Earliest life forms were influenced by: The forming atmosphere and oceans Volcanic activity Mountain building Influence of Catastrophes on Earth’s History

Geologic Time Scale- is a record of the major events and diversity of life forms present in Earth’s history. At the end of each era, a mass extinction occurred

Dividing Geological Time o Pre-Cambrian Time – period where geological time begins –Covers 88% of Earth’s history o Ended 542 MILLION years ago –Divided into 3 eras; long units of time Paleozoic Era, Mesozoic Era, and Cenozoic Era

Dividing Geological Time o Eras are subdivided into units of geological time called periods. –Triassic Period, Jurassic Period, and Cretaceous Period

Mesozoic Era events: Reptiles, birds, mammals thrived Ended with a mass extinction (dinosaurs became extinct) Extinction theories include impact catastrophe with climate change Cenozoic Era events: Climatic changes- Ice Ages Species still thrived

Geologic Time Scale Divisions: Era & Periods Geologic Time Scale divides Earth’s long history into units of time. Eras  Periods  Epochs ErasPeriodsEpochsDescription PrecambrianCambrian- 1 st period Earliest era Paleozoic Mesozoic CenozoicQuaternaryHolocenePresent Day OLDEST TO RECENT

Paleozoic Era: Mass extinction killed most invertebrates and amphibians Examples of Invertebrates: Trilobites, Brachiopods

Trilobites are an extinct group of arthropods with hard, jointed external skeletons, distantly related to crabs, scorpions, and insects. They are among the most familiar fossils of the Paleozoic Era, about million years ago.

Mesozoic Era: The mass extinction at the end of the era caused the dinosaurs to become extinct

Cenozoic Era: New mammals appear while other mammals became extinct Diversity of life forms increased Flowering plants became most common Humans are part of the most recent period in this era