BIO2 Lesson 3 - Geologic Time Scale

GEOLOGIC TIME SCALE

• Earth's history divided into units: eons, eras, periods, and epochs.

EONS AND ERAS

• Precambrian Eons (before Cambrian Explosion):

  • Hadean (4.6 billion years ago)

  • Archean (3.6 billion years ago)

  • Proterozoic (2.6 billion years ago)

• Phanerozoic Eon (541 million years ago - present):

  • Paleozoic Era:

    • Cambrian explosion marked the emergence of major phyla (approx. 50).

    • Major developments: emergence of marine life, first terrestrial vertebrates, amphibians, reptiles, and mammals.

    • Mass extinction events, e.g., Permian Mass Extinction (wiped out 70% land and 96% marine species).

  • Mesozoic Era:

    • Dominance of dinosaurs, diversification of reptiles and small mammals.

    • K-T extinction due to possible asteroid impact, leading to the loss of many species including non-avian dinosaurs.

  • Cenozoic Era:

    • Tertiary Period: recovery and diversification of mammals.

    • Quaternary Period: includes the Pleistocene (ice age) and Holocene (present time).

TYPES OF FOSSILS

• Trace Fossil: Indirect evidence (e.g., footprints, burrows).

• Molds and Casts: Impressions of organisms and molds filled with materials.

• Original Material: Actual preserved remains of organisms (e.g., amber).

• Petrification: Original organic material replaced with minerals (petrified wood).

• Mummification/Freezing: Preserved remains through extreme conditions.