Download Lab 4: Fossil Preservation

Lab 2B: Fossil Preservation
Geology 1402
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What we will cover today…
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Definition of a fossil
Limitations of the fossil record
Modes of preservation
Biochemical signatures and pseudofossils
Fossil classification
Symmetry
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The branch of geology that
studies fossils
• Paleontology
– Paleo- from the Greek palaios—ancient
– Ology- the study of
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What is a fossil?
• Remains or traces of organisms (plants,
animals, etc.)
• Preserved through natural processes
• Over 10,000 years old
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To be preserved—Two Things
• Hard parts (there are exceptions to this)
– Teeth
– Bones (endoskeletons)
– Shells (exoskeleton)
• Rapid burial (preserved from decay)
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Mud
Clay
Volcanic ash
Marine (ocean) sediments
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The fossil record is incomplete…
• Few organisms with soft parts are preserved
(jellyfish, insects and many plants)
• No organisms that decay before burial
• Shallow marine organisms are most likely
to be buried rapidly
• Note:
– We have about 250,000 fossil species
– Today around 4,000,000 species exist
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Which is more likely to become a
fossil?
• Fish
• Rabbit
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Modes of Preservation
(There is a slide on each.)
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Unaltered preservation
Replacement
Recrystallization
Permineralization
• Carbonization
• Indirect preservation
– Molds & casts
– Trace fossils
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To Petrify
• To turn into stone—several methods.
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Unaltered preservation
• Original material is preserved
– Frozen mammoths of Siberia (ice)
– The Ice Man in northern Italy (5,000 years old)
– Tigers and insects in tar pits (15,000 years old)
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Unaltered preservation (cont.)
• Original material is preserved
– Insects in amber (amber is…) (100 million
years old)
– Desiccation (drying out—becomes a mummy)
in desert areas (sloth found in volcanic vent—
35,000 years old)
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Recrystallization
• Change in crystal structure of minerals
• Detailed structure is lost
• For example: Calcite (rhombohedral crystal
form) can change to aragonite (cubic crystal
structure). (Both calcite and aragonite have
the same chemical formula.)
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Replacement
• Groundwater dissolves original material
molecule by molecule and replaces it with
another mineral. Great detail is preserved.
– Calcite shells dissolve or
– Woody parts of trees dissolve
– Quartz or pyrite deposited
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Permineralization
• Groundwater passes through porous
remains and
– original hard parts remain and
– additional mineral material deposited in the
pores.
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Carbonization
• Most common way soft parts are preserved
• High pressure and temperature after burial
drives off volatile substances (hydrogen,
oxygen, nitrogen) and leaves behind mostly
carbon.
• These are carbon films that preserve details
of original organism
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Indirect preservation
• Molds and Casts
– Groundwater dissolves buried shell material
and leaves a mold in the surrounding material
– The mold later becomes filled with sediment or
minerals and forms a cast—a replica of the
original shell
– Not good detail
– Example: Pompeii, Italy (79 A.D.)
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Indirect preservation
• Trace fossils—evidence that an organism
was there
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Tracks
Trails
Burrows
Coprolites (fossilized dung)
Gastroliths (stomach stones)—swallowed to
help digestion (dinosaurs and chickens)—pits
etched by stomach acid and piles of 100 stones
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Indirect preservation
• Biochemical signatures (a type of trace
fossil)
– Carbon and sulfur with isotopic ratios
indicating living organisms
– DNA in soils
– Complex organic molecules
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Oldest evidence of life…
• Biochemical signatures
• Carbon spheres with isotopic signatures of
living organisms—3.9 billion years old
(organic origin is being debated)
• Undisputed organic carbon 3.7 billion year
old rocks
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Pseudofossils
(fake fossils)
• Naturally occurring inorganic minerals or
rocks which are mistaken for true fossils.
– Manganese dendrites—mistaken for plant
fossils. Water moves through a fracture and
deposits pyrolucite (a dark mineral)
– Concretions (geodes)—mistaken for dinosaur
eggs
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Fossil classification
• Linnaean system—same used to classify
living organisms
• Uses morphologic (form) structure as basis
• Three Domains (Five kingdoms)
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Linnaean Classification
• Kingdom
• Phylum
– Subphylum
• Class
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Order
Family
Genus
species
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Linnaean Classification
• Species—
– Group of organisms
– Similar structure, function and development
– Able to produce fertile offspring (in nature)
• Examples of non-species:
– Mule (female horse and male donkey)
– Liger (tiger and lion—only happens in zoos)
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Linnaean Classification
• Refer to an organism by genus and species.
• Genus capitalized; species lower case; both
italics
• Example: Homo sapiens
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Symmetry of invertebrate fossils
• No backbone or spinal column
• Symmetry—orderly arrangement of parts in
relation to lines, planes or points
– Radial
– Bilateral
– No apparent symmetry
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Types of Symmetry
• Radial symmetry: repetition around an axis
– Round birthday cake and pizzas
– Starfish and echinoids
• Bilateral symmetry: duplicate parts on each
side of a plane (like people)
– Clams
– Snails
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Radial symmetry
Bilateral Symmetry
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No Symmetry
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Any questions?
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