BI305-Life on Earth and Endosymbiotic Theory PDF

BI305-Life on Earth and Endosymbiotic Theory DR. ALLISON E. MCDONALD Microfossils? Apex Chert, North Pole, Australia Testing the Biogenicity of Microfossils  mm-scale morphology  Carbon isotopic composition of the fossils or associated materials  Chemical composition of the obj...

BI305-Life on Earth and Endosymbiotic Theory DR. ALLISON E. MCDONALD Microfossils? Apex Chert, North Pole, Australia Testing the Biogenicity of Microfossils  mm-scale morphology  Carbon isotopic composition of the fossils or associated materials  Chemical composition of the objects  All 3 must be satisfied to suggest that microfossils are of biological origin  Very difficult to do Carbon Isotope Signatures  2 stable isotopes of carbon: Carbon 12 and Carbon 13  Abiotic ratio in mineral compounds is 89  Biotic ratio due to a preference of enzymes for Carbon 12 is 92 Very Early Earth (4500-3800 Mya)  No atmosphere  Volcanic activity  Bombardment by objects from space  Outgassing of water vapour, carbon monoxide, carbon dioxide, nitrogen, hydrogen from the various layers of the planet  Very hot Early Earth (~3800 Mya)  Planet starts to cool  Water condenses to form oceans  Volcanic activity  Atmosphere starts to form-comprised of nitrogen, carbon dioxide, carbon monoxide, water vapour, hydrogen, and methane  High levels of ultraviolet radiation  Torrential rain and lightning Hypotheses for the Origin of Life on Earth  Exogenesis/Panspermia  Abiogenesis  RNA World  Metabolism First Models Exogenesis  Life originated elsewhere in the universe and the Earth was “seeded” with this life by meteoroids, asteroids, and planetoids Exogenesis  Requirements Life must be able to survive travel through space Life must be able to survive impacts into Earth Life must have existed elsewhere in the universe prior to the “seeding” of Earth Can Life Travel Through Space?  Horneck et al. 2001 put spores of the bacterium Bacillus subtilus into space for 2 weeks  Spores exposed to UV radiation did not survive  Spores protected from UV radiation by powder of clay, rock, or meteorites Can Life Survive Impact with Earth?  Tested by Burchell et al. in 2000  Fired projectiles coated with bacteria at 3.8/4.9 km/s at rock, glass, metal, and aerogel  Took samples from impact craters and materials ejected during the impact and cultured them  Bacteria were cultured from the ejecta from a rock surface  Authors stress that the results need to be replicated Is there life elsewhere in the universe?  Difficult to test  Currently scientists are looking in 2 ways: Sending robot probes to Mars SETI (Search for Extra Terrestrial Intelligence) Universal Pictures Hypotheses for the Origin of Life on Earth  Exogenesis  Abiogenesis  RNA World  Metabolism First Models Abiogenesis Abiogenesis  Life arose from inanimate inorganic and organic molecules through natural processes Abiogenesis  1871-Charles Darwin- life may have begun…"warm little pond, with all sorts of ammonia and phosphoric salts, lights, heat, electricity, etc. present, so that a protein compound was chemically formed ready to undergo still more complex changes". English Heritage Photo Library Abiogenesis  1924-Alexander Oparin and J. Haldane- "primeval soup" of organic molecules could be created in an oxygen-less atmosphere through the action of sunlight; “living matter evolving from self-replicating but nonliving molecules” Abiogenesis Origin of biological monomers Origin of biological polymers Transition from molecules to cells Abiogenesis  Requirements Formation of monomers must be possible under the conditions of early Earth Some explanation of transition from molecules to cells must be provided Urey-Miller Experiment Urey-Miller Experiment YassiYassine Mrabet Yaseen Mirabet Urey-Miller Experiment  Results 22 amino acids formed Several other organic compounds formed Problems o Relies upon a reducing atmosphere on early Earth and certain types of gases being present