Origin of Life Biogenesis Earths History The First Life Forms
Biogenesis • Biogenesis • Spontaneous Generation • Francesco Redi -questioned that maggots spontaneously generated from rotting meat • Redi’s experiment proved maggots came from flies
Spallanzani • Microscopes allowed for viewing tiny organisms • Many believed organisms arose spontaneously from a “vital force” in the air • Spallanzani said microorganisms came from other microorganisms not “vital force” • SG backers said his experiment “destroyed” the vital force.
Pasteur • Experiment allowed in air (w/”vital force”) but prevented solid particles (microorganisms) from entering • Proved without doubt the concept of biogenesis
Earth’s age estimated using decay of uranium and thorium isotopes Age of oldest unmelted surface rock tells when collisions stopped in formation of earth. 4.2 billion years old. >4 billion years Radioactive dating Isotopes Mass no. = protons + neutrons Carbon-12 Carbon-14 (14C) Radioactive isotopes Radioactive decay Half-life Earth’s History
50% 75% 87.5% 93.75% 40K 10g 5g 2.5g 1.25 0 .625 Calculate the age of two specimen: • A human body buried in ice in which 87.5% of the carbon-14 decayed. • A meteorite in which 75% of the thorium-230 has decayed.
Alexander I. Oparin (1923) NH3, H2,H2O, CH4 and other carbon compounds At high temperatures could have formed amino acids Energy from lightning or uv rays then formed proteins or other organic polymers Miller and Urey Replicated Earth’s early conditions Produced variety of organic compounds including amino acids Other experiments produced aa, ATP, nucleotides of DNA Others hypothesize that conditions under hot springs favored production of organic compounds Another hypothesis: compounds arrived from space The First Organic Compounds
From Molecules to Cell Like Structures • Sidney Fox (1912-1998) • Microspheres • Coacervates • Both form spontaneously w/out help from enzymes • Polymerization on hot clay • Can grow or bud • No heredity
The First Life FormsThe Origin of Heredity • RNA can take different shapes b/c of H-bonds b/n nucleotides • RNA may behave like protein and catalyze reactions
RNA • Ribozyme- Thomas Cech (1946-) • Enzyme & replicate itself • Competition for nucleotides • Ribozymes have not produced other ribozymes • Could RNA be contained in microsphere or coacervate?
The First Prokaryotes • Heterotrophs-competition • Archaebacteria • Chemosynthesis • Photosynthesis- >3bya • Fossils in Australia, 3.5 byo • Stromatolites • Related to modern cyanobacteria • O2 in atmosphere react w/sunlight to form O3-Ozone
The First Eukaryotes • Infolding • Endosymbiosis • Mitochondria & Chloroplasts • Membranes • DNA — Each mitochondrion has its own circular DNA genome, like a bacteria's genome, but much smaller.