Introduction to Geologic Time

(The Rock Record is Like a Chart Recorder Output)

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4600 Ma Formation of Earth and Moon

3800 Hadean/Archean (Oldest terrestrial rock)

• First Stromatolites (possible remains of life)
• First probable microorganisms

2500 Archean/Proterozoic

• Oldest probable blue-green algae
• Oldest multi-celled organisms

538 Proterozoic/Paleozoic (oldest skeletal remains--shells)

• First vertebrates--jawless fish
• First jawed fish
• First reptiles

245 Paleozoic/Mesozoic (mass extinction)

• First dinosaurs
• First mammals

66 Mesozoic/Cenozoic (mass extinction)

• First hominids

2 Tertiary/Quaternary (and Pleistocene)

• Early Homo sapiens

0.011 Pleistocene/Holocene (end of last Ice Age)

Two ways to view geologic time:

• Relative time: "older" vs. "younger" placed in order
• Absolute time: "120 Ma" (Ma = million years; also m.y.)

The Geologic Time Scale (relative time)

• Eons, eras, periods, epochs
• Major divisions based on biologic events

The Geologic Periods

• Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian. Triassic, Jurassic, Cretaceous
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