Transcript Chapter 17 Section 1 The Fossil Record

The Fossil Record
http://www.npr.org/2012/05/06/15
2019967/the-dinosaurs-nemesesObjectives:
giant-jurassic-fleas
-Describe the fossil record
-State the information that relative dating and
radioactive dating provide about fossils
-Identify the divisions of the geologic time scale
17-1 The Fossil Record
I. Fossils and Ancient Life
A. _______________
Paleontologists are scientists who
study fossils.
B. The fossil record _________
provides evidence
about the history of life on Earth. It also
shows how different __________
groups of
_____________, including species,
organisms
have changed over time.
II. How Fossils Form
A. For a fossil to form, either the _________
remains of
___________
the
organism or some trace of its
presence must be preserved.
1. A precise _________________
set of conditions must be
present to form a fossil.
2. The fossil record provides ____________
incomplete
____________
information about the history of life.
sedimentary
B. Most fossils are formed in ___________
_______.
rock.
1. Sedimentary rock forms from the
_________________________________
erosion
of rock into sand, silt, and clay.
2. These particles are carried by _________
streams
___________
and rivers into lakes or seas, where
they eventually settle to the bottom.
3. As layers of sediment build up over time,
________________________________
dead organisms may also sink to the
bottom and become buried.
_______
4. If conditions are right, the ________
remains may be
kept intact and free from decay.
5. The sediment gradually _____________
compresses into
_______
rock.
Figure 17-2 Formation of a Fossil
Section 17-1
Water carries small rock
particles to lakes and seas.
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Section:
Dead organisms are buried by
layers of sediment, which forms
new rock.
The preserved remains may
later be discovered and
studied.
III. Interpreting Fossil Evidence
A. Paleontologists determine the ________
age of
_______
fossils using two techniques:
1. Relative Dating
a. The age of the fossil is determined by
______________________
comparing its placement with that of
fossils in other layers of rock.
nearer to the surface are
b. Rock layers __________________
generally ________
younger than those below it.
Relative Dating
c. Does not determine the ___________
actual ageof the
rocks or the fossils.
compare the
d. Index fossils are used to ____________
relative
age of fossils
___________________.
These fossils
must be easily recognized and must
have existed for a short period of time.
Relative dating allows paleontologists to estimate a fossil's
age compared with that of other fossils.
• Index fossils are used to compare the relative ages of fossils.
• An index fossil is a species that is recognizable and that existed for a
short period but had a wide geographic range.
Copyright Pearson Prentice Hall
2. Radioactive Dating
radioactive decay of
a. Based on the ___________________
___________________.
elements in the rocks
or break
b. Radioactive elements decay, ________
______,
downat a steady rate which is
measured in a unit called half-life.
c. Half-life: the length of time required
for __________________________
half of the radioactive atomsin a
sample to decay.
d. Different radioactive elements have
different half-lives and therefore provide
______________
natural clocks that “tick” at
______________.
different rates
Example:
5,730
Carbon-14:
half-life of about ______
years
________
1.26
Potassium-40 :
half-life of about ______
billion
years
___________
e. Carbon-14 is _________
taken up by living things while
they are alive
______________.
After an organism dies, the
Carbon-14
__________ in its body begins to decay to form
Nitrogen - 14, which escapes into the air.
short half-life
f. Carbon-14 has a relatively ____________,
it is useful only for dating fossils younger than
about ____________.
60,000 years
Carbon-14
Radioactive Decay
B. Most fossils are __________.
not intact Paleontologists
must reconstruct an extinct species from a few
fossil bits---remains of bone, a shell, leaves, or
pollen.
Compare/Contrast Table
Section 17-1
Comparing Relative and Absolute Dating of Fossils
Relative Dating
Absolute Dating
Can determine
Age of fossil with respect to
another rock or fossil (that is,
older or younger)
Age of a fossil in years
Is performed by
Comparing depth of a fossil’s
source stratum to the position of
a reference fossil or rock
Determining the relative
amounts of a radioactive isotope
and nonradioactive isotope in a
specimen
Drawbacks
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Section:
Imprecision and limitations of age Difficulty of radioassay
data
laboratory methods
IV. Geologic Time Scale
A. Scientists first developed the _________
geologic
_____________
by studying rock layers and
time scale
index fossils worldwide. As geologists studied
the fossil record, they found _______
________
major changes
in the fossil animals and plants
_________________________.
These times
at specific layers in the rock
were used to mark the segments.
Continental Drift
Plate Boundaries
San Andreas Fault
Big Chino Fault