovician Period. Used by permission; drawing by Phillipe Janvier, http://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)

A nautiloid fossil (Bickmorites bickmoreanum) from the middle Silurian Period. ©YPM IP 19158

Geologic Time Scale of CT470 – 440 million years ago: Taconic Island Arc collides with Proto North America and creates

mountains (Taconic Orogeny); Avalonia continues to move towards Proto North America; Rheic Ocean between Avalonia and Gondwana expands.


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 CT440 – 400 million years ago: Taconic Mountains erode and Avalonia continues to move

towards Proto North America.400 – 350 million years ago: The Iapetos Ocean disappears as Avalonia collides with Proto

North America; oceanic crust is pushed into the continent, causing the seafloor muds to metamorphose into gneiss and schist. Volcanic island arcs and distinct regions of the Iapetos

Ocean form geologic terranes in New England. The Rheic Ocean starts to close, and Gondwana begins to move towards Proto North America.

Used by permission from Florida Center for Instructional Technology, 2009

Dragonfly (Meganeuropsis) from 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

Carboniferous Period 359 million to 299 million

Mississippian Epoch 359 million to 318 million years ago

High oxygen levels (25-30% compared to 21% today) allow insects like dragonflies to grow large (50 cm wingspan!) despite primitive respiratory systems; ferns common; frogs develop. Great swamps form coal deposits

around the world. (3.5 steps)

Geologic Time Scale of CT350 – 310 million years ago: The Rheic Ocean disappears as Gondwana collides

with Proto North America; massive mountain-building (Alleghenian Orogeny).


Carboniferous Period 359 million to 299 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)

Marine iguana (Amblyrhynchus cristatus) from the Galapagos Islands, Ecuador. Photo Greg Watkins-Colwell © YPM R24134

Geologic Time Scale of CT310 – 290 million years ago: Gondwana continues to push into Proto North

America; continued mountain-building (Alleghenian Orogeny).


Permian Period 299 million to 251 million years ago

Synapsids, a group of animals that included the ancestors of mammals, flourished in the Permian Period. Pangaea forms. Mass extinction, especially of marine life, at end of Permian. (2.5 steps)

Geologic Time Scale of CT290 – 270 million years ago: Gondwana stops advancing on Proto North America;

Pangaea forms. Eastern pegmatites form.

Dimetrodon, a synapsid, fromThe 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 a

meteorite impact or huge volcanic eruption, eliminating the large land reptiles and allowing dinosaurs to expand. Dinosaurs appear; first mammals (small,

rodent-like creatures). Pangaea begins to rift apart. (2 steps)

Geologic Time Scale of CT225 – 200 million years ago: Pangaea begins to rift apart. Atlantic Ocean begins to grow as Africa moves

East; Hartford Basin forms in an adjacent rift valley.

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 CT200 – 145 million years ago: Atlantic Ocean continues to widen; Hartford Basin stops rifting;

Newark Terrane forms (brownstone, sandstone, traprock)

Left: Apatosaurus and Stegosaurus, two of the most iconic dinosaurs of the Jurassic Period. Right: Close-up of a flying reptile (Rhamphorhynchus). Both images from The Age of Reptiles Mural by Rudolph F. Zallinger; images reflect 1940’s conceptions of dinosaur morphology and habits.



Cretaceous Period 145.5 million to 65.5 million years ago

First snakes; first grasses and flowering plants appear; mass extinction of dinosaurs about 65 million years ago

(.6 steps)

Pacific boa (Candoia carinata). © YPM VZ 024043Tyrranosaurus rex with other Cretaceous dinosaurs, the flying

reptile Pteranodon, and flowering plants, fromThe Age of Reptiles Mural by Rudolph F. Zallinger. Image reflects 1940’s

conceptions of dinosaur morphology and habits.


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; many new mammal species; earliest whales and dolphins; first bats; first large land mammals (.5 steps)

A pair of early horse-like mammals (Merychippus) from 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

At the beginning of the Eocene, Earth much warmer than today; climate at north and south poles similar to modern-day Pacific Northwest (like Seattle, Washington); rainy, tropical climate and semi-tropical plants in Wyoming.

(.4 steps)

A leaf fossil from an extinct fan palm (Sabalites sp.) collected in Lincoln County, Wyoming, USA. © YPM 35228 A



Oligocene Epoch 33.9 million to 23 million years ago

First ape-like primates (.3 steps)

Aegyptopithecus zeuxis skull cast from the Yale Peabody Museum Vertebrate Paleontology collection. Aegyptopithecus is an early member of the group that led to apes. The original specimen was collected in Egypt. © YPMVP 23975



Miocene Epoch 23 million to 5.3 million years ago

First grassland ecosystems during the middle Cenozoic Era (.25 steps)

By Brian Kell, Public domain, via Wikimedia Commons

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)

Mammoth (Mammuthus sp.) from 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; Neanderthal sculpture by Michael Anderson


Quaternary Period 2.6 million to present

Pleistocene Epoch 2.6 million to 10 thousand years ago

Neanderthals (Homo neanderthalensis) existed at least 300,000 years ago and went extinct about 30,000 years ago. Anatomically recognizable modern

humans (Homo sapiens) appeared about 200,000 years ago. (.001 steps)

Glacier flowing into Prince William Sound, Alaska. Used by permission: Department of the Interior/USGS


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)

artist’s conception of a smaller planetary body colliding with earth, leading to the formation of...

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