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Early Earth and The Origin of Life Chapter 20 The Origin and Evolution of Life Chapter 20 The Big Bang • 12-15 billion years ago all matter was compressed into a space the size of our sun • Sudden instantaneous distribution of matter and energy throughout the known universe Earth Forms • 4,600 mya: Origin of Earth • 4,600 - 3,800 mya – Formation of Earth’s crust, atmosphere – Chemical and molecular evolution – First cells (anaerobic bacteria) Earth Forms • About 4.6 and 4.5 billion years ago • Minerals and ice orbiting the sun started clumping together • Heavy metals moved to Earth’s interior, lighter ones floated to surface • Produced outer crust and inner mantle Earth Is “Just Right” for Life • Smaller in diameter, gravity would not be great enough to hold onto atmosphere • Closer to sun, water would have evaporated • Farther from sun, water would have been locked up as ice First Atmosphere • Hydrogen gas • Nitrogen • Carbon monoxide • Carbon dioxide • No gaseous oxygen Origin of Organic Compounds • Amino acids, other organic compounds can form spontaneously under conditions like those on early Earth • Clay may have served as template for complex compounds • Compounds may have formed near hydrothermal vents • Oparin hypothesized that energy from lightning could have caused organic molecules to form from inorganic compounds in Earth’s primitive atmosphere. Miller-Urey Experiment • In 1953, Miller and Urey did an experiment that simulated lab conditions that were similar to those of the early Earth • After one week, they found a variety of organic compounds (including amino acids) that had been produced from inorganic material Miller-Urey Experiment Chemical Evolution • Spontaneous formation of porphyrin rings from formaldehyde • Components of chlorophylls and cytochromes chlorophyll a formaldehyde porphyrin ring system Figure 20.4 Page 720 RNA World • DNA is genetic material now • DNA-to-RNA-to-protein system is complicated • RNA may have been first genetic material • RNA can assemble spontaneously and can carry out enzyme-like catalytic functions. (These enzyme-like, self-replicating pieces of RNA are known as ribozymes.) • How switch from RNA to DNA might have occurred is not known. Ribozymes might have somehow served as a template for DNA production. Proto-Cells • Microscopic spheres of proteins or lipids can self assemble • Tiny sacs like cell membranes can form under laboratory conditions that simulate conditions in evaporating tidepools Protobionts • Collections of abiotically produced molecules surrounded by a membrane • Exhibit simple reproduction and metabolism. • Small membrane bound droplets called liposomes can form when lipids are added to water. Possible Sequence membrane-bound proto-cells living cells self-replicating system enclosed in a selectively permeable, protective lipid sphere DNA RNA formation of protein-RNA systems, evolution of DNA enzymes and other proteins formation of lipid spheres spontaneous formation of lipids, carbohydrates, amino acids, proteins, nucleotides under abiotic conditions Figure 20.5 Page 331 Proterozoic Eon • Origin of photosynthetic Eubacteria – Noncyclic pathway first – Cyclic pathway next • Oxygen accumulates in atmosphere • Origin of aerobic respiration The First Cells • Originated in Archeon Eon • Were prokaryotic heterotrophs • Secured energy through anaerobic pathways – No oxygen present – Relied on glycolysis and fermentation History of Life ARCHAEBACTERIAL LINEAGE ANCESTORS OF EUKARYOTES ORIGIN OF PROKARYOTES Noncyclic pathway Cyclic pathway of of photosynthesis photosynthesis Aerobic respiration Figure 20.6 Page 332 3.8 bya 3.2 bya 2.5 bya History of Life ARCHAEBACTERIA Extreme halophiles Methanogens Extreme thermophiles ORIGINS OF EUKARYOTES ORIGINS OF MITOCHONDRIA ORIGINS OF ANIMALS EUKARYOTES Animals Heterotrophic protistans ORIGINS OF FUNGI Fungi Photosynthetic protistans ORIGINS OF PLANTS Plants ORIGINS OF CHLOROPLASTS EUBACTERIA Photosynthetic oxygen producers Other photosynthetic bacteria Chemotrophs, heterotrophs 1.2 bya 900 mya 435 mya present Figure 20.6 Page 332 Advantages of Organelles • Nuclear envelope may have helped to protect genes from competition with foreign DNA • ER channels may have protected vital proteins DNA Figure 20.10 Page 335 infolding of plasma membrane Theory of Endosymbiosis • Lynn Margulis • Mitochondria and chloroplasts are the descendents of free-living prokaryotic organisms • Prokaryotes were engulfed by early eukaryotes and became permanent internal symbionts Timeline of Life on Earth Kingdoms of Life • Arranging the diversity of life into kingdoms is a work in progress • There are multiple ways to categorize the forms of life • Some diagrams to be familiar with… Kingdoms of Life Most do not use this 5 kingdom system today! Kingdom Monera has been divided into two kingdoms. Kingdoms of Life Classification Levels • • • • • • • • Domain Kingdom Phylum/Division (for plants & fungi) Class Order Family Genus Species Classification Scheme • • • • • • • • Based on work of Carolus Linnaeus Father of taxonomy Father of binomial nomenclature Genus species Genus is a noun that describes the organism. Species name is an adjective describing it. Genus (capitalized & underlined) species (never capitalized & underlined) Classification of Living Things Domain Kingdom Cell Type Bacteria Archaea Eubacteria Archaebacteria Prokaryote Prokaryote (no membrane bound nucleus; few membranous organelles) Cells walls Cell Structures with peptidoglycan Protista Eukaryote (Membranebound nucleus with many organelles) Fungi Eukaryote Eukarya Plantae Eukaryote Cell walls without peptidoglycan Cells calls of Cell walls with cellulose in chitin some; some have chloroplasts Cell walls of cellulose; chloroplasts Animalia Eukaryote No cell walls; No chloroplasts # of cells Unicellular Unicellular Most Unicellular; some simple multicellular Most multicellular; Multicellular some unicellular (yeasts) Multicellular Mode of Nutrition Autotroph or Heterotroph Autotroph or Heterotroph Autotroph or Heterotroph Heterotroph Autotroph Heterotroph Examples Streptococcus; Methanogens, Escherichia Halophiles coli Thermophiles Amoeba; Paramecium; Euglena Algae; Kelp Mushrooms; molds; mildew; yeast Mosses; ferns, gymnosperms(co nifers); Angiosperms (flowering plants) Sponges, worms, insects, fishes, mammals, etc.
