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Geologic Time Scale & Fossils
Notes Part 1
Rock Types & Fossils
•There are 3 types of rock:
–Igneous, Sedimentary, and Metamorphic
–Sedimentary rocks often contain fossils
•Organic sedimentary rocks: “Once-living organisms” = fossils
Rock Layers
•The earth has distinct layers of
–The rock layers show a
progression of organisms from
layer to layer
–The oldest layer is on the bottom,
then each layer up is younger, with
the youngest layer being on the top
•This is because sediment is deposited on
top of previously existing sediment.
Relative Dating
•Relative dating can be used to estimate the
order of prehistoric and geologic events
•This happens by observing where fossils are
found in layers of rock
–The oldest rock layers contain the oldest fossils and
the youngest rock layers contain the youngest fossils
–A fossil must have existed at the time when the rock
layer was formed, which is how we can tell
Relative Dating
Timelines & Earth’s Age
•Timelines describe the timing and relationship
between events in the Earth’s history.
•Earth is estimated to be 4.5 billion years old
•A fossil is an imprint,
replacement, or remains of an
organism from ancient times.
•Fossils provide…
–a historical perspective on
change of the Earth.
–a biological record of life on
–a record of how organisms
have changed over time.
Fossil Record
• The fossil record can be aligned
to the major environmental
changes that have occurred on
•The fossil record provides
evidence from a “living laboratory.”
•The fossil record illustrates how
organisms responded to
environmental change.
–Some fossils provide a continuous record
of environmental change.