1. Chapter 14: History of Life Modern Biology © 2009. Holt, Rinehart, & Winston, pp 278-290.

2. Biogenesis vs. Spontaneous Generation Biogenesis – Current view – All life comes from preexisting life Precept of the Cell Theory Spontaneous Generation – Popular before 1600s – Life could arise from nonliving things Maggots from rotting meat Fish from dried ponds

3. Spontaneous Generation Frogs from Mud utenti.quipo.it study.com

4. Francesco Redi (1626-1697) Redi noted that maggots arose where adult flies had previously landed Maggots turned into sturdy oval cases Flies emerged from those oval cases Did 1 st experiment in 1668 showing that maggots only arose from uncovered meat. – Concluded flies gave rise to maggots, not the meat

5. Redi’s Xp: bio.miami.edu

6. Lazzaro Spallanzani (1729-1799) Tested if microorganisms arose spontaneously Had 2 separate groups of broth-filled flasks Boiled broth in all flasks Left 1 group open to the air but sealed others Only broth in the open flasks became cloudy Opposition claimed air’s “vital force” was absent from closed container & this prevented microorganisms’ growth

7. Spallanzani’s xp angelfire.com

8. Louis Pasteur (1822-1895) Addressed Spallanzani’s experimental design – Air’s “vital force” must have access to broth Used broth in curved-necked flasks – Curve allowed air exchange with the room – Curve prevented solid particles’ entry to flask Boiled broth to kill microorganisms in flasks Left flasks undisturbed for a year  clear Broke off curved neck allowing access to air After 1 day  broth was cloudy

9. amoebamike.wordpress.com

10. Life in a New Solar System Our Solar System’s History – Initially part of swirling mass of stellar dust & gas – Gravity pulled most together  our sun – Occurred around 5 x 10 9 years ago Our Planet’s History – Dust & gas continued revolving around sun’s mass – Debris continually collided with itself  planets Earth formed over ~ 4 x 10 8 yr span of collisions

12. Estimating Age Geological history = stratification of surface Radiometric dating Different isotopes have different half-lives – Radioactive isotopes have constant half-lives C-14 = 5.7 X 10 3 yrsU-238 = 4.5 x 10 9 yr U-235 = 7 x 10 8 yrs Th-232 = 1.4 x 10 10 yrs Calculate age of sample by comparing quantities of stable element with its isotope

13. Earth’s History Oldest rocks & crystals = ~ 4 x 10 9 yrs – Collisions with space debris ceased Proposed early atmosphere – NH 3 or N 2, H 2, H 2 O, & CH 4 or CO 2 Synthesis of Organic Compounds – Miller-Urey Apparatus tested Oparin’s hypothesis – Treated compounds with heat & electricity – Produced amino acids; later ATP & nucleotides too

14. Simple organic compounds

15. Molecules to 1 st Cell-like Structures Fox, et al, mixed simple organic compounds Spontaneous formation of cell-like structures – Microspheres Protein molecules Membrane organization – Coacervates Collections of droplets Composed of lipids, amino acids, & sugars No response to natural selection – No hereditary material

16. Miller-Urey Xp:

17. First Life Forms RNA may have been critical macromolecule – Ribozyme; self-replication; basic biochemistry 1 st cells? anaerobic, heterotrophic prokaryotes – Ate up spontaneously formed organic molecules 1 st autotrophs likely did chemosynthesis – CO 2 = C source; energy from oxidizing inorganics – Archaea/ archaebacteria: hostile environments Photosynthetic prokaryotes @ 3.5 x 10 9 yrs – Fossils look like our current cyanobacteria – Produced O 2  10 9 yrs  our atmosphere today

18. Photosynthetic Prokaryote

19. First Eukaryotes Differences – Larger cells; DNA in chromosomes inside nucleus – Membrane-bound organelles Theory of Endosymbiosis – Aerobic prokaryotes engulfed by eukaryote – Modern Chloroplasts & Mitochondria Evidence – Independent replication – Contain some unique DNA which is circular

20. biology-forums.com