Origins and History of Life

Origin of Life Hypothesis of today: inorganic molecules in Earth’s prebiotic oceans combined to produce organic molecules  primitive cells.  Spontaneous orgin  Chemical evolution Extraterrestrial origin Divine Creation

Time line 10 billion years – sun, planets 4.6 bya – solar system in place, earth’s crust  Atmosphere formed by gravitational field Water vapor, nitrogen, carbon dioxide, hydrogen, methane, ammonia, hydrogen sulfide and carbon monoxide 3.5 bya – prokaryotic cells

A.I. Oparin, 1920’s Russian biochemist Abiotic synthesis – formation of simple monomers (AA, sugars) from inorganic molecules  Use of energy sources (volcanoes, lightning…) Primordial soup model

Stanley Miller, 1953 Harold Urey Tested primordial soup hypothesis Produced organic molecules

Polymers evolve Sidney Fox – Protein first hypothesis  AA polymerize when exposed to heat  proteinoids  microspheres (composed of proteins but have properties of a cell) Graham Cairns Smith – Clay  Helpful in causing polymerization of monomers to produce proteins and nucleic acids RNA-first hypothesis –  RNA can be both substrate and an enzyme, genetic material of viruses

Protocell Before true cell Lipid-protein membrane (liposome), carries on energy metabolism Liposomes – formed double layered bubbles when in water, may have provided life’s first boundary. Chemical evolution  biological evolution  Figure 19.4, p321

History of Life Fossils – remains and traces of past life  Trails, footprints, bone, shell, teeth Paleontology – discovering and studying of the fossil record Sedimentation – weathering and erosion of rocks  sediment  stratum (layer in a stratigraphic sequence.

Relative/absolute dating of fossils Relative dating – strata of the same age contain fossils of the same organisms Absolute dating – use radioactive dating techniques, gives actual date of fossil  Uses half-life of radioactive isotope to stable element  Use C14 isotope for things that contain organic matter

Geological Timescale era, period, epoch Table 19.1 Precambrian period – 87% of time scale  4.6 bya – 600 mya  Photosynthesizing organisms, O2 in atmosphere  3.5 bya = prokaryotes  2.7 ozone (oxygen enters)  2.2 eukaryotic  1.4 protists

Paleozoic era 599 mya – 251 mya Plants evolve on land – all types evolve Invertebrates, fish, amphibians, reptiles 3 mass extinctions Carboniferous period – great coal-forming forest

Mesozoic Triassic, Jurassic and Cretaceous periods 251 mya – 65.5 mya Flowering plants evolve First small mammals, Dinosaurs, birds, placental mammals, modern insects 2 mass extinctions, Dinosaurs 65 mya

Cenozoic Tertiary period  65.5 mya – 2 mya  Flowering plants flourish  Primates to early humans, hominids  Mammal diversity, human evolution begins Quartenary period  Present  Modern humans, Homo sapien  Human influence on plants

Factors that influence evolution Continental drift – continents are not fixed, their positions and positions of oceans have changed Permian period – 1 land mass  pangaea  Divided into 2 large land masses Laurasia Gondwana  Then split into continents we know today

Plate tectonics Branch of geology Tectonics – movement of earth’s crust Earth’s crust is fragmented into slab-like plates that float on a lower hot mantle layer

Mass Extinctions Disappearance of a large number of species or higher taxonomic groups with an interval of just a few million years  At least 5  May be due to climate changes Continental drift Bolide – asteroid that explodes and produces meteorites that fall to earth  Found clay containing high levels of iridium, element found in asteroids