Geologic Time Scale Hadean Eon About 4 55

Geologic Time Scale Hadean Eon: About 4. 55 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) 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-1980 s) Credit: Joe Tucciarone. Image used by permission from nasa. gov; rst. gsfc. nasa. gov/Sect 19_2 a. html

Archean Eon: 3. 85 billion to 2. 5 billion Precambrian About 3. 85 billion years ago Oldest rocks The air is rich in nitrogen (N) and carbon dioxide (CO 2) with methane (CH 4), water vapor (H 2 O) and other gases, but very little oxygen (O 2) 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 billion Precambrian About 3. 4 billion years ago First 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 million Precambrian 2. 0 billion years ago Increased concentration of oxygen in the atmosphere from cyanobacteria metabolism (20 steps) Used by permission from Kids. Geo www. kidsgeo. com

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 CO 2 and release O 2 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 53535 A Geologic Time Scale of CT 1. 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 present Paleozoic Era 542 million to 251 million Ordovician Period 488 million to 444 million years ago Bryozoans, first vertebrates appear (5 steps) 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 Geologic Time Scale of CT 520 – 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.

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) A nautiloid fossil (Bickmorites bickmoreanum) from the middle Silurian Period. ©YPM IP 19158 Geologic Time Scale of CT 470 – 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.

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) Used by permission from Florida Center for Instructional Technology, 2009 Geologic Time Scale of CT 440 – 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.

Phanerozic Eon 542 million to present Paleozoic 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) Dragonfly (Meganeuropsis) from The Age of Reptiles Mural by Rudolph F. Zallinger. © 2010 Yale Peabody Museum of Natural History, Yale University Geologic Time Scale of CT 350 – 310 million years ago: The Rheic Ocean disappears as Gondwana collides with Proto North America; massive mountain-building (Alleghenian Orogeny).

Phanerozoic Eon 542 million to present Paleozoic Era 542 million to 251 million 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 R 24134 Geologic Time Scale of CT 310 – 290 million years ago: Gondwana continues to push into Proto North America; continued mountain-building (Alleghenian Orogeny).

Phanerozoic Eon 542 million to present Paleozoic Era 542 million to 251 million 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) Dimetrodon, a synapsid, from. The Age of Reptiles Mural by Rudolph F. Zallinger. © 2010 Yale Peabody Museum of Natural History, Yale University Geologic Time Scale of CT 290 – 270 million years ago: Gondwana stops advancing on Proto North America; Pangaea forms. Eastern pegmatites form.

Phanerozoic Eon 542 million to present Mesozoic 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) Drawn by Margaret M. Colbert. Used by permission from American Museum of Natural History Geologic Time Scale of CT 225 – 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.

Phanerozoic Eon 542 million to present Mesozoic Era 251 million to 65. 5 million Jurassic Period 201. 6 million to 145. 5 million years ago Dinosaurs dominate; flying reptiles appear; first known bird (1. 5 steps) 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. © 2010 Yale Peabody Museum of Natural History, Yale University Geologic Time Scale of CT 200 – 145 million years ago: Atlantic Ocean continues to widen; Hartford Basin stops rifting; Newark Terrane forms (brownstone, sandstone, traprock)

Phanerozoic Eon 542 million to present Mesozoic Era 251 million to 65. 5 million 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 024043 Tyrranosaurus rex with other Cretaceous dinosaurs, the flying reptile Pteranodon, and flowering plants, from. The Age of Reptiles Mural by Rudolph F. Zallinger. Image reflects 1940’s conceptions of dinosaur morphology and habits. © 2010 Yale Peabody Museum of Natural History, Yale University

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; 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.

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 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

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 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

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) By Brian Kell, Public domain, via Wikimedia Commons

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 www. whoi. org

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) 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.

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 (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) © YPM; Neanderthal sculpture by Michael Anderson

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