Where does life come from? Spontaneous generation the belief that living things arise from nonliving things Biogenesis all living things come from other living things Redi’s experiments Spallanzani’s experiments Pasteur’s experiments
Redi’s Experiment (1626-1697) Italian physician and poet who demonstrated that the presence of maggots on rotting meat does not result from spontaneous generation but from eggs laid on the meat by flies. maggotsspontaneous generation Pg. 279
Spallanzani’s Experiments (1729-1799) Italian naturalist whose experiments disproved that microorganisms spontaneously generated from meat broth in open flasks. Pg. 280
Pasteur’s Experiment (1822-1895) A French chemist who proved that microorganisms are carried by dust and not air. Improved on Spallanzani’s experiment Pg. 281
The First Organic Compounds Alexander Oparin’s Hypothesis, 1920’s): Thought that primitive atmosphere contained: NH 3, H 2, H 2 0, and C-H compounds At high temperatures, these gases might have formed simple organic compounds like amino acids
Oparin’s Theory Con’t When the Earth cooled, the water vapor condensed into lakes and seas with the organic compounds within With the help of lightening and UV radiation, these organic compounds reacted with each other forming macromolecules essential to life.
Can that REALLY happen? Yes! According to experiments performed by Miller and Urey Products of experimental synthesis: Amino acids ATP DNA nucleotides
Miller Experiment Water Vapor Forms Input Chamber Condenser Spark Chamber Attempts to Create Life
Life began in Hydrothermal Vents Extreme conditions: high heat, acid levels, pressure, gases Sun cannot reach the bottom of the ocean Chemosynthesis- organisms making their own energy from the chemicals in their enviro. (similar to photosynthesis) Currently populated by Archae
Vents cont. Scientists have also traced the DNA of all currently living organisms back to a common ancestor extremophile that would have been found in the hydrothermal vents.
“It came from outer space!” Some scientists hypothesize that organic compounds may have come from meteoroids from space
Earth’s Age More than 4 BILLION years old! How do scientists “know” this? Radiometric dating Measurement of the decay of commonly occurring radioactive isotopes Ex) Carbon dating
Fossils The remains of ancient animals and plants Found in every continent on earth Formed from sedimentary rock Paleontology- the branch of biology that studies past forms of life (namely fossils!)
The Fossil Record From the 1830s onwards, geologists noted how fossils became more complex through time. The oldest rocks contained no fossils, then came simple sea creatures, then more complex ones like fishes, then came life on land, then reptiles, then mammals, and finally humans. Clearly, there was some kind of 'progress' going on.
The First Prokaryotes About 3.5 bya the first prokaryotes, cells without a true nucleus (like bacteria), came into existence. The first cells were probably anaerobic and heterotrophic. Video
Prokaryotes cont. Resemble modern day Archaebacteria, which live in extreme environments Chemosynthesis- the conversion of carbon molecules (like CO2 or methane) into organic compounds without the use of sunlight energy is obtained from an inorganic substance like sulfur, hydrogen gas, or methane
Rise of photosynthesis and aerobic respiration Cyanobacteria- group of unicellular, autotrophic prokaryotes about 3 bya Increased the level of atmospheric oxygen
The First Eukaryotes Endosymbiosis- about 2.0 bya, a small aerobic prokaryote began to live inside a larger anaerobic prokaryote aerobic prokaryotes evolved to modern mitochondria Photosynthetic cyanobacteria evolved into chloroplasts video
Endosymbiosis: From prokaryotes to eukaryotesFrom prokaryotes to eukaryotes
Ch. 14 Notebook Quiz 1. What does the term biogenesis mean? 2. Explain how Redi’s experiment disproved the hypothesis that flies formed by spontaneous generation. 3. What is the Earth’s age? How do we know this? 4. According to Oparin, what molecules were in Earth’s early atmosphere? 5. What process increased the level of oxygen in the atmosphere about 3 bya? 6. Explain the theory of endosymbiosis.