The document summarizes the major eras of geological time from the formation of the Earth 4.6 billion years ago to the present. It outlines four eras: Precambrian, Paleozoic, Mesozoic, and Cenozoic. The Precambrian era saw the earliest life forms and atmosphere. The Paleozoic era brought marine diversity and early land plants and animals. Dinosaurs dominated during the Mesozoic before an asteroid caused their extinction. The current Cenozoic era began after this mass extinction and saw the rise of mammals and modern humans.

2. The Age of the Earth 4.6 billion years old = 4,600,000,000 Image courtesy of NASA, http://en.wikipedia.org/wiki/Image:The_Earth_seen_from_Apollo_17.jpg#file

3. The earth’s 4.6 billion year history is divided into major units of time: Cenozoic Era Mesozoic Era Paleozoic Era Precambrian Time Image created by Jason Brechko for Lake George Association (Lake George, NY) http://www.lakegeorgeassociation.org/geology_facts.htm

4. 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 Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College. Image courtesy of http://www.sharkbay.wa.gov.au/tourism/what_to_see_and_do/images/stromatolites_lge.jpg

5. 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 Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College. Images courtesy of: http://discover.edventures.com/images/termlib/p/paleozoic/support.gif , http://en.wikipedia.org/wiki/Trilobites

6. 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! Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College. c Image courtesy of http://www.ig.utexas.edu/research/projects/plates/teaching_ideas.htm?PHPSESSID=def1b9

7. 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 Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College. Image courtesy of http://nascarulz.tripod.com/dinomain.html

8. 65 million years before present…. ASTEROID IMPACT! Mass extinction of ALL dinosaurs and many marine organisms End of the Mesozoic era Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College. Image courtesy of NASA: http://www.nasaexplores.com/show2_912a.php?id=01-074&gl=912

9. 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) Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College. Image courtesy of: http://www.karencarr.com/gallery_Cenozoic_arch.html

10. 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