Chapter 14 History of Life Modern Biology 2009

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

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

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

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

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

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-235 = 7 x 108 yrs U-238 = 4. 5 x 109 yr Th-232 = 1. 4 x 1010 yrs • Calculate age of sample by comparing quantities of stable element with its isotope

Earth’s History • Oldest rocks & crystals = ~ 4 x 109 yrs – Collisions with space debris ceased • Proposed early atmosphere – NH 3 or N 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

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

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 109 yrs – Fossils look like our current cyanobacteria – Produced O 2 109 yrs our atmosphere today

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 of own DNA which is circular