1. Origins of Life

2. Earth was very different Billions of Years Ago The Earth is thought to be 4.6 Billion Years Old Early Earth was lifeless –Intensely hot molten lava –No Oxygen Eventually, rain fell and cooled the surface a little, resulting in a rocky crust and ocean formation

3. How did life emerge from “non-life”? Life developed when molecules of non- living matter reacted chemically during first billion years of Earth’s history (Spontaneous Origin) Simple Molecules  Complex Molecules by means of energy

4. Life’s Building Blocks Hydrothermal Vents –Crack in Earth’s surface under water from which very hot water escapes –Scientists think that heat from hydrothermal vents could have provided energy for chemical reactions to change molecules into organic molecules

5. Life’s Building Blocks Space –Some scientists think that organic molecules could have arrived on Earth on meteorites –Meteorites are natural objects originating in outer space that survives impact with the Earth's surface

6. Early Prokaryotes By 3.8 bya, the early seas were filled with organic molecules The jump from free-floating molecules to the first cells is unclear First prokaryotes were anaerobic – they got their E from organic molecules Photosynthetic life evolved about 3.5 bya Cyanobacteria are photosynthetic and released oxygen into atmosphere This allowed for the evolution of aerobic prokaryotes

7. Eukaryotes Evolved about 1.5 bya Hypothesis of eukaryote evolution was proposed by Lynn Margulis Theory of Endosymbiosis –When one organism lives within the body of another, and both benefit from the relationship.

8. Eukaryotes The theory suggests that mitochondria and chloroplasts once lived independently About 1.5 bya, they were engulfed by larger prokaryotic cells Instead of being consumed, bacteria began to live inside host cell where they performed photosynthesis or cellular respiration

9. The Fossil Record As said earlier, scientists hypothesize that the Earth is 4.6 billion years old Fossil evidence indicates that for much of that long history, Earth has been the home of living things The fossil record includes all the remains of living things on Earth Although the examination of the fossil record will never be complete, it presents strong evidence that evolution has taken place

10. How Fossils Form Most are found in sedimentary rock (rock that is formed by the settling of layers of sediment) This layering allows dead organisms to be preserved and fossilized

11. Where are Fossils Formed? Environments that often cause fossil formation are –wet lowlands –slow-moving streams –lakes –shallow seas –areas near volcanoes Why?

12. Fossils Aren’t Always Formed If an organism dies in an area where fossils can’t be formed, they are not formed Fossils of soft-bodied or delicate organisms are rare because they are often destroyed by the heavy sediment Even if an organism that fossilizes well dies in an area where fossils are formed, it might be eaten before it can become fossilized

13. Analyzing Fossil Evidence In order to analyze fossil evidence, paleontologists use both relative and absolute dating methods to date a fossil

14. Relative Age of Fossils Relative dating is used to estimate ages of fossils found within layers of sedimentary rock (strata) Relative Dating cannot reveal a fossil’s age in years, but it can reveal the order in which organisms lived on Earth

15. Absolute Age of Fossils Radiometric dating estimates the age in years of an object by measuring how much of a certain radioactive element is found in the rock surrounding the fossil Video

16. Describing Geologic Time The geologic time scale is based on evidence in the fossil record and has been shaped by mass extinctions (when large numbers of species become extinct) Evidence indicates that world-wide climate changes are common factors that contribute to mass extinctions

17. Present CENOZOIC ERA Age of Mammals Mass Extinction MESOZOIC ERA Age of Reptiles Mass Extinction PALEOZOIC ERA Age of Invertebrates, Land Plants, and Amphibians Past