Name: ___________________________ Period: ____________________ Date: _____________
GUIDED NOTES
Fossils and the Rock Record
The Rock Record
 Rocks record ________________________ events and changing life forms of the past
 Planet Earth was formed ________________________ years ago
 Earth’s surface and interior have been ________________________ by the same geological
processes throughout Earth’s history
Why study fossils?
 Fossils are ________________________ remains, imprints, or traces of once living organisms
which are preserved in rocks.
 We can piece together ________________________ puzzles of the past by studying fossils
 Almost all fossils are found in ________________________ rock!!!
WHY?
 To become a fossil, a dead body must be________________________ from scavengers and
microorganisms
– Sediments can cover and ________________________ a dead organism
– Sediments protect dead organisms from being ________________________ by other
animals
– May also slow down or stop the ________________________ process
 Usually fossils are the ________________________ parts of organisms, such as: bones, shells,
and teeth
– This is because these parts ________________________ better
 Ways to Become a Fossil
 ________________________ main ways
– ________________________ - remains have not been changed much over time
 Mummification
– ________________________ remains- remains are changed over time
 Carbonization
 Mold & Cast
 Petrification
Petrification
 Petrified remains are hard and ________________________
 The original material is ________________________ with minerals.
 Commonly Petrified Objects…
– ________________________
– Bones
Carbonization
 When lots of sediments build up, the body deteriorates and is left as only a thin film of
________________________residue.
 Residue forms an outline of the organism, a fossil ________________________. This can be of
fish or plants.
 This kind of fossil is called a ________________________ film.
Molds & Casts
 Air and water reach something ________________________ in sediments and decay it
 It will leave behind an ________________________space in the rock called a mold
 Later other sediments fill in the cavity and ________________________
 This produces a ________________________ of the original object
________________________ Remains
 Sometimes actual remains may be found ________________________ in some way
– Amber- Hardened tree sap
– Frozen ________________________
– Ice
– Tar pits
– Mummification
Drying
 Often found in ________________________ caves or buried beneath the desert sand
 Most ________________________ cannot survive without water, no waterorganism does not
decay!
Other Fossil Evidence
 Trace fossils – evidence of ________________________ activity
– Tracks
– Burrows
 Tell us about the ________________________ of the animals.
Index Fossils
 From species that were on Earth for a ________________________ amount of time but were
abundant
 Fossils used to determine ________________________ of rock layers
 Fossils can also be used to determine ________________________ environmental conditions
 If a scientist found the same index fossil in two different areas of the world this indicates the
________________________ were made at the same time
Relative Dating
 Used to determine ________________________of events and the relative age of rocks by their
position in a sequence.
 Doesn’t tell you the ________________________age
 Tells you age in ________________________to other rocks
 ________________________in the rock record are called unconformities.
 Telling the ________________________age of rock beds
 Law of Superposition- In an undisturbed layer of rock, the ________________________ rocks
are on the bottom and the rocks become progressively younger toward the top.
 Principle of original horizontality-layers of sediment are generally ________________________
in a horizontal position
 Principle of cross cutting relationships- states that if a rock layer cuts through another the layer
that cuts through must be ________________________ than the layer it cuts
Unconformities-________________________ in the rock record
 Angular Unconformity –Horizontal layers are tilted and lifted ________________________
 Disconformity -A ________________________ in the record caused by rocks being exposed and
eroded. How it works?
 Sediment was deposited then eroded and new sediment was ________________________ on
top leaving a gap in the record.
 Nonconformity –sedimentary rock forms above another rock type (igneous or metamorphic).
The other rocks are ________________________ and eroded.
Absolute Dating
 Method used by geologists to determine ________________________, in years, of a rock or
other object.
 Uses the ________________________in rocks and other objects.
Radioactive Decay
 Radioactivity-________________________decay of the nuclei of unstable atoms
 When the number of neurons in an atom change, it becomes a new
________________________
 ________________________Life
 Time it takes for ________________________the atoms in the isotope to decay
 Ex: Carbon-14 has a half-life of ________________________
– Every 5730 half of the C-14 will decay into N-14
 When C-14 decays into N-14, C-14 is considered to be the parent material and N-14 is the
daughter product
 C-14 can be used to date objects up to 70,000 years
 By measuring the amounts of parent & daughter material, ________________________ can
calculate the age of a rock.
 This is called ________________________dating
Radiocarbon Dating
 Carbon 14 can be used to date fossils, bones, and wood as old as
________________________Organisms take carbon to build tissues and once they die, it decays
away
 Used mostly for igneous and metamorphic rocks…can not be used for sedimentary rocks
Uniformitarianism
 Principle that states that the ________________________ occurring today are similar to the
processes from the past.
 Used this theory to argue ________________________ those who thought the Earth had only
been around for a few thousand years.