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Lecture 6

Lecture 6

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Environmental Science
Nick Eyles

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 J ^Zoo on earth_- Rocks was molten, no water no atmosphere - Diversification J heavier elements sank to the middle - Magnetic field J to hold on to the gases J 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 J rock - Mineral rich water = changes to the shell - Uplift J by continental crusts coming together (plate tectonics) - Erosion J wear away rocks Ammolite J an organic gemstone Ammonite fossils J iridescent aragonite with trace elements (Fe, Mn, Al, Ba) Trace Fossils - Preserved tracks, trails, burrows (protectionfood), borings - Ichnology J study of trace fossils - Bioturbation J process of disturbing sediment Fossils as clues to ancient environments - Palaeocology J 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
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