Chapter 14: History of Life 14.1 Biogenesis 14.2 Earth’s History 14.3 The First Life Forms

Spontaneous Generation Section 1: Biogenesis Spontaneous Generation Before the 17th century Living things could arise from nonliving things Maggots appeared on rotting meat Fish appeared in ponds that had been dry the previous season 3 Experiments to disclaim spontaneous generation Redi’s Experiment Spallanzani’s Experiment Pasteur’s Experiment

Redi’s Experiment Francesco Redi (1626-1697), Italian Studied flies development Observed: 1) tiny wormlike maggots turned into oval cases and then flies 2) maggots appeared where adult flies had landed Experiment: 1) Open jar with meat inside 2) Closed jar with meat inside 3) Netting-covered jar with meat inside

Concluded: flies come from eggs laid by other flies **major blow against spontaneous generation

Spallanzani’s Experiment Lazzaro Spallanzani (1729-1799), Italian Designed experiment to test spont. gen Hypothesis: Organisms formed not from air, but from other microorganisms Knew that microorganisms grew easily in food (broth) Boiled clear, fresh broth until filled with steam When hot, sealed it by melting glassnecks Remained clear and free of microorg, while the control became cloudy (Some believed that the boiling of the broth and the sealing of the flask had somehow altered the air so as to prevent spontaneous generation from occurring)

Pasteur’s Experiment Louis Pasteur (1822-1895), French Improved Spallanzani’s experimenet Used a curved-necked flask allowed the air inside to mix with air outside Curve prevented solid particles from entering the body of the flask

Biogenesis Following these experiments, people no longer believed in spontaneous generation Biogenesis: all living things come from other living things Became a cornerstone in biology

Section 2: Earth’s History Formation of the Earth In light of biogenesis, how did cell-based life arise in the first place? Any theories out there?

Computer models of sun suggest: 5 billion years ago (bya) our solar system was a swirling mass of gas and dust Over time, material pulled by gravity and formed the sun Remaining gas/debris circled Planets formed through repeated collisions of space debris

EARTH Estimated age: 4.5 billion years Studied layers of sedimentary rock in Earth’s crust Used radiometric dating Decay of uranium and thorium isotopes in rock crystals Oldest rock crystals are ~4by Bill Nye http://player.discoveryeducation.com/index.cfm?guidAssetId=E936D178-9D65-4CE6-886F-E10C84062305&blnFromSearch=1&productcode=US

Lab Radioactive Dating or Visual Concepts CD

Early Atmosphere Hypotheses Oparin and Haldane (1920’s) NH3, H2, H20 vapor, CH4 At high temps, these gases may form simple organic compounds Amino acids Earth cools, water vapor condenses, o-compounds collect in the water Over time, with chemical rxns (fueled by lightning or UV radiation) turned into proteins

Americans Miller (1930) and Urey (1893-1981) Performed experiment Produced variety of organic compounds including amino acids Others replicated and found: ATP, nucleotides, etc)

Another hypothesis Atmosphere was mostly CO2, N2 and H2O vapor Experiments CO2 and O2 interfere with production of organic compounds Concluded Production only in protected areas… undersea hot springs

Another Organic compounds could have been carried by debris from space 1970 broad mix of organic compounds found on newly fallen meteorite.

Cell-like structures Sidney Fox (1912-1998) Microspheres: spherical, composed of many protein molecules organized as a membrane Coacervates: droplets that are composed of molecules of different types, including lipids, amino acids and sugars

Connection to life? Both can form spontaneously under certain conditions Some cell-like properties: ability to take up certain substances, grow, can bud Hypothesizing how living cells may have formed from simpler ingredients

RNA World Model Thomas Cech (1947-) Section 3: The First Life Forms RNA World Model Thomas Cech (1947-) Ribozyme: type of RNA in some unicellular Eukaryotes can act like an enzyme Act as a catalysts in their own replication Perhaps first case of heredity (and competition)

First cells Inferences Little/no oxygen Size and shape of prokaryotes Lived in environment filled with organic molecules as food 1st cells probably anaerobic, heterotrophic prokaryotes Stromatolites

Archaea Group of unicellular organisms Live in extremely harsh environments Energy: chemosynthesis CO2

Yellowstone National Park

Photosynthesis Forms of life became photosynthetic 3 bya Oldest known fossils similar to modern cyanobacteria Billions of years for O2 to reach atmosphere ozone

Eukaryotes Lynn Margulis: Endosymbiosis Eukaryotes evolved from a mutualistic beneficial relationship between primitive eukaryote and the prokaryote it engulfed Aerobic prokaryotes engulfed gave rise to mitochondria Photosynthetic cyanobacteria engulfed gave rise to chloroplasts

Evidence Mitochondria/Chloroplasts Replicate independently Contain own genetic material DNA is circular like Prokaryotes