Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Chapter 17The History of Life1How Did Life Begin??People used to believe that new organisms sprang up all of the time through spontaneous generation•Microorganisms from broth•Maggots from meat•Mice from sweaty clothes and wheatExperiments disproved spontaneous generation217.1Fig E1.13417.1Louis PasteurPasteur also performed expermients that refuted spontaneous generationFig 17.1517.1How Did Life Begin??The first living things must have come from nonliving materialsWe know that organic molecules can form spontaneously under low oxygen conditionsThis has been experimentally supported617.1Fig 17.27How Did Life Begin??The first living things must have come from nonliving material•Some RNA molecules, called ribozymes, can catalyze reactions•Membrane-like vesicles may have enclosed ribozymes forming protocellsBut there is no real evidence as to how life began17.18Early EarthEarth is 4.5 billion years oldEarly Earth was thought to be very hot with a lot of volcanic activity and electrical stormsEarly earths atmosphere lacked oxygen gasFig 17.417.2917.2Life Began During the Precambrian EraThe oldest fossil organisms found so far are about 3.5 billion years old1017.2Early LifeSome organisms evolved the ability to capture energy from sunlight while using the earths most abundant source of hydrogen – water (H2O)Photosthesis increased the amount of oxygen in the atmosphere6CO2+6H2O+light energy>C6H12O6 +6O211Early LifeNewly liberated oxygen gas was quickly consumed by reactions with other moleculesOne common reactive atom in the earths crust was iron•There are large iron oxide (rust) deposits in rocks from this period17.212Early LifeOnce most of the iron had turned to rust oxygen began to accumulate in the atmosphereChemical analysis of rocks suggests significant amounts of oxygen first appeared in the atmosphere about 2.3 billion years agoOxygen is potentially dangerous to living things•Many anaerobic organisms are killed by oxygen•It reacts with and breaks down organic molecules17.213Early LifeAerobic metabolism evolved in response to the increased oxygen levels•Provides defense against the chemical action of oxygen•Also channels oxygen to make useful energyCells that could utilize aerobic respiration had a significant advantage over cells that do not17.214The Evolution of EukaryotesSome organisms acquired membrane enclosed organellesEukaryotes could have evolved through a combination of two processes•Inward folding of the plasma membrane•The endosymbiont hypothesis17.215The Evolution of EukaryotesInward folding of the plasma membrane•Membrane infolding of near DNA could have formed precursors to nuclei•Infoldings could also have formed ER and Golgi structures17.216The Evolution of EukaryotesThe endosymbiont hypothesis•Mitochondria and chloroplasts may have arisen from engulfed photosynthetic bacteriaHow could this happen?•Mitochondria – a predatory anaerobic cell could have captured an aerobic bacterium for food but failed to digest•Chloroplast – some of these predatory cells could also have captured photosynthetic bacterium17.217The endosymbiont hypothesis17.2Fig 17.51817.2Evidence for the endosymbiont hypothesisThere are many distinctive similarities between eukaryotic organelles and living bacteriaMitochondria and chloroplasts each contain their own DNAThe presence of living intermediates• Ex: Paramecium harbor a photosynthetic algae1917.2Evidence for the endosymbiont hypothesisThe presence of living intermediatesEx: Paramecium harborPhotosynthetic algaeFig 17.620The Evolution of Eukaryotes: Summary17.221Evolution of multicellular organismsPredation provided selective pressure that favored large size•Large cells are harder to engulf and digest•Larger organisms are usually fasterBut there is a limitation on cell size•Back to chapter 5, page 91 17.322The ability to exchange materials across the plasma membrane limits cell sizeA large cell will haveA relatively smallSurface area throughWhich to obtain Nutrients and Eliminate wasteFig 5.1617.32317.3Evolution of multicellular organismsThere are only two ways an organism larger than about one millimeter in diameter can survive1. Possess a low metabolic rate•Requires less oxygen•Produce little carbon dioxide2. Be multicellular•Consist of many small cells packaged into a larger unified bodyThe oldest multicellular fossils are about 1.2 billionyears old2417.4How did life invade land?There were many obstacles to overcome in order for an organism to leave the sea and inhabit dry landBenefits of life in the water include:•Protection from gravity•Ready access to water•Sperm and/or eggs can swim or drift to one another25How did life invade land?Inhabiting land was very advantageous (esp for plants)•Unobstructed sunlight (water absorbs light)•Abundance of nutrients lacking in the sea•Particularly nitrogen and phosphorus•There were no organisms on land that ate plantsSoon after plants invaded land animals followedFig 17.917.42617.5What role has extinction played in the history of life?Evolutionary history has been marked by periodic mass extinctions• the relatively sudden disappearance of a wide variety of species over a large part of the earthMass extinctions have separated many series of evolutionary dynasties•Where one dominant group rules the land of sea for a period of time27Mass Extinctions• Indicated by asterisks17.5 Fig 17.112817.5What Can Cause Mass Extinctions?Climate change•One cause of climate change is the shifting positions of continents – continental driftCatastrophic events•Massive volcanic eruptions•Impact of a huge meteorite29Continental drift is caused by plate tectonicsSource: NASA17.530Continental drift is caused by plate tectonics17.5Fig 17.12a3117.5Continental drift is caused by plate tectonicsFig 17.12d3217.5Continental drift is caused by plate tectonicsThe effects of plate tectonics continues to be seen todayEx: the Atlantic Ocean widens by a few centimeters each year3317.5Was the extinction of the dinosaurs caused by the impact of a huge meteorite?65 million years ago there was a giant meteorite strike and a mass extinction eventChicxulub crater •100 mile wide crater buried beneath the
View Full Document
Unlocking...