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Evolution Unit

Evolution Unit. What do scientists think it was like on Earth billions of years ago? Where conditions different than they are today? What were the first life forms?. Chapter 14 The History of Life. http://www.cosmic-art.co.uk/graphics/earlyearth.jpg.

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Evolution Unit

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  1. Evolution Unit What do scientists think it was like on Earth billions of years ago? Where conditions different than they are today? What were the first life forms? Chapter 14 The History of Life http://www.cosmic-art.co.uk/graphics/earlyearth.jpg

  2. I. Biogenesis vs Spontaneous Generation • How did Scientist prove that spontaneous generation did not occur? • Experiments by: • Francesco Redi (1626-1697) • Lazzaro Spallanzani (1729-1799) • Louis Pasteur (1822-1895)

  3. Redi’s Experiment • Most people believed maggots spontaneously generated from rotting meat. • Redi began to study maggots, & noticed the different developmental stages of flies. • Experiment- net covered meat that kept adult flies away had no maggots.Control jar- had maggots. • Result- many people no longer supported spontaneous generation.

  4. “Vital Force” & Microbes • The microscope was invented about the time Redi did his experiment. • Scientists then thought these “simple” life forms arose spontaneously from- “vital force” in the air. • Spallanzani set up an experiment to test spontaneous generation of microbes. http://www.jasa.net.au/images/peopled.htm

  5. Spallanzani’s Experiment: Broth was heated in both experimental & control flask.Immediately sealed experimental flask. • Result: No growth in sealed flask. • Spallanzani concluded that growth occurred only if microorganisms from the air contaminated it. • Opponents- said he had destroyed the “vital force”with heat.

  6. Pasteur’s Experiment • By mid- 1800’s- sp. generation debate was fierce. • Paris Academy of Science offered prize if an experiment could prove one side. • Pasteur made a “curve neck flask”- that would prevent microbes, but not air, from entering flask. • Boiled flask- no growth. If neck broken= growth. • Pasteur won the prize & ended the debate.

  7. II. Earth’s History 1. The Formation of the Earth • About 5 billion years ago, solar system was probably a swirling mass of gas & dust. • Earth formed by collisions & gravitational pull of debris? 2. Earth’s Age • Estimates of about 4 billion years old. • How did scientists come up with this since it was so long ago? • Sedimentary rock layers • Radiometric dating http://www.aerospaceweb.org/question/astronomy/q0247.shtml

  8. 3. First Organic Compounds • Early Earth’s atmosphere: Probably had an atmosphere with CO2 (similar to Venus) and compounds like ammonia( NH3) hydrogen gas (H2), water vapor (H20) and methane (CH4) “ Reducing atmosphere” • Today’s Atmosphere: Contains 21% oxygen – probably from photosynthesis. “Oxidizing Atmosphere” • Alexander Oparin(1894-1980)- hypothesis that First Simple Organic Compounds- may have been able to form in oxygen free atmosphere.

  9. Miller/Urey Experiment • By the 1950s, scientists were in “hot pursuit” of the origin of life. • What kind of environment would be needed to allow life to begin? • In 1953, Stanley L. Miller and Harold C. Urey, working at the University of Chicago, conducted an experiment that tested Oparin’s hypothesis • They took molecules which were believed to represent the major components of the early Earth's atmosphere and put them into a closed system, added “lightening” • Results: could synthesize organic compounds

  10. Gases used were: 1. methane (CH4), 2. ammonia(NH3) 3. hydrogen (H2), and water (H2O). • Ran electric current through to simulate lightning storms (believed to be common on the early earth.) • Observed that as much as 10-15% of the carbon was now in the form of organic compounds. 2% of carbon formed some of the amino acids which make proteins. http://www.chem.duke.edu/~jds/cruise_chem/Exobiology/miller.html

  11. Other theories • There is a lot of controversy about whether the early earth atmosphere was really as “reducing” (enough that amino acids could be produced) as Miller/Urey made their experiment. Probably too extreme. • Some scientists hypothesize that organic compounds could have been carried to Earth by debris from space on Meteorites ( the Earth was frequently impacted and organic compounds could have accumulated this way)

  12. How did science explain molecule to cell jump? Some ideas: Spheres of proteins organized as membrane • Microspheres Droplets which contain organic molecules • Coacervate • These do not have the properties of life.

  13. What came 1st- The cell, the DNA or the RNA? • RNA may have been first. • RNA may act as enzymes, templates, & can self- replicate. • Early cells may have been the basis for early cell genetics.

  14. The First Cells • Early Earth conditions: • little or no Oxygen available, • many organic molecules • Have some fossils that seem to be the same size & shape of bacteria • Lack direct evidence, but the list supports the idea that the first • cells were probably • ANAEROBIC • HETEROTROPHIC • PROKARYOTIC

  15. PHOTOSYNTHESIS • Some forms of life probably became photosynthetic due to competition about 3 billion years ago. (like cyanobacteria) • Oxygen, a by-product of photosynthesis was damaging to anaerobic organisms • Bonding Oxygen was probably an early function of areobic respiration. • May have taken a billion years for oxygen to reach current atmospheric levels.

  16. The First Eukaryotic Cells • Endosymbiosis- the theory that a small aerobic prokaryotic cell was engulfed by a larger anaerobic prokaryote and began to live & reproduce inside it. • Evolved into modern mitochondria, or chloroplasts & other organelles.

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