To answer the question, “Why are mammoth bones found in northern Illinois?” one simply needs to look at the geologic cross sections in the area. Relative dating shows that a sequence of environments were present in the area before the grasslands and wetlands we are used to today. The cross section of the Mud Lake site displays what once was a swampy environment that came after a site that was near the terminus of a retreating glacier. This shows climate in the area was once much different than what we are used to today.

Putting an actual date on these bones found places this environment roughly 14,000 years ago. Knowing the average decay rate of C14 helped geologists place a numerical date on these mammoth bones.

It was previously thought that human ancestors did not occupy the area until 13,000 years ago. Relative dating and absolute dating practices have now moved this date back an extra 1,000 years. Markings on the bones shows these animals were butchered by recent human ancestors. This helps place a landmark with a date for the evolution and migration of Homo sapians living in North America during the Pleistocene.

Had Maine East been located in the area nearly 10,000 years ago, we may have changed from Demon Pride to Mammoth Pride.

Relative Dating

Absolute Dating

Discussion

References

Abstract / Background Information

Belew, B (2009). Evolution 101: What are the problems with Carbon-14 Dating? Retrieved March 10, 2010, from http://www.examiner.com/x-4865-Christian-Worldview-Examiner~y2009m8d14-Evolution-101-What-are-the-problems-with-Carbon14-dating.

Friends of the Ice Age. (2004) Butterbroad, J. woollymammoth.org. Retrieved February 21, 2010, from http://www.woollymammoth.org/.

Tarbuck, E. J. & Lutgens, F. K. (2005). Earth: an introduction to physical geology, 8th ed. Pearson Education, Inc., Upper Saddle River, New Jersey.

Wisconsin Geological and History Survey. (2009). Bedrock Geology of Wisconsin [Map]. Retrieved February 23, 2010, from http://www.uwex.edu/wgnhs/bdrk.htm

Woolly Mammoth (2009). Illinois State Geologic Survey. Retrieved February 22, 2010, from http://www.isgs.illinois.edu/education/ice-age-res/mammoth.shtml.

Radioactivity – Spontaneous Decay of unstable isotopes

Half Lives:

Figure 5. Samples were taken from this lower leg bone from a mammoth found in Kenosha, WI for C14 dating (FIA, 2004).

Conclusions

Mammoths?Mrs. Awad, Mr.

Baldwin & Mr. Bihn

If Our School Was Here Over 10,000 Years Ago, What Would Our Mascot Be?

Figure 6. Overhead picture of the Mud Lake excavation site where leg bones were removed during a construction project (FIA, 2004).

Atomic Number

Decreases by 2

(lost 2 p+)

Increases by 1 (no

changes to a p+)

Decreases by 1 (p+

changes to a no)

Atomic Mass

Decreases by 4

(lost 2 p+ & 2 no)

Stays the same

(looses an e-)

Stays the same

(gains an e-)

Radiometric Isotope Concentrations

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6

Half Lives

Per

cen

t Is

oto

pe

Rem

ain

ing

Parent Remaining

Daughter Remaining

Number of years for ½ of the original number of atoms to decay from the parent isotope to the daughter isotope. Knowing the ratio of parent to daughter can help determine the age of the sample.

Figure 3. Parent Daughter isotope curves plotted over several half lives. The percent parent plus the daughter always equals 100.

    

The rocks on the left are original, some force created

the rocks to the right.

The rocks on top are younger than the rocks on the bottom

Angular UnconformityAngles between

sedimentary rock layers

DisconformityAge gap between

horizontal sed layers

Nonconformity

Sed rock layers over meta or ig

rocks

Figure 1. Pathway of unstable parent isotope U238 to daughter isotope Pb206 following steps of alpha and beta emissions (Tarbuck & Lutgens, 2005).

Figure 2. Three types of decay as seen on the atomic level (Tarbuck & Lutgens, 2005).

*Unless noted, all pictures from class handouts

Bones of mammoths with odd marks on them have been found in northern Illinois and southern Wisconsin. Illinois is not the typical habitat of large elephant-like animals, so why do we find mammoth bones in Illinois and what are these strange lacerations on them?

In 1936, work crews channelizing the outflow creek from Mud Lake encountered roughly 20 leg and foot bones of a Woolly Mammoth. These bones represent what scientists believe to be butchered remains of Woolly Mammoths that place Paleoindians in the area 1,000 years before originally thought (FIA, 2004).

Relative dating have placed these bones in a sequence of events that shows these animals lived relative recently in relation to soil and rock layers beneath them. Absolute dating techniques have been used to put an actual date on them as well. Geologic practices have helped tell the story of why mammoths are found in northern Illinois.

Mammoth fossils found in the area were from the

Pliestocene Epoch of the Quaternary Period

Cross-Cutting RelationshipAn intrusion that cuts across sedimentary layers must be

younger than those sedimentary layers.

Law of Superposition

Law of Original Horizontality

In Relative Dating:- Rocks are placed in their proper sequence of formation (i.e. which formed 1st, 2nd, 3rd, etc.- We have no idea of the age of the rocks, simply which were deposited in which order.

Figure 4. Living organisms, such as mammoths, constantly cycle C14 until they die (Belew, 2009)

The mammoths found in northern Illinois were dated found to be 14,470 years old (FIA, 2004). Carbon-14 dating was used to determine this age. The half-life of C14 is 5,730 years (Tarbuck & Lutgens, 2005). Using the graph in Figure 3, we can determine that after 14,470 years, C14 would decay, through beta decay, roughly 2.53 half-lives. At the time the bones were excavated (Figure 5), there was: - 34.75% of the original C14

- 65.25% changed to N14 through beta decay

Clay Layer

Peat

Dolomitic Limestone

Glacial Till

The law of superposition states the layer of peat is the youngest while the layer of Dolomitic Limestone is the oldest because the peat horizon is on the top (Figure 7). These layers remain relatively horizontal, since there has been little tectonic activity in this portion of the country over geologic time.

Geologists were able to decide how deep to dig based on layers found at other sites (Figure 6).

Figure 7. Mock cross section of the layers found in the Mud Lake excavation site in Kenosha, WI (drawing not to scale).

-Swampy Environment-Terminal glacial deposits with low energy water present-Melting glacier deposits-Shallow ocean with CaCO3 precipitation

Depositional Environment