Geologic Time Scale Notes

Relative Time: History of the Earth Through Deep Time

Stratigraphy

• The study of strata.
• Strata are layers of rock; one layer is a stratum.
• Stratigraphy includes understanding texture, composition, arrangement, and correlation of rock bodies.
• The layers of strata tell a story about Earth’s history.
• Each layer is like a page corresponding to a portion of time.
• Each layer records events that happened during that time

Geologic Time

• James Hutton (1726-1797) was one of the first people to recognize the vastness of geologic time.
• He realized that the time needed for sediments to be deposited, buried, cemented, uplifted, and eroded must be great, unless these processes happened much faster in the past than they do today.

Hutton’s Principle of Uniformitarianism

• The geologic processes occurring on Earth today have operated uniformly in the past and will continue to operate that way in the future.

Measuring Time

• Relative Dating
  • Places events in sequential order
  • Not reliant on knowing numerical ages
• Numerical Dating
  • Specific events dated, usually using radioactive decay of an isotope system.
  • The geologic time scale is a fusion of relative and numerical time

Geologic Time Scale

• Earth’s history is divided into categories of different sizes.
• Hierarchical system where the uppermost rank is most inclusive, and each subsequent rank has fewer ranks within it.
• The rank of eon contains eras, which contain periods, which contain epochs, which contain ages; the rank of epoch only contains ages.

Units in Geochronology and Stratigraphy

GSA Geologic Time Scale v. 5.0

• Presents a detailed chart of the Geologic Time Scale, including Eons, Eras, Periods, Epochs, and Ages.
• Includes numerical ages (Ma) for various boundaries and picks.
• References the International Chronostratigraphic Chart and the International Commission on Stratigraphy.
• Cenozoic Era:
  • Quaternary Period:
    • Holocene Epoch: 0.0042 - 0.0117 Ma
    • Pleistocene Epoch: 0.0117 - 2.58 Ma
  • Neogene Period:
    • Pliocene Epoch: 2.58 - 5.333 Ma
    • Miocene Epoch: 5.333 - 23.03 Ma
  • Paleogene Period:
    • Oligocene Epoch: 23.03 - 33.9 Ma
    • Eocene Epoch: 33.9 - 56.0 Ma
    • Paleocene Epoch: 56.0 - 66.0 Ma
• Mesozoic Era:
  • Cretaceous Period: 66.0 - 145.0 Ma
  • Jurassic Period: 145.0 - 201.3 Ma
  • Triassic Period: 201.3 - 251.902 Ma
• Paleozoic Era: 251.902 - 541.0 Ma
  • Permian Period: 251.902 - 298.9 Ma
  • Carboniferous Period: 298.9 - 358.9 Ma
  • Devonian Period: 358.9 - 419.2 Ma
  • Silurian Period: 419.2 - 443.8 Ma
  • Ordovician Period: 443.8 - 485.4 Ma
  • Cambrian Period: 485.4 - 541.0 Ma
• Precambrian:
  • Neoproterozoic Era: 541.0 - 1000 Ma
  • Mesoproterozoic Era: 1000 - 1600 Ma
  • Paleoproterozoic Era: 1600 - 2500 Ma
  • Archean Eon: 2500 - 4000 Ma
  • Hadean Eon: 4000 - ~4600 Ma

Eons

• Eons are the longest divisions of Earth’s history
• Phanerozoic: $541$ Ma - present
• Proterozoic: $2.5$ Ga - $541$ Ma
• Archean: $4.0$ Ga - $2.5$ Ga
• Hadean: $4.6$ Ga - $4.0$ Ga

Hadean Eon

• $4.6$ to $4.0$ billion years ago
  • Earth coalescing
  • Water
  • Moon
  • Core Accretion
  • Magnetic Field
  • Late Bombardment Stage

Archean Eon

• $4.0$ to $2.5$ billion years ago
  • First Oceans
  • DNA
  • Tectonic Activity
  • First Continent
  • Prokaryote Bacteria
  • Banded Iron Formation
  • Great Oxygenation Event

Proterozoic Eon

• $2500$ to $541$ million years ago
  • Oxygen Crisis
  • First Eukaryotes
  • Snowball Earth
  • Multicellular Life
  • Ozone Stabilization

Eras

• Eons are divided into eras
• Phanerozoic has three
• Proterozoic has three
• Archean has four
• Hadean has none

Phanerozoic Eon

• Divided into 3 eras:
  • Cenozoic ($66$ Ma - now)
  • Mesozoic ($252$ Ma - $66$ Ma)
  • Paleozoic ($541$ Ma - $252$ Ma)
    *The periods of the Cenozoic are Paleogene, Neogene, Quaternary

Periods

• Eras are divided into periods
• Cenozoic has three
• Mesozoic has three
• Paleozoic has seven
• Proterozoic has ten

Paleozoic Era

• $540$ - $252$ Million Years Ago
  • Age of Invertebrates
  • Cambrian Explosion
  • Age of Fish
  • Land Plants
  • Insects
  • Age of Amphibians
  • Fungi
  • Coal Deposits
  • Extinction

Mesozoic Era

• $252$ to $66$ million years ago
  • Age of Reptiles
  • Pangea
  • Age of Conifers
  • Age of Dinosaurs
  • Birds
  • Small Mammals
  • Flowering Plants

Cenozoic Era

• $66$ to $0$ million years ago
  • Dinosaur Extinction (non-avian)
  • Primates
  • Modern Earth
  • Stone Age
  • Cities
  • Age of Mammals
  • Grass
  • Apes
  • Homo Sapiens

Mnemonics: Paleozoic

• Permian
• Pennsylvanian
• Mississippian
• Devonian
• Silurian
• Ordovician
• Cambrian
• Mnemonic: "Pontiac Purple My Drive Smack On Cats"

Mnemonics: Mesozoic

• Cretaceous
• Jurassic
• Triassic
• They're in alphabetical order from youngest to oldest

Mnemonics: Cenozoic

• Quaternary
• Neogene
• Paleogene
• Mnemonic: "Mind your Ps & Qs"
• $66$ Ma

Mnemonics: Cenozoic Epochs

• Holocene
• Pleistocene
• Pliocene
• Miocene
• Oligocene
• Eocene
• Paleocene
• Mnemonic: "Hood Pontiac’s Purple My On Eat People" (note: people not on exam, just for fun)