Transcript Chapter 14: History of Life

Chapter 14: History of Life
14.1 Biogenesis
14.2 Earth’s History
14.3 The First Life Forms
Section 1: Biogenesis
Spontaneous Generation
Before the 17th century
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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
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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
1. Knew that microorganisms grew easily in food (broth)
2. Boiled clear, fresh broth until filled with steam
3. When hot, sealed it by melting glassnecks
4. 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
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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=E936D178-9D65-4CE6-886FE10C84062305&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
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
1. Little/no oxygen
2. Size and shape of prokaryotes
3. 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
1. Replicate independently
2. Contain own genetic material
3. DNA is circular like Prokaryotes