FOSSIL ACTIVITY
Competency: Describe the characteristics of fossils that can be used for dating the age of rocks
and sediments.
Student Name: _________________________________________
Grade & Section: ______________________________________
Date: ___________________
Group No.: ______________
QUICK REFERENCE CARD
Read this info to evaluate your 9 fossil models:
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Trilobite: Lived 521–252 million years ago (Extinct). Distinct 3-lobed body. Very common.
Ammonite (Early): Lived 400–200 million years ago (Extinct). Simple spiral shell pattern.
Very common.
Ammonite (Late): Lived 145–66 million years ago (Extinct). Complex, wavy shell pattern.
Very common.
Crinoid Stem: Lived 485 million years ago to Present Day (Still alive). Looks like small
stacked rings.
Bivalve Shell: Lived 518 million years ago to Present Day (Still alive). Common
clam/mussel shell.
Cidarid (Echinoid): Lived 250 million years ago to Present Day (Still alive). Sea urchin
body/spine.
Petrified Wood: Lived 390 million years ago to Present Day. Found only on land.
Megalodon Tooth: Lived 23–3.6 million years ago (Extinct). Rare top predator tooth.
Fossil Fragment: Unknown age. Broken piece with no clear shape or features.
PART 1: FOSSIL CLASSIFICATION TABLE (20 Minutes)
Examine your 9 fossil models. Use the Reference Card above to complete the table and classify
each model into one of three categories:
1. Best Index Fossil (Short lifespan, distinct shape, abundant)
2. Poor Index Fossil (Lived for hundreds of millions of years / still alive)
3. Unusable (Broken / cannot be identified)
Fossil Name
1. Trilobite
2. Ammonite
(Early)
3. Ammonite (Late)
4. Crinoid Stem
5. Bivalve Shell
6. Cidarid
(Echinoid)
7. Petrified Wood
8. Megalodon Tooth
9. Fossil Fragment
Lifespan on
Earth
269 Million
Years
200 Million
Years
79 Million Years
485+ Million
Years (Alive)
518+ Million
Years (Alive)
250+ Million
Years (Alive)
390+ Million
Years (Alive)
19.4 Million
Years
Unknown
Is it distinct &
easily identified?
Yes
Yes
Yes
Yes
Yes
Yes
Partial
Yes
No
Category (Best Index, Poor
Index, or Unusable)
PART 2: SYNTHESIS QUESTIONS (10 Minutes)
1. Why are the Bivalve Shell and Crinoid Stem POOR index fossils for rock dating?
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2. Why can't scientists use the Fossil Fragment to date a rock layer?
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3. Based on your sorting, list the 3 MAIN characteristics a fossil must have to be used as an
Index Fossil:
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Trait 1: __________________________________________________________________________
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Trait 2: __________________________________________________________________________
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Trait 3: __________________________________________________________________________