The Rock and Fossil Record
1. Earth's Story
a) Uniformitarianism-__________________________________________________
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b) Catastrophism-_____________________________________________________
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Scientists now realize neither of these theories fully account for all of
Earth's history. Geologic change is gradual and uniform but catastrophes
can happen as well.
2. Relative Dating
a) relative dating-_____________________________________________________
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b) superposition-______________________________________________________
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c) geologic column- __________________________________________________
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3. Disturbing Forces
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Some rock layers are disturbed by forces from within the Earth, these
forces can push rocks out of sequence
d) fault-_____________________________________________________________
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e) intrusion-_________________________________________________________
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f) folding-___________________________________________________________
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g) tilting-____________________________________________________________
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4. Gaps in the Record
-missing rock layers can create gaps in rock-layer sequence
 unconformity-______________________________________________________
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Causes
 nondeposition-_______________________________________________
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erosion-_____________________________________________________
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Types
 disconformity-________________________________________________
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nonconformity-_______________________________________________
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angular conformity-____________________________________________
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5. Absolute Dating
 absolute dating-____________________________________________________
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 Element- a substance that cannot be separated into simpler components by
ordinary chemical means
 Atom- the smallest unit of an element that has all the properties of that element
 Atoms are made up of small particles called subatomic particles
 Electrons- negative electric charge
 Protons- positive electric charge
 Neutrons- no electric charge
 isotopes-__________________________________________________________
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o Most isotopes are stable, meaning they stay in their original form
however some isotopes are unstable
 radioactive isotopes-_________________________________________________
o Radioactive isotopes tend to break down into stable isotopes of other
elements
 radioactive decay-___________________________________________________
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 radiometric dating-__________________________________________________
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 half-life-___________________________________________________________
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o Every half-life, the amount of parent material decreases by one half
6. Fossils in Rocks
 Fossil-_____________________________________________________________
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o When organisms die, the soft, fleshy parts of their bodies decompose,
leaving only the hard parts
o Occasionally, these hard parts get buried quickly in sediment and are
preserved while the sediment turns to rock
o Organisms with hard body parts are more likely to become fossils than
those with only soft parts because they take longer to decompose
7. Mineral Replacement
 Permineralization-___________________________________________________
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 Petrification-_______________________________________________________
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8. Fossils in Amber
 Insects can be preserved in tree sap after getting stuck, the tree sap hardens
forming amber
9. Mummification
 When an organism dies in a dry place (desert) the can dry out so fast there isn't
enough time for their soft parts to decay
 These organisms don't decay because the bacteria that feed on them can't live
without water
10. Frozen Fossils
 Animals frozen between huge pieces of ice and preserved until the glacier melts
11. Fossils in Tar
 Animals that have been stuck in tar pits, die and fossils are formed
12. Trace Fossils-_____________________________________________________________
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 Animals left tracks in the ground, these tracks became fossils when they filled
with sediment that eventually turned to rock
 Burrows are another form of fossil, burrows are preserved when they fill in with
sediment and bury quickly
 Coprolites are preserved feces, they can give scientists information about the
diet and habits of ancient animals
13. Molds and Casts
 Mold-_____________________________________________________________
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 Cast-_____________________________________________________________
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14. Geologic Time Scale
 Scale that divides Earth's 4.6 billion year history into distinct intervals of time
 Eon-______________________________________________________________
 Era-_______________________________________________________________
 Period-____________________________________________________________
 Epoch-____________________________________________________________
o The boundaries between geologic time intervals represent major changes
on Earth.
o These changes include appearance or disappearance of life forms,
changes in global climate and changes in rock types
15. Eons
 Hadean Eon
i. 4.6-3.8 billion years ago
ii. Only rocks are meteorites and rocks from the moon
 Archean Eon
i. 3.8-2.5 billion years ago
ii. Formation of earliest known rocks
 Proterozoic Eon
i. 2.5 billion-540 million years ago
ii. First organisms with well developed cells appeared
 Phanerozoic Eon
i. 540 million years ago-present
ii. Rock and fossil record mainly represents this eon
16. The Paleozoic Era (540-248 million years ago)
 Beginning Middle End Came to an end with a mass extinction nearly 90% of all species died
17. The Mesozoic Era (248-65 million years ago)
 Age of the Reptiles
 Dinosaurs inhabited land and water
 Birds and small animals evolved late in the era
 By the end of the Mesozoic era, about 50% of all species on Earth, including
dinosaurs, became extinct
18. The Cenozoic Era (65 million years ago - present)
 Age of the Mammals
 After the mass extinction in the Mesozoic era, mammals became abundant on
Earth