Origins of Life The Tree of Life Cell is the basic unit of life Today all cells come from pre-existing cells Earth formed ~4.5 billion years ago (BYA) Chapter 26 As it cooled, chemically-rich oceans were formed from water condensation Life arose spontaneously Ocean s edge, hydrothermal deep-sea vents, or elsewhere 2 Fundamental Properties of Life Cellular organization Sensitivity Growth Development Reproduction Regulation Homeostasis Heredity Panspermia Earth may have been infected with life from some other planet Meteor or cosmic dust may have carried complex organic molecules to earth Kicked off evolution of life 3 4
Conditions on Early Earth First organisms emerged ~3.5 BYA Seems likely that Earth s first organisms emerged and lived at very high temperatures Early atmosphere composition not agreed on May have been a reducing atmosphere Would have made it easier to form carbon-rich molecules In 1953, Miller and Urey did an experiment that reproduced early atmosphere Assembled reducing atmosphere rich in hydrogen with no oxygen gas Atmosphere placed over liquid water Temperature below 100ºC Simulate lightning with sparks 5 6 Methane gas (CH 4 ) converted into other simple carbon compounds Compounds combined to form simple molecules and then more complex molecules Later experiments produced more than 30 carbon compounds including amino acids Adenine also produced 7 8
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Eons Eras Periods RNA may have been first genetic material Ribozyme activity Amino acids polymerized into proteins Metabolic pathways emerged Primitive organisms may have been autotrophic built what they needed Lipid bubbles could increase the probability of metabolic reactions Leads to cell membranes Other innovations contributed to diversity of life Precambrian Hadean Archaean Proterozoic Late Middle Early Late Middle Early 500 MYA 1000 MYA 1500 MYA 2000 MYA 2500 MYA 3000 MYA 3500 MYA 4000 MYA 4500 MYA Appearance of animals and plants First multicellular organisms Oldest definite fossils of eukaryotes Appearance of oxygen in atmosphere Cyanobacteria Oldest fossils of prokaryotes Molten-hot surface of Earth becomes somewhat cooler Oldest rocks Formation of Earth Supercontinent of Gondwana forms. Oceans cover much of North America. Climate not well known. Most of Earth is covered in ocean and ice. 9 10 Eons Eras Cenozoic Periods Quaternary Tertiary Present 50 MYA Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Appearance of humans First primate Bird radiation Mammal radiation North and South America joined by land bridge. Uplift of the Sierra Nevada. Worldwide glaciation. Grouping Organisms 6 kingdom system Pollinating insects Cretaceous 100 MYA Diversification of flowering plants Mesozoic Jurassic 150 MYA First flowering plants, birds, marsupial mammals Gondwana begins to break apart; interior less arid. Gondwana Phanerozoic Triassic Permian 200 MYA 250 MYA First dinosaurs First gymnosperms Pangea intact. Interior of Pangea arid. Climate very warm. Prokaryotes Eukaryotes 300 MYA First reptiles Paleozoic Carboniferous Devonian 350 MYA 400 MYA First amphibians Bony fish, tetrapods, seed plants, Supercontinent of Laurentia to the north and Gondwana to the south. Climate mild. Laurentia Gondwana and insects appear Silurian Early vascular plants diversify 450 MYA Ordovician Invertebrates dominate First land plants Cambrian 500 MYA Cambrian explosion; increase in diversity 11 12
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Domain Bacteria (Bacteria) Domain Archaea (Archaebacteria) Domain Eukarya (Eukaryotes) Common Ancestor a. 3 domain system Domain Archaea Domain Bacteria Domain Eukarya 13 Tree based on rrna analysis Archaea and Eukarya are more closely related to each other than to bacteria 14 Bacteria 15 Most abundant organisms on Earth Key roles in biosphere Extract nitrogen from the air, and recycle carbon and sulfur Perform much of the world s photosynthesis Responsible for many forms of disease Highly diverse Most taxonomists recognize 12 15 different groups 16
Archaea Shared characteristics Cell walls lack peptidoglycan (found in bacteria) Membrane lipids are different from all other organisms Distinct rrna sequences Divided into three general categories Methanogens Extremophiles Nonextreme archaea 17 Eukarya Prokaryotes ruled the earth for at least one billion years Eukaryotes appeared about 2.5 BYA Their structure and function allowed multicellular life to evolve Eukaryotes have a complex cell organization Extensive endomembrane system divides the cell into functional compartments 18 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Archaebacteria Animalia Fungi Protista Plantae Bacteria Mitochondria and chloroplasts most likely arose by endosymbiosis Mitochondria were derived from purple nonsulfur bacteria Chloroplasts from cyanobacteria Thermophiles Halophiles Methanogens Nonphotosynthetic protists Ancestral eukaryotic cell Brown algae Red algae Green algae Photosynthetic protists Mitochondria Chloroplasts Purple bacteria Photosynthetic bacteria Other bacteria 19 20
Viruses Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Are literally parasitic chemicals DNA or RNA wrapped in protein Cannot reproduce on their own Not considered alive cannot be placed in a kingdom Viewed as detached fragments of a genome Vaccinia virus (cowpox) Herpes simplex virus Rhinovirus (common cold) Adenovirus (respiratory virus) Influenza virus HIV-1 (AIDS) Poliovirus (polio) T4 bacteriophage Tobacco mosaic virus (TMV) 100 nm 21 22 Ebola virus