Chap 26 Early Earth and the Origin of Life Hypotheses for Origin of Life on Earth • Divine origin • Extraterrestrial Origin • Abiotic Origin Earth is part of the _______ __ Galaxy The components for life are found in space. Eg. Amino acids .475 .7 1.7 2 3.5 3.8 4 • Alternatively, we can view these episodes with a clock analogy. Fig. 26.2 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Where did the first cell come from? Could life come from non-life? Spontaneous Generation of Life Abiogenesis • In 1862, Louis Pasteur conducted broth experiments that rejected the idea of spontaneous generation even for microbes. • A sterile broth would “spoil” only if microorganisms could invade from the environment. Cells must come from pre-existing cells BIOGENESIS Fig. 26.9 P 494 Ancient Reducing Atmosphere • Oparin and Haldane proposed that Earth’s ancient atmosphere was reducing rather than oxidizing –providing an environment where Abiogenesis could take place. • Why was there no free oxygen in Earth’s early atmosphere? • Why would the first life not evolve in an oxidizing atmosphere? Miller and Urey simulated Earth’s early atmosphere electricity simulated lightning Why should they have used uV light? An alternate atmosphere contained carbon monoxide, carbon dioxide, nitrogen gas and water vapor Experiments have produce all 20 amino acids, sugars, lipids, purines, pyrimidines What is the importance of amino acids? What is the importance of nucleic acids? Lightning and uV light provided energy for polymerization Chemical Evolution Abiogenesis • • • • • Proposed by Oparin and Haldane The abiotic synthesis of monomers Polymerization of monomers Aggregation of molecules into protobionts Origin of heredity Lightning and uV light provided energy for the formation of larger molecules and polymerization Adenine is an important percursosr P 495 Polymerization • When monomers dripped on to hot sand, clay or rock polymerization can occur • Clay concentrates amino acids and other monomers. Its charged surface can act as catalytic sites for polymerization. • Pyrite can also act as catalytic sites for polymerization Polymerization led to proteins and nucleic acids such as RNA • Liposomes behave dynamically, growing by engulfing smaller liposomes or “giving birth” to smaller liposomes. Fig. 26.12a Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • If enzymes are included among the ingredients, they are incorporated into the droplets. • The protobionts are then able to absorb substrates from their surroundings and release the products of the reactions catalyzed by the enzymes. Fig. 26.12b Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Protobiont Examples • Coacervate (Oparin) made of polypeptides nucleic acids and polysaccharides • Proteinoid Micorspheres (Fox) • Liposomes Protobionts • Aggregates of molecules that: • can start maintain a different internal environment (homeostasis) • can show rudimentary metabolism (catalytic reactions and modifications) • can show excitability (membrane potential) • can reproduce themselves • maintain genetic material RNA could not only replicate itself, but it could also act as a catalyst eg. Making proteins RNA with the best autocatalytic activity would predominate RNA - First Genetic Molecule 6. Natural section could refine protobionts containing hereditary information • Once primitive RNA genes and their polypeptide products were packaged within a membrane, the protobionts could have evolved as units. • Molecular cooperation could be refined because favorable components were concentrated together, rather than spread throughout the Fig. 26.13 2. Prokaryotes dominated evolutionary history from 3.5 to 2.0 billion years ago • Prokaryotes dominated evolutionary history from about 3.5 to 2.0 billion years ago. • supports the hypothesis that the earliest organisms were prokaryotes. • Relatively early, prokaryotes diverged into two main evolutionary branches, the bacteria and the archaea. – Representatives from both groups thrive in various environments today. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Oldest fossil is of a bacteria 3.5 Billion years old What are stramatolites? • Two rich sources for early prokaryote fossils are stromatolites (fossilized layered microbial mats) and sediments from ancient hydrothermal vent habitats. – This indicates that the metabolism of prokaryotes was already diverse over 3 billion years ago. Fig. 26.4 3. Oxygen began accumulating in the atmosphere about 2.7 billion years ago • Photosynthesis probably evolved very early in prokaryotic history. – The metabolism of early versions of photosynthesis did not split water and liberate oxygen. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Cyanobacteria, photosynthetic organisms that split water and produce O2 as a byproduct, evolved over 2.7 billion years ago. – This early oxygen initially reacted with dissolved iron to form the precipitate iron oxide. • This can be seen today in banded iron formations. – About 2.7 billion years ago oxygen began accumulating in the atmosphere and terrestrial rocks with iron began oxidizing. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • While oxygen accumulation was gradual between 2.7 and 2.2 billion years ago, it shot up to 10% of current values shortly afterward. • This “corrosive” O2 had an enormous impact on life, dooming many prokaryote groups. – Some species survived in habitats that remained anaerobic. • Other species evolved mechanisms to use O2 in cellular respiration, which uses oxygen to help harvest the energy stored in organic molecules. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings 4. Eukaryotic life began by 2.1 billion years ago • Eukaryotic cells are generally larger and more complex than prokaryotic cells. • In part, this is due to the apparent presence of the descendents of “endosymbiotic prokaryotes” that evolved into mitochondria and chloroplasts. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • While there is some evidence of earlier eukaryotic fossils, the first clear eukaryote appeared about 2.1 billion years ago. – Other evidence places the origin of eukaryotes to as early as 2.7 billion years ago. • This places the earliest eukaryotes at the same time as the oxygen revolution that changed the Earth’s environment so dramatically. – The evolution of chloroplasts may be part of the explanation for this temporal correlation. – Another eukaryotic organelle, the mitochondrion, turned the accumulating O2 to metabolic advantage through cellular respiration. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Endosymbiotic Theory Section 17-2 Chloroplast Aerobic bacteria Ancient Prokaryotes Nuclear envelope evolving Plants and plantlike protists Photosynthetic bacteria Mitochondrion Primitive Photosynthetic Eukaryote Ancient Anaerobic Prokaryote Primitive Aerobic Eukaryote Animals, fungi, and non-plantlike protists Mitochondria and Chloroplasts are thought to have been engulfed by Archaea Bacteria and formed the first eukaryotic cells - 3 bya 5. Multicellular eukaryotes evolved by 1.2 billion years ago • A great range of eukaryotic unicellular forms evolved into the diversity of present-day “protists.” • Multicellular organisms, differentiating from a single-celled precursor, appear 1.2 billion years ago as fossils, or perhaps as early as 1.5 billion years ago from molecular clock estimates. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 26.6 • Recent fossils finds from China have produced a diversity of algae and animals from 570 million years ago, including beautifully preserved embryos. Fig. 26.7 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings 6. Animal diversity exploded during the early Cambrian period 543 to 490 Million Years Ago • A second radiation of eukaryotic forms produced most of the major groups of animals during the early Cambrian period (after ice age). • Cnidarians (the plylum that includes jellies) and poriferans (sponges) were already present in the late Precambrian. 7. Plants, fungi, and animals colonized the land about 500 million years ago • The colonization of land was one of the pivotal milestones in the history of life. – There is fossil evidence that cyanobacteria and other photosynthetic prokaryotes coated damp terrestrial surfaces well over a billion years ago. – However, macroscopic life in the form of plants, fungi, and animals did not colonize land until about 500 million years ago, during the early Paleozoic era. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Old 5 Kingdom Classification system lumped all prokaryotic organisms into Monera Protista was found to be polyphyletic which led to it become broken up into smaller kingdoms Two distinct lines of Prokaryotes leads to the Three Domain system.