Evolution introduction


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Evolution introduction

  1. 1. Biogenesis vs. Spontaneous Generation Earth’s History
  2. 2. Biogenesis vs. Spontaneous Generation Definition: All living  Definition: Living things (biotic) things come can arise (come from other living things. from)nonliving (abiotic) Common sense today, things. not believed in the 17th  Observations that century. supported the belief: Experiments conducted Maggots appeared on to prove biogenesis. rotting meat, fish appeared in seasonal ponds.
  3. 3. Francesco Redi - 1668 Addressed maggots appearing on meat. Initial observation: Maggots appear on meat after flies have landed. Hypothesis: Maggots come from flies NOT meat. Experiment: Placed meat in an open jar and in a jar that was covered with cheese cloth. Control Group Experimental Group
  4. 4. More Proof Needed… Microscope was invented around same time as Redi’s experiment. Scientists began observing ‘tiny creatures’. Accepted Redi’s conclusion but not for microscopic organisms. Believed microorganisms arise spontaneously from a “vital force” in the air.
  5. 5. Lazzaro Spallanzani(1729 -1799) Initial observation: Microorganisms grow easily in food. Hypothesis: Microorganisms formed not from air but from other microorganisms. Experiment: Placed broth in two flasks, boiled broth, one flask left open, the other sealed closed. Control Group: Experimental Group:
  6. 6. Still not convinced….. Spallanzani concluded that the boiled broth became contaminated only when microorganisms from the air entered the flask. Opponents objected to his method and disregarded his conclusion. Opponents claimed that Spallanzani had heated the flasks too long and destroyed the “vital force” in the air inside the flasks. Belief in spontaneous generation continued for another 100 years. Until………
  7. 7. Controversy grows Fierce! By mid-1800’s the arguments over S.G. were fierce. Paris Academy of Science offered a prize (equivalent to $1 million today) to anyone who could clear up the issue once and for all. The winner: Louis Pasteur. Why is that name familiar to you?
  8. 8. Pasteur’s Experiment Observations and hypothesis were the same as Spallanzani’s. To answer the objections to Spallanzani’s experiment, Pasteur made a curve-necked flask. Air from outside can mix with inside. Curve in the neck prevented solid particles, such as microorganisms, from entering the body of the flask with the broth. Finally, BIOGENESIS became a cornerstone of biology.
  9. 9. Earth’s History
  10. 10. Formation of Earth Earth is believed to be 4.56 billion years old. Earth took 400 million years to form from gas, dust and debris circling the sun. Earth grew as it was bombarded with debris. Each collision released enough energy to melt the surface of the forming planet. Estimates of Earth’s age made from studying layers of sediment in the crust. Accurate estimate through radioactive dating.
  11. 11. Radioactive (Radiometric) Dating Isotopes: atoms of the same element (same atomic number or number of protons) but differ in number of neutrons. Mass number = protons + neutrons Is0topes are designated by chemical name followed by their mass number. Example: carbon -12 and carbon- 14. Radioactive Decay: isotopes with unstable nuclei (protons and neutrons in center) tend to release particles or radiate energy (decay)
  12. 12. Radioactive Dating cont. Rates of decay of many radioactive isotopes have been determined. Half-life: the length of time it takes for ½ of any size sample of an isotope to decay. Can range from fraction of a second to billions of years but is specific to each isotope. Age of material is determined by measuring amount of a particular radioactive isotope it contains and comparing it to the amount of some other substance in the sample that remains constant.
  13. 13. Radioactive Dating cont. http://science.discovery.com/videos/100-greatest- discoveries-shorts-radiometric-dating.html If the history of the earth were condensed to a 24 hour clock, how long have humans been on the planet?
  14. 14. First Organic Compounds All elements found in organic compounds are thought to have existed on Earth and in the rest of the Solar System when Earth formed. How and where did these elements assemble into organic compounds found in life? Oparin hypothesized in 1923, Urey and Miller experimented in 1953 to test Oparin’s hypothesis. http://science.discovery.com/videos/100-greatest- discoveries-shorts-origin-of-life.html
  15. 15. The first cells. Little to no oxygen gas when they first arose so……. The first cells were anaerobic. Small size of the oldest microfossils indicate the first cells were prokaryotes (no nucleus). First cells were heterotrophs, consuming organic molecules from their environment. Autotrophs evolved due to strong pressure in the environment (competition for food). First autotrophs performed chemosynthesis.
  16. 16. Photosynthesis and AerobicRespiration Photosynthesizing autotrophs evolved and put oxygen into the atmosphere (around 3.5 billion years ago). Took billions of years for oxygen gas to reach today’s levels. Oxygen was dangerous to many early organisms because it could destroy coenzymes essential to cell function. Oxygen bonded to other compounds in some organisms, preventing damage, this was the first step to aerobic respiration.
  17. 17. The first eukaryotes. 2 to 1.5 billion years ago. Small aerobic prokaryote entered and began to live and reproduce inside larger, anaerobic prokaryotes. Mutually beneficial relationship – endosymbiosis Small aerobic prokaryote = today’s mitochondria (remember they have their own DNA) Similar situation for chloroplast in photosynthetic cells. http://videos.howstuffworks.com/discovery/29535- assignment-discovery-prokaryotes-the-first-cells- video.htm