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ASM 104 NAME: ________________

Fall 2012

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

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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:

· 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? _________________

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!

2. Is stratigraphy a relative or absolute dating technique? Why?

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.

· 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: ______

· Second, determine the Time Range of Overlap of the pig species at each site. This gives you an approximate age for each site.

· 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.

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?

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

Volcanic tuff

Conglomerate

Silt

Basalt

Sandstone

Area 1 Area 2 Area 3 Area 4

Composite

Biochronology Handout

Limestone