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Worksheet
Chapter 12.1-12.3
Chapter 12.1 – The Fossil Record
MAIN IDEA: Fossils can form in several ways. In the spaces provided, write either the type of fossil being described or a
brief description of how the fossil type is formed.
Type of Fossil
Description of Fossil Formation
1. Amber preserved fossil
Organism trapped in tree resin that hardens after being buried.
2. Natural cast
An impression is left in sediment, and minerals fill the impression in,
recreating the original shape of the organism.
3. Trace fossil
Record of the activity of an organism, such as a nest or footprints
4. Permineralized fossil
Minerals are deposited around a hard structure and may replace the
structure
5. Preserved remains
Organism becomes encased in materials such as ice or volcanic ash, or
immersed in a bog.
Use Figure 12.2 in the textbook to fill in a sequence diagram that describes the process of permineralization.
Fill-in the graphic organizer with the appropriate terms, definition and examples (examine pages 360-363 in the
textbook to asset you):
12. What is the main purpose of both relative dating and radiometric dating?
Both relative dating and radiometric dating are used to determine the age of a fossil or rock layer
13. What is the main difference between relative dating and radiometric dating?
Relative dating is an estimate based on the fossil or rock layer’s location, whereas radiometric dating
determines a fossil’s absolute, or actual, age.
14. How is the radioactive decay of an element used to determine the age of a rock layer?
As an isotope of an element decays, it can transform into a different element. Because the decay rates of
many radioactive isotopes are known, the proportion between an original element and its product isotope
allows scientists to determine when that rock layer was formed
15. Look at the graph above illustrating the Half-life. Determine what percentage of carbon-14 remains in a sample after
two half-lives?
25%
Vocabulary Check
(A) Relative dating
(B) radiometric dating
(C) isotope
B
16. Measures the actual age of a fossil
C
17. Most elements have several of these
D
18. Measure of the release of radiation
A
19. Infers order in which groups of organisms existed
(D) half-life
Chapter 12.2 – The Geological Time Scale
MAIN IDEA: The geologic time scale divides Earth’s history based on major past events. Index fossils are another tool to
determine the age of rock layers.
1. How are index fossils used to determine the age of fossils or rock layers?
Index fossils are used as markers to identify a particular layer of rock wherever it is found.
2. What four characteristics are best for an index fossil to have?
1.
2. Easy to identify
3.
4. Existed for a relatively brief time.
The names of eras come from early ideas about life forms preserved as fossils. Provide the meaning of the following
names of eras:
3. Paleozoic
Ancient Life
4. Mesozoic
Middle Life
5. Cenozoic
Recent Life
6. How is the geologic time scale a representation of the history of Earth?
The geologic time scale organizes Earth’s history by major changes or events, using evidence from fossil and
geologic records.
Chapter 12.3– The Origin of Life
1. The origin of life still remains a puzzle. Earth was very different billions of years ago, however most scientists agree on
two points about Earth’s origins. What are they?
(1) Earth is billions of years old, and (2) the conditions of the early planet and its atmosphere were very
different from those of today.
Fill-in the Web with the descriptions of the early Earth atmosphere
Several sets of hypotheses propose how life began on Earth. Examine the table below, in the column on the left labeled
“hypothesis,” write the hypothesis from the readings about how life began on Earth. In the column labeled “proof,” list
the evidence that supports the hypothesis. Finally, answer the question at the end of the table.
Hypothesis
Proof
I. ORGANIC MOLECULE HYPOTHESES
9. Miller-Urey
Demonstrated organic compounds could be made by passing electrical
current (to simulate lightning) through a closed system that held a
mixture of gases (to simulate the early atmosphere).
10. Meteorite hypothesis
More than 90 amino acids have been identified from this meteorite
II. EARLY CELL STRUCTURE HYPOTHESES
11. Iron-sulfide bubbles
hypothesis
Simulated in the lab, making a chimney structure with compartments that
could have acted as the first cell membranes.
12. Lipid membrane
hypothesis
Spontaneously form in nature and could have formed the f irst true cell
membranes.
III. RNA AS EARLY GENETIC MATERIAL
13. RNA world hypothesis
Ribozymes are RNA that can catalyze their own reactions without the
additional enzymes that are needed for DNA replication.