Earth History: Geologic Time

Geologic Time Geologic Time: It is very, very long. Earth is estimated to be around 4.7 billion years old based on the rock and fossil record. Geologic time is broken up into sections based on major changes in Earth .

Divisions of Geologic Time Largest Division: Eons Eons divided into Eras: PreCambrian, Paleozoic, Mesozoic, Cenozoic Ceno - recent Meso - middle Paleo - ancient Zoic - life Eras are divided into Periods

PreCambrian 543 million years ago to ~ 4 billion years ago (?) “Age of Bacteria” Oldest Era Longest era because we know so little about the earth that long ago Life: Very little life: only basic forms including bacteria, the oldest fossils ever found, seaweed, jellyfish, and worms Photosynthesis of the seaweed added oxygen to the early atmosphere, paving the way for land life.

First Life One celled plants (algae) entered the fossil record approximately 3 b.y. ago (Precambrian). Large colonies of this algae are called stromatolites.

More Atmospheric Changes Through photosynthesis, O2 was released into the atmosphere and ocean allowing animals to eventually evolve.

Paleozoic 543 million years ago to 248 million years ago “Age of the Fish” Explosion of life in the sea: trilobites, shellfish, Fish Life appears on land: Ferns, Amphibians Pangaea formed Largest mass extinction ever at the end of the Paleozoic. 90% of species became extinct.

Paleozoic Organisms

Carboniferous Time In Europe the Mississippian and Pennsylvanian periods are together called the Carboniferous period. Vast swamps and forests from that time created the huge coal beds found throughout eastern United States.

Mesozoic 248 mya- 65mya “Age of the Reptiles” Life: Reptiles are the dominant life on land. Dinosaurs exist. Birds appear. Forests of trees appear Pangea broke apart during this peroid. Dinosaurs become extinct in a mass extinction at the end of the Mesozoic.

Reptiles: …until Dinosaurs took over. Appeared in the Permian and quickly became the dominant life form. Reptiles: …until Dinosaurs took over. They ruled the planet throughout the Mesozoic era (the “Age of Dinosaurs”).

Birds Archaeopteryx is the oldest fossil bird found to date. Some of the dinosaurs are thought to have evolved into birds. Archaeopteryx is the oldest fossil bird found to date.

2. Meteorite impact causes multiple natural disasters Dinosaur Extinction 2. Meteorite impact causes multiple natural disasters 1. Volcanoes erupt and fill the atmosphere with CO2 and gasses that BLOCK the sun light preventing plant life…….

Evidence of a Meteorite Layer of Iridium in rock layers

Cenozoic 65 mya- present “Age of the Mammals” Life: Large mammals appear, Humans appear Ice Ages occur and ice sheets advance

Mammals The Cenozoic is the “Age of Mammals”. Mammals first appeared in the Mesozoic as small rodents. After the dinosaurs were erased at the end of the Mesozoic, Mammals quickly evolved to become the dominant life form. The Cenozoic is the “Age of Mammals”.

Present We live in the Holocene epoch, of the Quaternary period, of the Cenozoic era.