Phanerozoic eon “Visible Life” Paleozoic Era: old life Mesozoic Era: middle life Cenozoic Era: recent life
Geologic Time scale • 4.6 billion years are divided into big chunks of time called Eons. • Eons are divided into smaller time periods called Eras. • The 3 eras are Paleozoic, Mesozoic, & Cenozoic. • Eras are divided into smaller time periods called Periods. • Periods are further divided into Epochs.
Precambrian Period • Precedes the Cambrian Period • Accounts for 88% of geologic time • Not too much known about this period, and what is has been discovered within the last 50 years • Not many fossils found in this period due to the changing of rocks (metamorphose)
Paleozoic Era • 570 mya to 225 mya • (November and part of December on our calendar) • Longest of the three eras in this eon
A time of Change • This was a time of dramatic geological, climatic and evolutionary change • Cambrian period: witnessed the most rapid and widespread diversification of life in Earth’s history! (Cambrian explosion) • Life began in the ocean, then transitioned on land • By the end of this era it was dominated by various animals
Paleozoic Era: Common Animals • Trilobites were common animals • Sea scorpions (2 m). • Land plants appeared in middle Paleozoic. • Sharks, rays, and bony fish existed. • Tropical jungle like forest were prevalent by the end of the era. • Insects (some huge) were the predominant animals.
Devonian Period Permian Period
Mesozoic Era • 225 mya – 65 mya (Mid December) • “Age of the Reptiles” • Dinosaurs roamed Earth. (mainly non-avian) • Birds and mammals started evolving during the last part of the Mesozoic. • This era began and ended with two mass extinctions: Permian-Triassic event, Cretaceous-Paleogene event
Cenozoic Era • Recent Life (65 mya to present) (Last few days on our calendar.) • “age of mammals” • Ice Age began 3 mya • Took 75000 years to form, stayed 10000 years, then retreated. • Man evolved during this time period • Paleogene, Neogene, Quaternary (periods)