1. History of Life on Earth

2. Objectives Summarize how radioisotopes can be used to determine the age of the earth Compare two models that describe how the chemicals of life originated Describe how cellular organization might have begun

3. Age of the Earth Scientist believe that the earth originated 4.5 billion years ago They speculate that it was a fiery ball of molten rock that cooled into a solid rock Water vapor in the atmosphere condensed to form the vast oceans of the planet Most scientists believe that life began in these oceans

4. Radiometric Dating Radiometric Dating: A process of measuring the age of an object by determining its concentration of certain radioactive isotopes Scientists estimate the age of the earth through a process called radiometric dating

5. Law of Superposition A general law stating that in any sequence of sediments or rocks that has not been overturned, the youngest sediments or rocks are at the top of the sequence and the oldest are at the bottom

6. Half-Life The time it takes for one- half of a given amount of radioisotopes to decay By measuring the proportions of certain radioisotopes and their decay, scientists can compute how many half- lives have passed since a rock was formed

7. Formation of Chemical Life Scientist believe that life began as a random series of chemical and physical processes. It is thought that life began when non-living chemicals reacted chemically during the first billion years of the earth's history

8. Primordial Soup Model Scientists A.I. Oparin and J.B.S. Haldane Suggests that the ocean was filled with many different organic molecules Theorized that molecules spontaneously formed in chemical reactions powered by lightening, volcanoes and solar radiation

9. Urey-Miller Model 1953 Stanley Miller tests Primordial Soup theory He created complex organic molecules using the basic gases found in the earth's ocean

10. However... It was later determined that the earth did not posses an ozone layer. The ozone layer protects the earth from the sun's ultraviolet rays Without the layer of protection the rays would have destroyed any complex molecules created by the primordial soup model

11. Bubble Model If gases necessary for life to evolved had not existed in the atmosphere, where did they come from? 1986 Louis Lerman suggested that the gases were trapped in bubbles on the surface of the ocean

12. Bubble Model Simple organic molecules from number eruptions of undersea volcanoes were trapped in bubbles Inside the bubbles gases underwent chemical reactions due to the concentration of the chemicals

13. Bubble Model Bubbles rose to the surface and burst releasing the organic molecules into the air Up in the air, the organic molecules were exposed to ultraviolet radiation and lightening which provided energy for more reactions

14. Bubble Model More complex organic molecules formed by further reactions fell into the ocean with rain, starting another cycle