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

3. 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)

4. 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

5. 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

6. 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

7. 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

8. 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”

9. 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

10. 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

11. 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
Supercontinents Laurasia, Gondwanaland, and eventually Pangaea form
Disastrous extinction at the end of the Permian wiping out ~90% of all marine & ~70% of all land organisms

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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 . . .

19. How will I remember this???
Eras: Precambrian, Paleozoic, Mesozoic, Cenozoic
Peter Piper Milks Cows
Periods: Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, Permian, Triassic, Jurassic, Cretaceous, Tertiary, Quaternary
Charlie Oliver Still Drives My Purple Plymouth to Jersey City through Quicksand

20. How will I remember this?
Epochs of the Cenozoic: Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, Holocene
Pigeon egg omelets make people puke heartily