The History of Life

1. The History of Life Chapter 14

2. Early Earth • Was inhospitable! • Very hot due to: • Meteoric impact • Volcanic eruptions • Radioactive decay • Early atmosphere contained: • Mostly water vapor, nitrogen, and carbon dioxide • Almost no oxygen.

3. Early Earth Timeline • ~4.6 bya: Formation of the Earth • ~4.5 bya: Formation of the moon • ~4.0 bya: Earth begins to cool • ~3.9 bya: • Oldest rocks • Primordial oceans begin to form • ~3.8 bya: First prokaryotic organisms • ~2.5 bya: First stable continents • ~2.1 bya: First eukaryotic organisms

4. Fossils • Over 99% of the organisms that have ever lived on this Earth are now extinct!! • We know about these organisms by impressions left in rocks, amber and ice.

5. Dating Techniques • Relative Dating • Places items in sequence • No exact date is assigned • Numeric Dating • Provides an actual date • Radioactive Dating: utilizes radioactive isotopes of elements.

6. Geologic Time Scale

7. Early Theories on the Origin of Life • Spontaneous Generation • Idea that nonliving material can produce life • Biogenesis • Idea that living organisms must come from other living organisms.

8. Spontaneous Generation • Italian scientist, Francisco Redi, disproved the myth, but only for larger organisms. • But scientists still believed that maybe microorganisms arose spontaneously from the air. • French scientist, Louis Pasteur, finally disproved spontaneous generation by designing an experiment where air but no organisms were allowed to contact a nutrient broth…nothing grew!

9. Francesco Redi’s Experiment

10. Pasteur’s Experiment

11. Modern Theories • Two developments must have preceded life on Earth • Formation of organic (carbon-containing) molecules • Formation of protocells (early cells)

12. Formation of Organic Molecules • Simple organic molecules (carbon containing) must have formed • These molecules must have organized into more complex molecules like proteins, carbohydrates, lipids and nucleic acids. • In 1930, Russian scientist, Alexander Oparin, hypothesized life began in oceans by chemical reactions with the atmosphere, lightning, and Earth’s heat to produce organic molecules.

13. Primordial Soup Theory • Developed by Alexander Oparin. • Earth’s ancient atmosphere probably contained nitrogen, methane, and ammonia gases, but little to no oxygen. • Energy from sun fueled chemical reactions in the atmosphere forming organic molecules (Carbon based molecules) like amino acids • These molecules were then washed into the oceans making a primordial soup of organic molecules • Eventually these proteins, lipids, and other organic molecules formed the first cells.

14. Miller and Urey’s Experiment • In 1953, American scientists, Stanley Miller and Harold Urey tested Oparin’s hypothesis. • Their result was the formation of amino acids, sugars and other simple organic molecules. • This supportedOparin’s hypothesis.

15. Formation of Protocells • Various experiments during the 1950’s showed how complex organic molecules might have formed from small organic molecules in pools of heated water. • American scientist, Sidney Fox, provided a mechanism to explain the formation of protocells. • A protocell is a large, ordered structure, enclosed by a membrane, that carries out some life activities such as growth and division.

16. Evolution of the Cell • First cells were prokaryotes that may have evolved from protocells. • They were anaerobic organisms, meaning they lived in the absence of oxygen. • They were also heterotrophs, meaning they obtained food rather than making it themselves.

17. First Autotrophs • Auto means self ; troph means energy • Were probably similar to today’s archaebacteria: prokaryotic chemosynthetic organisms found in harsh conditions such as deep sea vents. • Chemosynthesis is the process of releasing energy from inorganic compounds such as H2S.

18. First Photosynthetic Organisms • Are responsible for the first atmospheric oxygen. • Were also prokaryotes. • Also responsible for the ozone layer. • The ozone layer provided protection against high energy radiation such as UV and gamma rays. • This allowed organisms to move on to land. • This allowed for more aerobic organisms.

19. Endosymbiont Theory • Proposed in the 1960’s by American biologist, Lynn Margulis. • Explains how eukaryotic cells may have arisen. • States that: • Mitochondria and chloroplasts were actually once prokaryotic cells. (They both have their own DNA similar to prokaryotic DNA.) • A cell ingested these bacteria and the bacteria were protected while providing energy for the cell. Eventually the bacteria could no longer live on their own, and the eukaryotic cell evolved.

20. Different View Points • Divine Origins – some cultures believe that life did not arise spontaneously but that it was placed here by a creator. • Meteorites – theory that life arrived here on meteorites. • Bubbles – In 1986, Louis Lerman proposed that the chemical reaction in the primordial soup took place inside tiny lipid bubbles • RNA first? – Other scientists propose that self replicating molecules came before the cell. They proposed that RNA came before DNA.