Fossils, & The Geologic Time Scale GEOLOGIC TIME III Fossils, & The Geologic Time Scale

Let’s Take a Closer Look The Geologic Time Scale Earth’s age is believed to be 4.6 billion years It is broken down into different units and sub-units based upon the rocks and fossils within those rock layers Largest division = EON (ex: Archean, Phanerozoic) Next largest = ERA (ex: Mesozoic, Cenozoic) Next largest = PERIOD (ex: Devonian, Jurassic) Smallest division = EPOCH (ex: Miocene, Pleistocene)

The Time Scale Major Units of Time Scale were first constructed in the 1800s Names of these times were usually given by naming them after geographic regions where the rocks from that time were first studied (ex. Pennsylvanian) No absolute dating at that time, so the whole thing was originally done using relative dating Once radiometric dating was discovered, the times were put in place and are continually being checked and refined

Precambrian – 87% of Earth’s History The Precambrian (eon) is made up of 3 large eons totaling over 4 Byrs: Hadean – “hell-like” Archean – “ancient” Proterozoic – “first life” Any information from this time period is sketchy Erosion has destroyed most of the rocks and fossils Any fossils that have survived are rare and simple in structure

Hadean – Hellfire & Brimstone From 4600 – 3800 Mya The formation of the solar system through planetary bombardment Sun was 70% as bright Massive volcanism produces the young atmosphere probably made up of CO2, H2O, CH4, & NH3 No fossils found this old

Archean – oldest rocks From 3800 – 2500 Mya Surface of the earth turns from molten to solid rock Oceans form from water vapor condensation Oldest rocks known have been dated to this eon Potentially the first simple bacteria/algae fossils Noxious atmosphere was very depleted of oxygen Continents begin to form

Proterozoic – big changes From 2500 – 570 Mya Largest Eon (~2 Byrs total) Atmosphere enriches with oxygen due to bacteria—ozone layer forms too (good) Supercontinent Rodinia forms around 800 Mya First multi-cell fossils – simple Stromatolites (algae) Eukaryotic cell fossils Extensive glaciations during “Snowball Earth”

Phanerozoic – “visible life” Three Eras spanning from 570 Mya to present Paleozoic – “ancient life” Mesozoic – “middle life” Cenozoic – “recent life” Greatest diversity of land and ocean organisms Fossil record indicates complex organisms thrive Several mass extinctions We are still currently living in the Phanerozoic

Paleozoic – “Cambrian Explosion” Spans 570 – 245 Mya 7 periods of Paleozoic Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, Permian At the beginning of the Cambrian, the fossil record goes through an exponential increase in diversity and complexity

Burgess Shale (505 mya)

Paleozoic – More specifics 3 distinct “ages” Age of invertebrates (shells) Age of fishes (vertebrates), Age of amphibians Trilobites, seed ferns, & amphibians are major index fossils of the Paleozoic Massive swamps resulting in coal deposits of today Disastrous extinction at the end of the Permian wiping out ~90% of all marine & ~70% of all land organisms

Mesozoic – Rise of Dinosaurs Mesozoic has 3 Periods from 245 – 66 Mya Triassic Jurassic Cretaceous Pangaea begins to break apart and form the current continents Warmer climates dominate Gymnosperms (non-flowering, naked seed) appear and become the dominant plant

Mesozoic – More specifics Reptiles rise, dinosaurs dominate, and shelled eggs help to protect offspring Some reptiles take to the sky (birds) Some reptiles return to the ocean but keep their air lungs (gators, turtles, etc...) The most famous mass extinction in the world occurs at the end of the cretaceous (K/T boundary) Main theory is asteroid impact changed climate so drastically that majority of animals failed to adapt

Cenozoic – Rise of Mammals 2 Periods spanning from 66 Mya to present day Tertiary Quaternary 7 Epochs are contained within the two periods Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, & Holocene We are now in the Holocene Cenozoic has the fossils of the organisms which were able to survive and adapt after the K/T extinction

Cenozoic – More specifics Cenozoic represents less than 2% of Earth’s history Mammals rise and become the dominant organism on land Angiosperms (flowers) become the dominant plant life on land This probably helped to allow the rise of birds and mammals who both feed on flowers and plants Ice age advances occur during Pleistocene Many organisms go extinct with ice age climate changes

To Review: Fossils are the remains or traces of preserved, prehistoric life There are several different ways for fossils to form Fossils give us clues about past environments, past geology, and paleo-climates We can correlate rock layers over distances using fossils The principle of fossil succession says that fossils of the rock record succeed each other in a determinable & definite order The Geologic Time Scale is divided into subdivisions called eons, eras, periods, and epochs The splits between all of these time divisions has been determined by examining both the rocks themselves and the fossils within those layers The divisions represent spans during which the geology & biology have commonalities We are currently in the Phanerozic, the Cenozoic, the Quaternary and the Holocene GMO Rocks

Millions of Years Ago (Mya) EON ERA Millions of Years Ago (Mya) Phanerozoic Eon Cenozoic 66 Mesozoic 245 Paleozoic 570 Precambrian Eon Proterozoic Late Proterozoic 900 Middle Proterozoic 1600 Early Proterozoic 2500 Archean Late Archean 3000 Middle Archean 3400 Early Archean 3800 Hadean 4600

Millions of Years Ago (Mya) EON ERA PERIOD EPOCH Millions of Years Ago (Mya) Phanerozoic Cenozoic Quaternary Holocene 0.01 Pleistocene 1.6 Pliocene 5.3 Tertiary Miocene 23.7 Oligocene 36.6 Eocene 57.8 Paleocene 66.4 Mesozoic Cretaceous 144 Jurassic 208 Triassic 245 Paleozoic Permian 286 Carboniferous Pennsylvanian 320 Mississippian 360 Devonian 408 Silurian 438 Ordovician 505 Cambrian 570 P R E C A M B R I A N T I M E . . .

How will I remember… Eras Periods… Precambrian Paleozoic Mesozoic Cenoozoic Please Pay My Children Cambrian Charlie Ordivocian Oliver Silurian Still Devonian Drives Mississippian My Pennsylvanian Purple Permian Plymouth Triassic To Jurassic Jersey Cretaceous City Tertiary Through Quaternerary Quicksand