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Life on Earth

Life on Earth. Early Earth What was Early Earth like? Scientific Theories about evolution of organic molecules Chemicals before cells Pasteur/Virchow, Oparin, Urey/Miller Biochemical studies Search for evidence. Early Earth. Origins of Universe 10-20 billion yrs old Big Bang

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Life on Earth

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  1. Life on Earth • Early Earth • What was Early Earth like? • Scientific Theories about evolution of organic molecules • Chemicals before cells • Pasteur/Virchow, Oparin, Urey/Miller • Biochemical studies • Search for evidence

  2. Early Earth • Origins of Universe • 10-20 billion yrs old • Big Bang • Expanding ever since • Some parts condensed to form Solar Systems or groups of solar systems called Galaxies • Earth about 4.5 billion yrs old: most /all of the elements we know today had formed

  3. What was Early Earth like? • Clouds of water vapour originally surrounding Earth,condensed to form oceans and seas, still HOT! • One/two large land masses – Pangaea • Volcanoes spewed ash and lava • Atmosphere: gases Hydrogen, carbon monoxide, carbon dioxide (lots), methane, ammonia, nitrogen BUT NO OXYGEN • Electrical storms and cosmic rays produced explosive energy able to penetrate THIN atmosphere • CARBON (organic) compounds managed to originate in this hostile environment, 4 billion yrs ago • Once biological chemicals were present, primitive cells emerged about 3.5 billion yrs ago.

  4. Scientific Theories about the evolution of organic molecules • SPONTANEOUS GENERATION: people thought life arose from non-living matter. • They ‘saw’ maggots appear in rotting meat, frogs arise from moist earth and fish from muddy water. • Not scientifically tested until 1668 – Redi demonstrated that the maggots in decaying meat came from eggs laid by flies fig 3.2.1

  5. 100yrs later- Spallanzani : microorganisms that appeared in broth came from air (but this could not EXCLUDE spontaneous generation) fig 3.2.2 • 100 yrs later 1862- Louis Pasteur convinced people that Spontaneous Generation did NOT occur fig 3.2.3

  6. Chemicals before Cells • Pasteur / Virchow and others stated that “All life comes from pre-existing life” • 1923 Oparin: ‘before living things could arise, living chemicals must be formed” • He believed gases in primitive atmosphere could be converted ito molecules of biological chemicals • NOT tested until 1950’s by Urey+ Miller

  7. Urey – Miller Experiment • Simulated conditions of early earth • and to test for biological chemicals • Fig 3.2.4 • Set up apparatus containing gases- hydrogen, methane, ammonia and water vapour. • Gases were circulated between lower chamber of water (‘oceans’) and upper chamber (‘atmosphere’) • Electrical discharge passed through atmosphere chamber to simulate energy in early atmosphere • Samples withdrawn from fluid and atmosphere chambers contained amino acids and other organic molecules!!

  8. Further experiments: used UV light instead of electricity and this produced nitrogenous bases, ribose, nucleotides and amino acids. • It did NOT prove conclusively however, the origin of life but DID prove it was possible for non-living matter to produce living matter and this Chemosynthetic Origin of Life is believed by most biologists today.

  9. Chemicals from Outer Space • NO concrete evidence that chemicals came from outer space • However, carbon has been detected on other planets, meteorites and comets and floating freely in giant space clouds. • Meteorites found on Earth contain organic chemicals such as Amino acids and what appears to be fossils.

  10. Significance of Chemosynthetic and Outer Space theories • Universe began • protons, neutrons + electrons + hydrogen present • specific conditions (heat and pressure) • other elements formed • simple compounds form

  11. Biochemical Studies • All living organisms contain same type of basic chemicals eg Amino acids and sugars • Most elements and many simple compounds: hydrogen sulfide, ammonia, methane, water – existed for 6 billion yrs at least but NO biological chemicals • Nonliving (early compounds) before biological compounds (chemosynthetic theory) or came from Outer space as ready made cells???

  12. Search for Evidence • Most experiments try to replicate evolution of chemicals (Urey-Miller) • Search Outer space for more living matter • All scientists agree that for living matter to evolve, the chemicals of life must be present first for them to then become organised into cells. • Evolution from a cellular state to present day life forms took long periods of time therefore chemicals must have evolved before first cells appeared

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