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Chapter 17

Chapter 17. The Origin of Life. 17.1 The Big Bang. Evidence indicates that 15 billion years ago, Universe = one big supermass that exploded Explosion of the supermass – “Big Bang” – hurled matter & energy into space & then pulled together into clumps (stars, galaxies, planets, etc).

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Chapter 17

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  1. Chapter 17 The Origin of Life

  2. 17.1 The Big Bang • Evidence indicates that 15 billion years ago, Universe = one big supermass that exploded • Explosion of the supermass – “Big Bang” – hurled matter & energy into space & then pulled together into clumps (stars, galaxies, planets, etc)

  3. 17.1 The Big Bang • Age of Earth = ~ 4.6 billion years old

  4. 17.2 Early Earth • Early atmosphere = very hot, composed of volcanic gasses – nitrogen, hydrogen, carbon monoxide, carbon dioxide, & water vapor • It’s believed there was NO Oxygen

  5. 17.2 Early Earth • O2 accumulated in atmosphere ~ 2.5 billion years ago • When photosynthesizers started to produce O2 as a waste product • O2 reached modern levels about 360 million years ago

  6. 17.3 The Beginnings of Life • Reasons why Earth was hostile to living things: • Volatile (very reactive) gasses • UV radiation would have damaged DNA

  7. 17.3 The Beginnings of Life • 3 Popular scientific explanations for the origin of life: • Life originated on some planet & traveled to Earth through space • Life originated by unknown means on Earth • Life evolved from nonliving substances through interaction with the enviorment

  8. 17.3 The Beginnings of Life • Other explanations (supernatural forces or a deity) aren’t within scope of science because we can’t use science to confirm or reject it

  9. Oparin-Haldane • Environmental energies (radiation, lightning, & heat) provided the energy needed to cause atmospheric gases to form organic compounds • The organic compounds formed a “primordial soup”

  10. Oparin-Haldane • Both believed 1st life forms fed on the “soup” = heterotrophs • Heterotroph Hypothesis: • Need a supply of organic molecules produced by nonbiological sources • Processes had to create polymers from the small organic molecules • Processes had to organize the polymers so they could self-replicate

  11. Miller & Urey • Is it possible to make organic compounds from inorganic compounds? • Built an apparatus in a lab that simulated early atmosphere - added all the gasses that were present (methane, ammonia, water vapor, hydrogen), a spark = lightning, a condenser = rain to cool gasses

  12. Miller & Urey • Able to accumulate a liquid containing organic molecules = amino acids & with some changes bases and ribose sugar

  13. Miller & Urey

  14. A.G. Cairns-Smith • Hypothesized that clay particles helped catalyze the first polymers • Clay = repeating crystal structures that can attract certain molecules like amino acids • The crystals could have then catalyzed the bonding between these to form polymers • We are still left with many questions but we have a possibility

  15. “Chicken & the Egg” • Self-replication = chicken & the egg problem • DNA = universal information molecule for life on Earth • Replication of DNA requires proteins but proteins are coded for by DNA • Seems impossible to make proteins without DNA & DNA without proteins

  16. Possible Solution to Chicken & the Egg • RNA-world Hypothesis Components of RNA can be produced from inorganic compounds & can join spontaneously and some can catalyze their own partial replication RNA served as the 1st information molecule & the catalyst

  17. 17.5 Biological Evolution • NASA’s definition of life: • A self-sustained chemical system that is capable of undergoing Darwinian or biological evolution • Origin of life = beginning of biological evolution

  18. 17.5 Biological Evolution • 3 processes needed for biologial evolution: • Self-reproduction • Inheritable mutations • Natural selection

  19. 17.5 Biological Evolution • Cell theory = all life is made of cells, so how did cells arise? • To get a cell, we need a cell membrane (to separate it from the outside) • Still not clearly understood where cells & their membranes came from

  20. 17.5 Biological Evolution • Carl Woese proposed a model for formation of 1st cells • Cells formed with the help of the “greenhouse effect” produced by carbon dioxide; meteors hit earth creating large amount of dust which got covered with water droplets

  21. 17.5 Biological Evolution • The droplets were warmed by the atmosphere & acted like the first cells in which reactions could occur

  22. 17.7 Eukaryotes • First life = prokaryotes, ~3.5 billion years old • Endosymbiont Theory (Margulis) • Symbiosis – an ecological relationship between organisms of two species that live together in direct contact

  23. 17.7 Eukaryotes • Endosymbiont Theory (Margulis) • Margulis proposed that eukaryotes began from a symbiosis between a large anaerobic prokaryote and a smaller aerobic or photosynthetic prokaryote. • The large cell absorbed the smaller one & the smaller cell survived within the host (eventually becoming a mitochondrion or chloroplast)

  24. 17.7 Eukaryotes • Endosymbiont Theory (Margulis) • The endosymbionts (internal partners) lost the ability to live independently

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