Fossils are
the remains or impression of a
prehistoric organism preserved in
petrified form or as a mold or cast in
rock.
HOW DO FOSSILS FORM?
• The formation of any fossil is
a rare event
• Most fossils form when
organisms die and are buried
Determining a fossils age
• TWO WAYS
relative and radioactive dating
What do fossils reveal?
Millions of fossils scientists have collected is
called the FOSSIL RECORD
FALSE: The fossil record is complete.
Why? Sediment has to cover an organism's
remains in order for the long fossilization
process to begin. Most organisms decompose
before this can happen.
EXTINCTION: is when all members of a certain
species die.
Major evolutionary events
APPROXIMATE DATE
540 mya
EVENT
Life in shallow seas started
fish evolved
430 mya
410 mya
Life on land formed
GEOLOGIC time scale
How FAST does evolution occur?
Gradualism: the idea that change can take place
through the cumulative effort of slow but
continuous processes
Why is this theory questioned? If this is correct,
then the fossil record should contain many fossils
with forms intermediate between different species.
This is not what the fossil record shows.
Punctuated equilibria: a lot of evolutionary change
takes place in short periods of time and that most
species will exhibit little evolutionary change for
most of their geological history
Vocabulary
Fossil: the remains or impression of a prehistoric
organism preserved in petrified form or as a mold or cast
in rock.
Extinct: all members of a certain species have died
Geologic Time Scale: is a system of chronological
measurement that relates to time, and is used to describe
the timing and relationships between events that have
occurred throughout Earth's history.