Earth History - The Geologic Time Scale

The Age of the Earth 4.6 billion years old = 4,600,000,000

The earth’s 4.6 billion year history is divided into major units of time: Precambrian Time Paleozoic Era Mesozoic Era Cenozoic Era

Precambrian Time 4.6 billion years before present to 544 million years before present Longest era with a sparse fossil record Origin of earth’s crust, first atmosphere, and first seas Earliest fossils of cyanobacteria use photosynthesis to produce oxygen Ozone layer in the atmosphere is formed from oxygen

Paleozoic era 544 million years before present to 245 million years before present Marine communities flourish Early fishes develop Origin of amphibians, insects & reptiles Recurring ice ages/ Appalachians mountains form Spore-bearing plants dominate .

Paleozoic era (continued)… 286 - 248 million years before present: Supercontinent of Pangea forms 248 million years before present: MASS EXTINCTION-90 % of all known families lost! c .

Mesozoic Era 245 million years before present - 65 million years before present The age of the dinosaurs! Gymnosperms dominate land plant/ origin of angiosperms - flowering plants Origin of mammals & birds 145 million years before present - asteroid impact? MASS EXTINCTION Pangea begins to separate/ Rocky mountains form

65 million years before present…. ASTEROID IMPACT! Mass extinction of ALL dinosaurs and many marine organisms End of the Mesozoic era .

Cenozoic Era 65 million years before present - today Present era we live in Continued evolution and adaptations of flowering plants, insects, birds, mammals Mammals dominant Major crustal movements & mountain building (Alps & Himalayan mountains form) .

And during the Cenozoic era… The most primitive hominid (human ancestor) evolves - approximately 4.4million years before present The first modern humans (homo sapiens) evolved approximately 100,000 years before present Image courtesy of: http://www.wilderdom.com/images/evolution/8.jpg

Assignment – You can use your Textbook and your cell Phones Describe the Experiments of Louis Pasteur and Alexander Oparin and Stanley Miller in relation to Formation of First Cells on Earth. Bacteria were the first living cells on earth. How did Eukaryotic or Multicellular organisms came into being. Describe Endosymbiosis.