2/18/2013 Where does life on Earth come from? • Spontaneous generation HISTORY OF LIFE principle that living things could arise from non living things ON EARTH • Biogenesis principle that states that all living things come from other living things EXPERIMENTS ON SPONTANEOUS GENERATION II. Needham - believed in spontaneous generation I. early 1700’s - attacked Redi’s work Francesco Redi - questioned spontaneous generation (said that flies actually came from eggs laid by flies on meat) Needham’s gravy experiment Redi’s meat experiment - control: open jar with raw meat in it - sealed jar with meat gravy and heated it supposedly - experimental: cheesecloth over jar with meat on it - let sit a few days killed any organisms in jar Results: - several days later he observed gravy under open jar- maggots microscope and found microbes cheesecloth jar- no maggots Conclusion - concluded that living organisms came from gravy no spontaneous generation IV. 1864 Luis Pasteur III. mid 1700’s Lazzaro Spallanzini (Italian) - finally disproved spontaneous generation - questioned spontaneous generation of maggots/flies - retested gravy experiment coming from rotting meat - felt Needham did not kill all organisms when heated Experiment: boiled nutrient broth in long curve necked flask gravy so retested experiment allowed air to enter, but no dust or other airborne particles Experiment: thoroughly boiled gravy in both jars, one open Results: after an entire year, and one sealed No microorganisms Results: Conclusion: open jar: microorganisms No spontaneous generation sealed jar: no micro. BIOGENESIS FINALLY Conclusion: BECAME CORNERSTONE OF BIOLOGY No spontaneous generation 1
2/18/2013 EARTH’S HISTORY • Gas and dust cloud condensed into a sphere Earth’s age: - about 4.6 billion years old - millions of years afterward volcanic activity and THEORIES meteorites showers shook the earth • Big Bang Theory - at about 3.8 billion years earth cooled and was - evidence shows 15 billion years ago universe was a concentrated super dense mass drenched with thundestorms for many thousands of - this mass exploded, hurled matter and energy into space years forming oceans - gravity pulled some matter together to form galaxies and stars - gravity also pulled matter into orbit around stars - water vapor (from meteorites, which contain ice ) in - sun attracted clumps of matter (planets), and planets attracted smaller atmosphere cooled to help form oceans clumps of matter (moons) - meteors: thought to be bits of material left over from formation of (thought this is where life first formed) our solar system. Determining the Age of the Earth By knowing the time of the half life and how many -radioactive dating: how age of have passed, number of years can be calculated earth determined by counting number of atoms left in sample. -radioisotope: unstable isotopes of certain elements that break down (decay) and lose neutrons. As they break down, they release charged particles (electrons) in the form of radioactivity -decay: changing of one element into another as elec. are given off - half life: time period in which half the initial number of atoms decay into atoms of the element they change into (non radioactive) FORMATION OF BASIC CHEMICALS Models of Formation of Life OF LIFE 1. Primordial Soup Model 1920’s: Oparin (Russian), Haldane (British) We have a good idea of how old the earth is • Atmosphere made of H2O vapor, NH3, CH4, and CO2 (no free O2- atmosphere couldn’t sustain life ) and how it formed, but what about life on earth? • Thunderstorm drenched earth • Oceans contained large amount of organic molecules (like soup with many vegetables and meats) Simple organic molecules energized by UV light and volcanic heat formed complex molecules • Molecules pushed together by energy of sun and lightening that became building blocks of first cells. • Molecules split, and formed new organic molecules (a.a., nucleic acids) 2
