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Origins of the Earth

Origins of the Earth. Our solar system formed 4.5 – 5 bya Earth – a coalescence of rocks ~ 4.5 bya After sufficient size, gravity strong enough to hold gases. Origins of Life. Early atmosphere Methane (CH 3 ) Carbon dioxide (CO 2 ) Ammonia (NH 3 ) Hydrogen (H 2 ) Nitrogen (N 2 )

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Origins of the Earth

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  1. Origins of the Earth • Our solar system formed 4.5 – 5 bya • Earth – a coalescence of rocks ~ 4.5 bya • After sufficient size, gravity strong enough to hold gases

  2. Origins of Life • Early atmosphere • Methane (CH3) • Carbon dioxide (CO2) • Ammonia (NH3) • Hydrogen (H2) • Nitrogen (N2) • Water vapor (H2O) • C, N, H, and O are basic elements of life

  3. Origins of Life • Early Earth inhospitable • Once begin cooling, condensation • Formation of oceans • Set stage for first life – about 3.5 bya

  4. How Can We Look Back Billions of Years • Principle of Continuity – Any stage of life’s evolution should derive from preexisting states. • Signature Principle – Prebiotic processes should be evident in biochemistry of modern life • No-free-lunch Principle – all life requires energy to grow

  5. Hypotheses and Testing • These three principles + essentials of life allow for generation of testable hypotheses on formation of life • Essentials of Life • Described in introductory lecture

  6. Origins of Life • No free oxygen in early atmosphere • But doesn’t all life require oxygen? • Precursors for life – simple molecules (remember hierarchy of life) • Stanley Miller’s Experiments (1950s)

  7. Reaction formed simple molecules Simple molecules formed amino acids, purines, and pyrimidines

  8. Building Blocks of Life • Molecules (amino acids, etc.) are not life • Building blocks would continue to accumulate • Next step would be formation of macromolecules (proteins, polysaccharides, nucleic acids) • Formed by polymerization (repeated condensation of monomers – Chapter 3) • Key is a lot of building blocks needed

  9. Building Blocks of Life • Molecules are not life – prebiotic • For life, three other conditions must be met: • Replicators – self-reproducing molecules • Error via mutation • Energy and partial isolation from environment

  10. Isolation from Environment • Why? • Eliminate interference with chemical reactions • Protobionts • Aggregates of prebiotic molecules that create an isolated internal environment • Produced experimentally in 1920s

  11. Replicator Molecules • RNA was probably first • Experiments in 1970s and 1980s demonstrated that RNA could use simple molecules to build nucleotides and more complex molecules • A replication error could lead to DNA later after living organisms present

  12. First Life • A collection of protobionts • Contain all the essentials of life • Probably a heterotrophic bacteria • Feeding on organic molecules • Anaerobic

  13. We will continue topics on the orgins of prokaryotic and eukaryotic life later as we move through those groups

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