Chapter 26: Origin of life

Figure 26.2 Clock analogy for some key events in evolutionary history

Unnumbered Figure (page 512) Evolutionary clock: Origin of life

Unnumbered Figure (page 512) Evolutionary clock: Prokaryotes

HISTORY OF LIFE Earth is 4.5 billion years old Oldest rock Contains isotopes of carbon Oldest fossils 3.5 billion years old Stromatolites Banded domes of sedimentary rock Resemble layered mats of cyanobacteria today Probably photosynthetic but not the first life form

Figure 26.0x Volcanic activity and lightning associated with the birth of the island of Surtsey near Iceland; terrestrial life began colonizing Surtsey soon after its birth

Figure 26.1 Some major episodes in the history of life

Figure 26.3 Early (left) and modern (right) prokaryotes

Figure 26.4 Bacterial mats and stromatolites

Figure 26.3x1 Spheroidal Gunflint Microfossils

Figure 26.3x2 Filamentous cyanobacteria from the Bitter Springs Chert

ONE HYPOTHESIS SCENARIO Abiotic synthesis of organic monomers CONDITIONS ON EARTH Atmosphere had little O2 Intense Lightning Volcanic activity Meteorite bombardment UV radiation SCENARIO Abiotic synthesis of organic monomers Abiotic synthesis of polymers Formation of protobionts Origin of hereditary material

OPARIN & HALDANE 1920s Worked independently Postulated Conditions on primitive Earth favored abiotic synthesis of organic material Atmosphere Contained less O2 Less oxidizing than today’s More reducing than today’s

MILLER & UREY 1953 Tested Oparin & Haldane hypothesis Created early Earth conditions in lab Atmosphere: H2O, H2, CH4, NH3 Added spark Created organic material Other labs have created All 20 AA Some sugars & lipids Purine & pyrimidine bases ATP

Figure 26.10 The Miller-Urey experiment

ABIOTIC SYNTHESIS OF POLYMERS Example: connecting amino acids (AA) together to form proteins Occurred without enzymes Evidence Synthesis of protenoids Drip of sol’n of AA on hot sand or clay AA bonded together to form protein Zn and Fe ions act as catalysts

FORMATION OF PROTOBIONTS Aggregates of abiotically produced molecules with an internal environment different from external First primitive “cells” Evidence Coacervates Proteinoids Microspheres Liposomes

ORIGIN OF HEREDITY Genetic information made it possible to pass along information for making new molecules Today: DNA  RNAProtein Originally: RNA  protein Support RNA acts as enzyme (ribozymes) Synthesized short segments of RNA in lab; replicate short segments of RNA without enzymes

Figure 26.11 Abiotic replication of RNA

Figure 26.13 Hypothesis for the beginnings of molecular cooperation

MAJOR LINEAGES OF LIFE 5 Kingdoms Monera Protista Plantae Fungi Animalia Domains Bacteria Archaea Eukarya 5 proposed protist kingdoms!!! Kingdom Plantae Kingdom Fungi Kingdom Animalia

Figure 26.15 Whittaker’s five-kingdom system

Figure 26.16 Our changing view of biological diversity