2/18/2013 1953: Miller, Urey Miller/Urey model later tested and proved incorrect. Tested primordial soup model by placing same molecules in chamber No ozone to protect earth so NH 4 and CH 4 with electric sparks. destroyed. After few days found No organic molecules made. organic molecules were formed. 2. Bubble Model 3. Organic compounds come from beyond earth from 1986: Luis Lerman meteorites rather than originating on the earth. (new hypothesis) Process to form life took place within bubbles on ocean’s surface. - CH 4 , NH 3 from undersea volcanoes were trapped in underwater bubbles and protected from UV - bubbles rose and burst releasing molecules into air - now exposed to UV in presence of O 2 and able to react NO ONE UNIFIED THEORY, BUT SCIENTISTS AGREE THAT LIFE FORMED FROM - organic molecules then NON LIVING MOLECUELS THRU A SERIES OF formed CHEMICAL REACTIONS. Organic Molecules become Cell Like Structures FIRST LIFE FORMS/ORIGIN OF HEREDITY Microspheres- spherical structures composed of many protein molecules organized as a membrane Why doesn’t DNA directly carry out protein synthesis? Coacervates- collections of droplets composed of different types of molecules (such as linked amino acids and sugars) - both can form spontaneously and contain lifelike properties It is hypothesized that some RNA molecules act * growth * reproduction- budding like proteins and catalyze reactions itself . * arise without direction from genes They are not alive because they do NOT have HEREDITY (due to ability to take different shapes) ***Microspheres may have led to cells*** 3
2/18/2013 DEVELOPMENT OF COMPLEX ORGANISMS Roles of RNA I. Prokaryotes • Ribozymes- type of RNA found in some unicellular eukarytoes A. archaebacteria: unicellular organisms which have no peptidoglycans - able to act as an enzyme and replicate itself in cell walls, unique lipids in cell membranes (Thomas Cech- early 1980’s) - thrived under harsh environmental conditions - most likely first organisms on earth • Self replicating RNA- new studies indicate that life may have started - probably anaerobes (very little oxygen present) this way - chemiautotrophs: CO 2 serves as carbon source to make - it would: organic molecules a. have heredity: be able to provide hereditary - evidence indicates eukaryotes evolved information that cell like structures lack from these b. be able to respond to natural selection and evolve - cyanobacteria : more modern photosynthetic bacteria that released oxygen into the atmosphere (3.5 billion years ago) II. Eukaryotes Endosymbiosis : mutually successful beneficial relationship between two organisms B. eubacteria: unicellular, contain peptidoglycans in cell wall and similar lipids in cell membrane as eukaryotes III. Land life mitochondria- evolved from Formation of ozone in upper atmosphere allowed life on land. non-photosynthetic bacteria invading bacteria This occurred about 2.5 billion years ago: - Cyanobacteria added oxygen to atmosphere from chloroplasts- evolved from photosynthetic bacteria photosynthesis. invading bacteria (closely related to - Oxygen destabilized by UV formed ozone. cyanobacteria) - both have own genes Sea life Plants & fungi Arthropods Vertebrates - able to replicate on their own (plasmids) 4
2/18/2013 100 million years ago land became covered with dense forests. First land life thought to be plants and fungi living together. (able to undergo photosynthesis) - Arthropods were first animals to invade land from sea (hard outer segmented exoskeleton, jointed limbs) Mutualism : relationship where both ex: lobsters, crabs, insects, spiders, scorpions organisms work together and benefit from each other - Vertebrates came next - came out of sea 370 M years ago Plants: evolved from photosynthetic a. fishes (very successful, ½ all modern vertebrates) protists (eukaryotes) b. amphibians (smooth skinned, four legs, need H 2 O) - couldn’t get minerals from rocks - ex: frogs, toads, salamanders Fungi: could absorb minerals from rock, c. reptiles (watertight skin, can stay in dry areas) - couldn’t make nutrients - ex: snakes, lizards, turtles, crocs d. mammals and birds - mycorrhizae : (fungus/roots) - birds evolved from feathered relationshiop between fungi dinosaurs during after Jurassic period and plants Mass extinction : episode where large numbers of species become extinct (due to weather or geologic changes on earth) In our earth’s history there were five mass extinctions: - 440 M years ago: end of Ordovician (fish and land invertebrates) - 360 M years ago: end of Silurian (small mammals) - 245 M years ago: end of Permian (96% of all species lost) - 65 M years ago: 2/3 all species gone including dinosaurs - 35 M years ago: not as devastating 5
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