1. Fossil Evidence of Change Land Environments The History of Life Section 1  Earth formed about 4.6 billion years ago.  Gravity pulled the densest elements to the center of the planet.  The planet began to cool after about 500 million years.  A solid crust formed on the surface.  Water vapor condensed and formed the oceans.  Most scientists believe life began in the oceans

2. Fossil Evidence of Change Atmosphere The History of Life  The gases that likely made up the atmosphere are those that were expelled by volcanoes.  Water vapor, Carbon dioxide, Sulfur dioxide, Carbon monoxide, Hydrogen sulfide, Hydrogen cyanide, Nitrogen, and Hydrogen  NO Oxygen (O 2 ) Section 1

3.  Uses the decay of radioactive isotopes to measure the age of a rock  Radioactive dating is the method used to determine the age of the earth and of fossils. Radiometric Dating The History of Life Fossil Evidence of Change Section 1

4. Clues in Rocks The History of Life  A fossil is any preserved evidence of an organism.  Examples of fossils include bones, shells, and impressions of dead organisms left in rocks.  Most organisms decompose before they have a chance to become fossilized. Fossil Evidence of Change Section 1

5. Fossil Formation The History of Life  Nearly all fossils are formed in sedimentary rock.  The sediments build up until they cover the organism’s remains.  Minerals replace the organic matter or fill the empty pore spaces of the organism. Fossil Evidence of Change Section 1

6. Dating fossils The History of Life  Relative dating is a method used to determine the age of rocks by comparing them with those in other layers. Fossil Evidence of Change Section 1

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8.  Plate tectonics describes the movement of several large plates that make up the surface of Earth.  These plates, some of which contain continents, move atop a partially molten layer of rock underneath them. The History of Life Fossil Evidence of Change Section 1

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10. The Origin of Life Origins: Early Ideas The History of Life  Spontaneous generation is the idea that life arises from nonlife.  Francesco Redi, an Italian scientist, disproved the idea that flies arose spontaneously from rotting meat. Section 2

11.  The theory of biogenesis states that only living organisms can produce other living organisms.  Louis Pasteur designed an experiment to show that biogenesis was true even for microorganisms. The History of Life The Origin of Life Section 2

12. Simple Organic Molecule Formation The History of Life  Life may have began at the surface of the ocean where UV light from the Sun and lightning were the primary energy sources.  Many scientists believe life began at the depths of the ocean where geothermal vents provided the energy for organic molecule formation. The Origin of Life Section 2

13. The Primordial Soup Model The History of Life  In the 1920’s Oparin and Haldane both suggested that the early Earth’s oceans contained large amounts of organic molecules.  This hypothesis became known as the primordial soup model.  In 1953, the primordial soup model was tested by Miller and Urey. The Origin of Life Section 2

14.  Stanley Miller and Harold Urey were the first to show that simple organic molecules could be made from inorganic compounds.  Later, scientists found that hydrogen cyanide could be formed from even simpler molecules in simulated early Earth environments. The History of Life The Origin of Life Section 2

15. The Bubble Model The History of Life  In 1986, the geophysicist Louis Lerman suggested that the key processes that formed the chemicals needed for life took place within bubbles on the ocean’s surface. The Origin of Life Section 2

16. The Bubble Model The History of Life The Origin of Life Section 2

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18. Genetic Code The History of Life  Some RNA sequences appear to have changed very little through time.  Many biologists consider RNA to have been life’s first coding system.  Other researchers have proposed that clay crystals could have provided an initial template for RNA replication. The Origin of Life Section 2

19. Cellular Evolution The History of Life  Scientists hypothesize that the first cells were prokaryotes.  Many scientists think that modern prokaryotes called Archaea are the closest relatives of Earth’s first cells. The Origin of Life Section 2

20. Photosynthesizing Prokaryotes The History of Life  Fossil evidence of cyanobacteria has been found in rocks as old as 3.5 billion years.  Cyanobacteria eventually produced enough oxygen to support the formation of the ozone layer.  Ozone blocks the sun’s UV rays  With oxygen and the ozone layer in the atmosphere, life could migrate onto land. The Origin of Life Section 2

21. The Endosymbiotic Theory The History of Life  The ancestors of eukaryotic cells lived in association with prokaryotic cells.  It has been suggested that a large prokaryote engulfed a smaller one, which continued to live and provide energy to the larger prokaryote  The relationship between the cells became mutually beneficial, and the prokaryotic symbionts became organelles in eukaryotic cells.  This theory explains the origin of chloroplasts and mitochondria. The Origin of Life Section 2

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