ASM 104
Fall 2012
NAME:
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Lab 9: GEOLOGY, DATING, AND TAPHONOMY LAB
Introduction:
This lab covers the geological processes that are important in understanding the
context of human evolution. We use geology to help determine what environment
organisms lived in, how these environments changed through time, and the age of
fossils and tools. This lab also covers taphonomy, the study of the processes that affect
an animal’s carcass after it dies. It is important to understand how taphonomic
processes can influence the interpretation of the fossil record
Activity 1: Stratigraphy
This diagram represents an “outcrop”, a rocky exposure such as those seen on the
sides of cliffs. In outcrops, the BEDS (layers or strata) are the result of some previous
natural geological event or process, such as a flood or erosion. Over time, the
accumulation of these processes causes layers of sediment to pile up and form
sedimentary sequences. According to the Law of Superposition, the older strata are
deeper in the earth and the younger ones are closer to the surface. However, the
process of erosion can cause unconformities in which beds that are not in chronological
sequence can be in contact with one another. Note that Bed 3 is not continuous so that
Beds 2 and 4 are in contact with each other. We can still be sure that Bed 2 is younger
than Bed 3. Note that there are fossils (A,B,C,D) in the beds.
Answer the following questions about the diagram:
HINTS:
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A mix of silt, pebbles and other unsorted sediments are the result of flooding
Sandy sediment (and sandstone) often reflects an extended dry period
1. Which is older, Fossil B or Fossil C? ______________
2. Which bed (give the number) contains Fossil C?
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_________________
3. A volcano 100 miles from this fossil locality has erupted several times, each time
spewing ash for hundreds of miles. Which Bed or Beds formed during times of
volcanic activity?
4. Which fossil or fossils was/were deposited during a time of flooding?
5. Which is younger, Fossil A or Fossil C?
6. Which Bed probably formed during arid (dry) periods of time?
Activity 2: Stratigraphy
Sometimes geological layers that occur in one area are not seen at others. When
this happens, geologists develop a composite stratigraphy that shows the ordering of
all the layers across a large region. The guiding principle is the Law of Superposition,
and if one layer is above another layer in one location, that will be true everywhere.
1. Use the Law of Superposition and the four regional stratigraphies (Areas) to
create and label a composite stratigraphy in the space provided. Be sure to
label it with the type of stratum in case I can’t decipher your drawing!
Area 1
Area 2
Area 3
Area 4
Composite
Conglomerate
Sandstone
Silt
Basalt
Volcanic tuff
Limestone
2. Is stratigraphy a relative or absolute dating technique? Why?
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Activity 3: Dating
A. Most sites are dated first by biostratigraphy, or "faunal dating." The animal
species found at a site are compared to those at sites of known age in order to estimate
the age of the new site. At sites relevant to human evolution, pig fossils are very useful
for this purpose. The attached biostratigraphy handout (p. 6) gives you a phylogeny of
pigs and their time ranges for the last 6 million years. These dates are based on
absolute dating techniques.
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Using this information, place the following African sites in the correct order
through time (showing which is oldest to youngest). Each site has at least
two pig species present. The time of overlap for the pig species at each site
will give you a time range for that site.
First, record the total time range for each pig species:
Hadar South, Ethiopia
Tulu Bor, Kenya
Kolpochoerus afarensis
_____
Kolpochoerus limnetes ____
Notochoerus euilus
_____
Notochoerus eulius ______
Nyanzachoerus kanamensis ___
Notochoerus scotti ______
Time Range of Overlap: ______
Time Range of Overlap: ______
Hadar North, Ethiopia
Makapansgat, South Africa
Kolpochoerus limnetes _____
Notochoerus scotti _____
Phacochoerus modestus
Metridiochoerus andrewsi _____
______
Time Range of Overlap: ______
Time Range of Overlap: ______
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Second, determine the Time Range of Overlap of the pig species at each
site. This gives you an approximate age for each site.
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What is the order of sites (oldest to youngest) based on the Time Range of
Overlap?
1.
2.
3.
4.
B. One of the methods of absolute dating is Potassium-Argon dating. This method is
used to date rocks that have been heated to a very high temperature, such as those
that result from a volcanic eruption.
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In this composite stratigraphy, the solid black lines represent ashfall layers, or tuffs, that
have been dated using the K-Ar method. In between each tuff are geologic members,
in which many fossils have been found.
1. What date would you assign to a hominid skull that was found in the KBS Member?
2. Which is older, the Upper Burgi Member or the Chari Member?
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Activity 4: Taphonomy
Taphonomy is the study of what happens to an animal’s carcass after it dies.
Taphonomic processes such as predation or weathering leave characteristic marks on
bones which can be seen in the fossil record. During the long time period when skeletal
remains are becoming fossilized and before being collected by a paleontologist,
taphonomic processes will affect the remains. Each process may change the way the
fossils look or where they are located, so that they may no longer resemble their original
state when the animal died.
Fossils or Rocks?
Examine the specimens in Group 1. Can you tell which are fossils and which are not?
Fossils:
Taphonomic processes
Examine the specimens in Group 2. Each shows a pattern of damage or marks caused
by a specific taphonomic process.
· Match each of the following taphonomic processes to the specimen that displays
it:
Taphonomic process
Why? (What pattern on the bone indicates the process?)
______ Weathering
______ Predation
______ Abrasion
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Biochronology Handout
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