Geologic-Time-Scale. SCIENCE 11 SEMESTER 1
- 2. The Precambrian (4,600 to 540 Ma)
- 3. •Represents 80% of Earth’s history •Eon of “Hidden Life” – fossil record obscure. Precambrian
- 4. •From “Haedes” Greek god of the underworld •Chaotic time, lots of meteorite bombardment •Atmosphere reducing (Methane, Ammonia, CO2) •Start of the hydrologic cycle and the formation of the world oceans •Life emerged in this “hostile” environment Hadean Eon (4,600 – 3,800 Ma)
- 5. •Anaerobic (lack of oxygen) •No Ozone •Photosynthetic prokaryotes (blue green algae) emerged and started releasing oxygen to the atmosphere •Life forms still limited to single celled organisms without a nucleus (prokaryotes) until 2,700 Ma when Eukaryotes emerged. Archean Eon (3,800 – 2,500 Ma)
- 6. •Oxygen level reaches ~ 3% of the atmosphere •Rise of multicellular organisms represented by the Vendian (Ediacaran) Fauna •Formation of the protective Ozone Layer Proterozoic Eon (2,500 to 540 Ma)
- 7. Phanerozoic Eon (540 Ma to Present)
- 8. •Eon of “visible life” •Diversification of life. Many life forms represented in the fossil record •Life forms with preservable hard parts Phanerozoic
- 9. •Age of “Ancient Life” •Rapid diversification of life as represented by the Cambrian Fauna (Cambrian Explosion) •Dominance of marine invertebrates •Plants colonize land by 480 ma Paleozoic Era (540 – 245 Ma)
- 10. •Animals colonize land by 450 ma •First insects and arthropods •Oxygen level in the Atmosphere approaches present day concentration •Massive Extinction at the end (End of Permian Extinction)
- 11. •Age of Reptiles •Dominance of reptiles and dinosaurs •Pangea starts to break-apart by 200 ma •Early mammals (220 ma) •First birds (150 ma) Mesozoic Era (245 – 65 Ma)
- 12. •First flowering plants (130 ma) •Mass Extinction at the end of the Cretaceous (65 ma)
- 13. •Age of Mammals •Radiation of modern birds •Early Primates 60 ma •Continents near present-day positions (40 ma) •First hominids (5.2 ma) Cenozoic Era (65 Ma to present)
- 14. •Modern humans (0.2 ma) •Global ice ages begin (2 Ma)
- 15. •End Ordovician – 25% of marine vertebrates families and 57% of genera became extinct (443 ma) •Devonian – 50 -55% of marine invertebrate genera and 70-80 % of species go extinct (364 ma) •Permian – greatest extinction event; 90% of all species became extinct (250 ma) Extinctions
- 16. •End Cretaceous – extinction of the Dinosaurs; 60-80% of all species became extinct (65 ma) •Late Pleistocene – nearly all large mammals and birds (>45 pounds) became extinct (.01 ma) Extinctions