1. Chapter 14: History of Life (on Earth)
Modern Biology © Holt, Rinehart, & Winston, pp

4. Biogenesis vs. Spontaneous Generation
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

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

8. 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

10. 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

12. 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 109 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 108 yr span of collisions

14. 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 103 yrs U-238 = 4.5 x 109 yr
U-235 = 7 x 108 yrs Th-232 = 1.4 x 1010 yrs
Calculate age of sample by comparing quantities of stable element with its isotope

15. Earth’s History Oldest rocks & crystals = ~ 4 x 109 yrs
Collisions with space debris ceased
Proposed early atmosphere
NH3 or N2, H2, H2O, & CH4 or CO2
Synthesis of Organic Compounds
Miller-Urey Apparatus tested Oparin’s hypothesis
Treated compounds with heat & electricity
Produced amino acids; later ATP & nucleotides too

17. Molecules to 1st 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

20. Cyanobacteria structure

21. First Life Forms RNA may have been critical macromolecule
Ribozyme; self-replication; basic biochemistry
1st cells? anaerobic, heterotrophic prokaryotes
Ate up spontaneously formed organic molecules
1st autotrophs likely did chemosynthesis
CO2 = C source; energy from oxidizing inorganics
Archaea/ archaebacteria: hostile environments
Photosynthetic 3.5 x 109 yrs
Fossils look like our current cyanobacteria
Produced O2  109 yrs  our atmosphere today

22. Earliest Evidence for life on Earth

23. Cyanobacteria

24. First Eukaryotes Differences Theory of Endosymbiosis Evidence
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