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Lecture 6

Lecture 6 - The Biological Record History of Life on Earth

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Environmental Science
Nick Eyles

Lecture 6 - The Biological Record: History of Life on Earth Monday, February 13, 2012 10:30 AM Poster project details on slides and Blackboard. A Very Short History of Life on Earth  Fossils  Step 1 The Earliest Bacteria: 3.8 Ga (?)  Step 2 The Cambrian Explosion: 542 Ma (multicellular animals with shells, backbones etc.)  Step 3 Diversification during the Paleozoic: c. 400-250 Ma  Step 4 Role of meteorites  NOVA DVD: Becoming Human How are fossils formed?  Shells buried and preserved unaltered (<100 million years)  Cavities filled with silica, calcium carbonate, iron - a process called mineralization  Minerals come through and replaced the creature o E.g. snail dies, falls to the bottom, soft parts get eaten away, sediments build up and bury it, sediments turn to rock, snail shell is affected by water that goes through the rocks (water is filled with minerals) and minerals replace shell  Uplift and erosion o Rock with fossils were uplifted and the layers were eroded so that is why you can see fossils at the level that we walk on Ammolite - an organic gemstone Ammonite fossils - iridescent aragonite with trace elements (Fe, Mn, Al, Ba) Trace Fossils  Preserved tracks, trails, burrows, borings  Study of trace fossils -ichnology  Process of disturbing sediment -bioturbation Fossils as clues to ancient environments Palaeoecology - study of ancient organisms and their environments Clues from  Fossil types,  Assemblages - group of fossils  Fossil morphology  Trace fossils Sea lilies - shallow water, crinoid (fancy name for sea lily), 6 feet tall, breaks up into rings Fossils and Stratigraphy  How do we use fossils in stratigraphy? o To establish relative age of rock units, correlate units  What information do we need to do this? o Relative age of rock units o Fossil species present in each unit o Establish time of first and last appearance of each species geologic range  William Smith  Principle of Faunal Succesion Cenozoic Era (Age of Recent Life) Mesozoic Era (Age of Medieval Life) Paleozoic Era (Age of Ancient Life) Precambrian What kinds of fossils are most useful for stratigraphic work?  Short-lived, widespread  Assemblages (groups) of species  Index fossils, e.g., Ammonites Trilobite Growth  Trilobites molted regularly  Thus very abundant in the fossil record  Intense meteorite bombardment from 4.5 to 4 Ga prevented life becoming establishment  No magnetic field to prevent oceans and atmosphere being stripped off the planet's surface by the solar wind The Oldest Fossil?  Sir James Dawson  1858 - Eozoon Canadense  'The dawn animal of Canada': now recognised as mineral not organic STEP 1: The earliest bacteria  Prokaryotes some are photosynthetic (called cyanobacteria: blue/green algae). o Microscopic, single celled, lacked a nucleus  The earliest prokaryotes (the Archaea) lived around superheated waters near submarine volcanic vents (hyperthermophilic) o Simple bag-like
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