A Publication of the
Peoria Academy of Science Geology Section
P.O. Box 10294
Peoria, IL 61612-0294
Next Meeting:
Tuesday, January 26, 6:00p
Forest Park Nature Center
5809 Forest Park Drive
Peoria Heights, IL 61614
Program: Rock BINGO
Treats: Everyone (Potluck)
Please RSVP to Pam
Lapidary Shop:
The Lapidary Shop is open at
the Miller Center in Pekin
EVERY THURSDAY from 6
to 9pm, except during
holidays or when the Miller
Center closes due to weather.
Mineralogy Study Group:
Tuesday, January 12, 7:00p
Hosted by the Eggers at
307 Peach Street
Washington, IL 61571
309.745.3558
This Month’s Topic:
Energy & Material Flow
within the Earth
Meetings always begin
with a show-and-tell,
where we identify mystery
samples. Bring samples,
food, and/or drink to share!
Field Trip Brainstorming:
Both the Geology Section as
a whole and the Mineralogy
Study Group host field trips
throughout the year, and we
always welcome locations
or specimens to gather!
Please join us at one of our
events in January and
February to help us plan for
the new year, or e-mail
ideas to Matthew.
The January meeting at Forest Park Nature Center is our annual BINGO and potluck dinner.
The club provides the meat, but please bring a dish to share. This meeting starts at 6:00 -- an
hour earlier than the rest of the meetings. Bring several wrapped specimens or other “rocky type
things” for rock bingo after the feast! There will be no formal meeting, just a party -- members
will mingle and have a good time. This party is for members ONLY -- membership is required
and will be checked at the start of the event. New members are welcome (bring your friends and
workmates!), but they will need to complete the membership process. - Paul Dennis, President
In October we looked at the role of relative dating in learning from rocks: the law of
superposition states that the lowest layer of sedimentary rock is the oldest while intrusions,
tilting, and fault lines offer additional clues. While relative dating can only tell us if rock is
older or newer than surrounding formations, absolute dating uses techniques like radiometric
dating to get more exact ages of rock and archeological evidence.
Rocks naturally contain radioactive elements, including Uranium-238. Radioactive
elements break down into stable versions of other elements over time. The period of time in
which half of the radioactive element will have decayed is called its half-life. By measuring the
amount of a radioactive element compared to its more stable brother, scientists can determine a
pretty accurate age. (With materials that are often billions of years old, a margin of error in the
millions of years is more than acceptable!)
This method works best with igneous rock. Particles of sediment within sedimentary rock
can be accurately dated, but the time of compaction and cementation of the sedimentary rock is
often difficult to identify. Scientists typically combine absolute and relative dating methods in
order to gain an approximate age. Using radiometric dating with metamorphic rock is also
troublesome, as pre-existing minerals may be altered and new minerals formed. Depending how
the rock is metamorphosed, radiometric dating may or may not be possible.
Uranium-238 breaks down into Lead-206 with a half-life of 4.5 billion years, so if the ratio
of Uranium-238 to Lead-206 is 3:1 (1/4 of the material has decayed), the rock has an
approximate age of 2.25 billion years. If the ratio of Uranium-238 to Lead-206 is 1:1 (1/2 of the
material has decayed), the approximate age is 4.5 billion years.
Items which are living constantly regenerate a radioactive form of carbon (Carbon-14), but
when they die the Carbon-14 changes to Nitrogen-14 with a half-life of 5,730 years. Because
the half-life of Carbon-14 is much shorter, it can be more accurately dated than rock, but after
about 50,000 years it cannot be dated at all using this method.
See if you can complete the following table using the half-life of Carbon-14:
Parent
Daughter
P:D Ratio
# of HalfC-14
N-14
Lives
1
0
1:0
0
1/2
1/2
1:1
1
1/4
3/4
1:
1/8
1:7
1/12
3.5
15/16
Time
Elapsed
0 years
5,730 years
11,460 years
17,190 years
20,055 years
Banner Caption: A geode with quartz and capillary pyrite opened at the November meeting.
Answers from top-left to bottom-right:
1:3
2 half-lives
7/8
3 half-lives
11/12
1:11
1/16
1:15
4 half-lives 22,920 years
Club memberships expire in December, so it is time to renew yours! Renewal is $20 per family or $12 for a single person.
Checks should be made out to PAS Geology.
Please include your address, phone number, and e-mail to ensure our records are up-to-date, as well as the age of each family
member for insurance purposes.
Please mail your renewal to Pam (6003 N Heinz Ln. / Edwards, IL 61528) or bring renewals to the January meeting.
As a bonus for renewing your membership early, any member who pays their 2016 dues before the end of 2015 can save $5 on
the first apparel item ordered below. (Limit 1 item per individual membership or 2 items per family membership.)
Peori
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ademy of
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If we have enough interest, we plan to order some clothing embossed with the Peoria Academy of Science
Geology Section logo. They would be perfect for club field trips, events, and for representing the group
in public. Items will be available in either gray or safety orange.
To place an order, please e-mail or call Matthew Hagaman, newsletter editor. He will need to know
quantity, size(s), and color(s) as well as type (T-shirt, polo, or hoodie).
Geology Section
Geology Section
Embroidered Polo
$20
ademy of
Ac
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ienc
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Peori
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T-Shirt
$10
Geology Section
Hoodie
$20