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Lecture 6

Lecture 6

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Department
Environmental Science
Course
EESA06H3
Professor
Nick Eyles
Semester
Winter

Description
EESA06 Lecture 6 Page 1 EESA06 Lecture 6 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 Evolution of Earth: - Hadean Period – “hell on earth” - Rocks was molten, no water no atmosphere - Diversification – heavier elements sank to the middle - Magnetic field – to hold on to the gases – which build up atmosphere + oceans How are fossils formed? - Shells buried and preserved unaltered (<100 million years) - Mineralization - Cavities are filled with silica, calcium carbonate, iron (ex: tree stumps) - Most fossils are found in sedimentary rock o Exception: Pompeii people covered by pyroclastic flow and fossilized in ash Per-mineralization - Die in or near water - Soft parts consumed by bacteria - Sedimentation (fine grained =more detail, chemical makeup of rock = color) - More sediments pile on = pressure – rock - Mineral rich water = changes to the shell - Uplift – by continental crusts coming together (plate tectonics) - Erosion – wear away rocks Ammolite – an organic gemstone Ammonite fossils – iridescent aragonite with trace elements (Fe, Mn, Al, Ba) Trace Fossils - Preserved tracks, trails, burrows (protection/food), borings - Ichnology – study of trace fossils - Bioturbation – process of disturbing sediment Fossils as clues to ancient environments - Palaeocology – study of ancient organisms and their environments o (St.Cuthbert rings, Sea Lily - Crinoide) o Clues from: fossil types, assemblages (group of fossils tend to be found together), fossil morphology, trace fossils 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 EESA06 Lecture 6 Page 2 o Geologic range - Establish time of first and last appearance of each species William Smith – Principal of Faunal Succession – fossils appear in layers What kinds of Fossils are most useful for stratigraphic work? - Index Fossils (ex: Ammonites) - Are Short-lived and widespread - Assemblages (groups) of species Trilobite Growth - Trilobites molted regularly – shed skin - Thus very abundant in the fossil record The evolution of Life on Earth… - Intense bombardment from 4.5 to 4 Ga prevented life becoming established - No magnetic field to prevent oceans and atmosphere being stripped off the planet’s surface by the solar wind? Sir James Dawson – was wrong. - Thought to be the oldest fossil Eozoon Canadense (1868) – ‘the dawn of animal of Canada’ now recognized as mineral not organic – dubiofossil Step 1: The Earliest bacteria 3.3 Ga (?) - Prokaryotes – some are photosynthetic (called cyanobacteria: blue/green algae) o Microscopic, single-celled, lacking a nucleus - The earliest prokaryotes (the Archaea) lives around superheated waters near submarine volcanic vents (hyperthermophilic) o Simple bag-like cells o Only life forms between 3.8 and about 2 Ga Where on Earth did early life forms flourish? - Probably in oceans – salts, solvents, mixing of elements to create organic compounds EESA06 Lecture 6 Page 3 - Life forms may have first developed at hydrothermal vents (mid-ocean ridges) At Modern Hydrothermal vents (called smokers) on mid-ocean ridges: - Microbes – hydrothermophiles - Live at temps > 100C - No light - Energy from chemosynthesis – ex: sulfur Gunflint Formation (in Ontario) – prokaryotes - 1.9 billion – once thought to be the world’s oldest fossils Oldest Cyanobacteria are thought to be 3.5 billion years old from the Apex Chert in Western Australia - They may be dubio-fossils… entirely of mineral origin, not organic Stromatolites (Gk for ‘stoney carpet’) - most common Proterozoic fossils made up of colonies of prokaryotic bacteria trapping fine sediment on sticky bacterial mats - Modern relatives still survive in hyper-saline lagoons in western Australia The “Rusting” of the Earth c. 2.8 Ga - Hydrothermal Delivery of Dissolved
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