The Earth and The Origin of Life (Chapter 26)

1. The Earth and The Origin of Life(Chapter 26)

2. Introductory Questions #1 • What were the molecules thought to exist in the early atmosphere? • What does it mean when we say that this early atmosphere was a “reducing” atmosphere? • What is the significance of Miller’s experimetn in the 1950’s? • What are protobionts and microspheres? • Where can Stomatolites be found? What are they composed of? • What is the predominant thought of how Polymerization might of occurred? • Was the first organisms thought to be heterotrophs or Autotrophs? Explain.

3. Chemical Evolution & Formation of Macromolecules • Solar System: formed approx. 12 billion years ago • Earth is Approx. 4.6 Billion Years ago • Early Atmosphere was thought to be composed of: • CO2 Water Vapor • CO H2 • N2 NH3 (ammonia) • H2S CH3 (methane) • Reducing Atmosphere (molecule forming) • First Life form originated approx. 3.8 billion years ago

4. Early History of life

5. Early History of life • Solar system~ 12 billion years ago (bya) • Earth~ 4.5 bya • Life~ 3.5 to 4.0 bya • Prokaryotes~ 3.5 to 2.0 bya stromatolites • Oxygen accumulation~ 2.7 bya photosynthetic cyanobacteria • Eukaryotic life~ 2.1 bya • Multicelluar eukaryotes~ 1.2 bya • Animal diversity~ 543 mya • Land colonization~ 500 mya

6. Three Proposed Models • Pre-Biotic Soup Hypothesis (Oparin & Haldane) **proposed in 1920’s** • Iron-Sulfur Hypothesis (Hydrothermal vents) • Seeded Meteorite impact

7. The Origin of Life • Spontaneous generation vs. biogenesis (Pasteur) • The 4-stage Origin of life Hypothesis: • 1- Abiotic synthesis of organic monomers • 2- Polymer formation • 3- Origin of Self-replicating molecules • 4- Molecule packaging (“protobionts”)

8. Organic monomers/polymer synthesis • Oparin (Rus.)/Haldane (G.B.) hypothesis (primitive earth): volcanic vapors (reducing atmosphere) with lightning & UV radiation enhances complex molecule formation (no O2) • Miller/Urey experiment (1950’s): water, hydrogen, methane, ammonia all 20 amino acids, nitrogen bases, & ATP, DNA, and RNA were formed

9. How Polymerization could Occur? • Clay was thought to be a possible site for polymerization • Binds well to organic molecules • Contains Zinc, iron, nickel, etc serving as a catalyst • Has been shown to occur experimentally

10. Formation of the first Cells • Began as molecular aggregates (microspheres & protobionts) • Divide often (binary fission) • Grow larger in size • Maintain a level of homeostasis internally • Produce electrical potential across surfaces • Absorbs materials from the surface (selective permeability) • Catalytic activity

11. Molecular Replication • Usually involves DNA, RNA and proteins • All can form on clay surfaces • Self-replication common with DNA & RNA • Which formed first? DNA or RNA?

12. Molecular Replication • Most hypothesize that RNA was the first to form. Why? • RNA is a versatile molecule and: • Able to function both as an enzyme & substrate • Single stranded and easily forms H-bonds • Has catalytic properties • Can direct protein synthesis • Folds on itself and from various shapes

13. Abiotic Genetic Replication • First genetic material • Abiotic production of ribonucleotides • Ribozymes (RNA catalysts) • RNA “cooperation” • Formation of short polypeptides (replication enzyme?) • RNA~ DNA template?

14. Molecular cooperation led to the first cells controlled by RNA • Oldest fossilized cells widely accepted (2 bya) • Layers of Microorganisms & sediment called: Stromatolites First cells thought to be anaerobic using glycolysis as its metabolic pathway Heterotrophs → Photoautotrophs → Aerobes—Euk’s (O2 increases) (endosymbiotic theory)

15. The Major Lineages of Life

16. Figure 15.1

17. Key Fossil finds & Extinction Points • Ediacaran: oldest known fossils (600 mya) Australia • Burgess Shale: Cambrian explosion British Columbia • Permian Extinction: 90% of all marine life • Cretaceous Period: end of dinosaur fossils

19. Are Birds Really Dinosaurs with Feathers? • Did birds evolve from dinosaurs? • Evolutionary biologists investigate this question by looking at the fossil record

20. The fossil of the earliest known bird, Archeaopteryx, was discovered in 1861 • Fossils of dinosaurs with feathers may support the bird-dinosaur theory

21. The fossil record chronicles macroevolution • Macroevolution consists of the major changes in the history of life • The fossil record chronicles these changes, which have helped to devise the geologic time scale

22. Figure 15.1

23. 15.2 The actual ages of rocks and fossils mark geologic time • The sequence of fossils in rock strata indicates the relative ages of different species • Radiometric dating can gauge the actual ages of fossils

24. 15.3 Continental drift has played a major role in macroevolution • Continental drift is the slow, incessant movement of Earth’s crustal plates on the hot mantle EurasianPlate NorthAmericanPlate AfricanPlate PacificPlate Splitdeveloping NazcaPlate SouthAmericanPlate Indo-AustralianPlate Antarctic Plate Edge of one plate being pushed over edge of neighboring plate (zones of violent geologic events) Figure 15.3A

25. CENOZOIC • This movement has influenced the distribution of organisms and greatly affected the history of life Eurasia North America Africa India SouthAmerica Australia • Continental mergers triggered extinctions • Separation of continents caused the isolation and diversification of organisms Antarctica Laurasia Millions of years ago MESOZOIC Gondwana Pangaea PALEOZOIC Figure 15.3B

26. Lungfishes evolved when Pangaea was intact • Continental drift explains the distribution of lungfishes Figure 15.3C

27. NORTHAMERICA ASIA EUROPE AFRICA SOUTHAMERICA AUSTRALIA = Living lungfishes = Fossilized lungfishes Figure 15.3D

28. 15.4 Connection: Tectonic trauma imperils local life • Plate tectonics, the movements of Earth’s crustal plates, are also associated with volcanoes and earthquakes • California’s San Andreas fault is a boundarybetween two crustal plates San Andreas fault San Francisco Santa Cruz Los Angeles Figure 15.4A

29. Example: Galápagos • But volcanic activity can also destroy life • Example: Krakatau • By forming new islands, volcanoes can create opportunities for organisms Figure 15.4B, C

30. 15.5 Mass extinctions were followed by diversification of life-forms • At the end of the Cretaceous period, many life-forms disappeared, including the dinosaurs • These mass extinctions may have been a result of an asteroid impact or volcanic activity

31. ? Cretaceousextinctions 90 million years ago 80 70 65 60 Figure 15.5

32. Every mass extinction reduced the diversity of life • But each was followed by a rebound in diversity • Mammals filled the void left by the dinosaurs