An Archaeologist’s Guide to Dating (the Past): Part 2: Absolute Dating

This post is a continuation of the previous post (insert link) that focused on relative dating, and today’s post is going to focus on absolute dating, which provides us with a more specific, precise date of sites, objects, artifacts, and fossils.  Absolute dating techniques are usually chemically based in practice, meaning archaeologists have to conduct chemical and physical tests on the artifacts or objects in order to get that date.  So much like real life dating, you have to have the right chemistry to get that date. 

There are many absolute dating techniques because they provide us with that more precise date, which is ultimately what we want in archaeology, but I want to highlight the most common: radiocarbon dating and dendrochronology. 

Radiocarbon dating, also known as Carbon-14 dating, is a radiometric technique using the decay rate of a radioactive isotope of carbon found in organic remains (e.g. bone, hide, antler, plant remains).  This method utilizes the amount of carbon 14, an unstable isotope, left in an object as compared to carbon 12, a stable isotope, to determine the age of an artifact.  Carbon 14 is abundant in the atmosphere and readily absorbed by organic matter, particularly plants.  Plants use carbon dioxide in respiration (the process in which plants breathe and survive), and through this process, plants absorb carbon 14 as readily as stable carbon 12 elements.  Other organisms, including humans, absorb carbon 14 from eating plants or animals that ate plants.  While plants and animals, including humans, are alive, carbon is readily absorbed and lost, but after death, the carbon is no longer absorbed but it continues to be lost (Figure 1).  The carbon 14 present in organic remains continues to be lost after death through a process known as a half life, which is the amount of time it takes for half of an unstable isotope to disappear (by becoming a more stable isotope).  Scholars have a technique for measuring how much carbon 14 and carbon 12 should be in a body versus the known half life, and it is know that the half life of carbon-14 is 5,730 years (in which time it becomes a more stable nitrogen isotope).  Knowing this and measuring the amount of carbon 14 in an object allows one to date an object as long as the date is no more than 40,000 years old. 

Figure 1: The Carbon Cycle

Now this method has one serious limitation.  It is environmentally sensitive as the amount of carbon isotopes in the environment has varied over time.  The amounts of carbon in the atmosphere does vary for a variety of reasons, so the amounts of carbon that can and will be absorbed by organic materials will vary over time.  As such, dates derived over a long period of time can be skewed due to this environmental factor.  Scholars have utilized another absolute dating technique, dendrochronology, to get around this problem.

Figure 2: Tree Rings

 Dendrochronology is a dating technique that utilizes tree-ring sequences.  We know that each year a tree is alive it puts down what is known as a growth ring (Figure 2).  These tree rings provide scholars insights into the environmental conditions that the tree has been exposed to as large rings demonstrate times of plenty and narrow rings demonstrate poor conditions.  We also know that all trees in a given area will have similar tree ring sequences based on environmental conditions, although the ages will vary.  As such, scholars can get tree ring cores (Figure 3) from only a few trees in order to produce what is known as a master sequence, which is a general and relatively consistent pattern of tree-ring width variation over time within a given region.  This master sequence is created as a means of dating wood at sites. 

Figure 3: Tree Ring Cores

Once ages have been established for trees based on the master sequence and number of rings associated with the tree, the tree can be radiocarbon dated as a means of compensating for the environmental sensitivity limitations of radiocarbon dating.  This is a means of producing a calibration curve.  This calibration curve is produced by radiocarbon dating the tree with a known age and comparing the dendrochronological age and the radiocarbon date for consistencies and inconsistencies.    If the dates are consistent, then the radiocarbon date is unaffected by the environment and therefore is a reliable date, but if the dates are inconsistent, then a calibrated date that accounts for the difference between the two dates is attached to the radiocarbon dates derived from artifacts found in that region.  

Figure 4: Tree Ring Example

To put this in perspective, look at Figure 4, which depicts a tree that is approximately 550 years old based on its rings.  If we radiocarbon date this tree and that date is the same, then we know that the radiocarbon date is spot on and there is no environmental sensitivity issues.  If we, however, get a date that states that the tree is 700 years old, then we know that the date is 150 years off and any object-such as a bone tool-dated to 700 years ago with radiocarbon dating will have to have a date designation of 700 years +/-150 years because the tree date and the radiometric date are in conflict. 

This concludes the two part series focusing on archaeological dating techniques.  It is important to note that there are several different relative and absolute dating methods out there available to archaeologists for dating artifacts, objects, fossils, and the sites themselves.  These methods, however, are not discussed herein due to their uncommon use in the discipline for a variety of reasons.  You will most likely hear about these methods in your archaeological pursuits-be it in learning from professionals or hearing about them in popular culture pieces.  This information has hopefully provided you a little more detail into this matter and you have a better understanding of archaeological practice.

Reference:

Feder, Kenneth and Park M. Human Antiquity: An Introduction to Physical Anthropology and Archeology, McGraw-Hill.

Guest Post: Hominid Profiles

The following is a guest post by a former students, Destiny Fite & Tammy Winters, whose exemplary work on hominids warranted publication.  This post is being published now as both students opted to focus on their studies and school work and returned their edited paper after the end of term.  A prudent decision on their parts.  I hope this informative review on hominids provides you, the readers, with plenty of food for thought.

Neanderthal

Homo neandertalensis

By: Destiny Fite 

The Homo neandertalensis, or Neandertals, are generally considered the closest archaic relative and subspecies to Homo sapiens sharing physical, intellectual, and cultural similarities. Although the Homo neandertalensis is an entirely different species than Homo sapiens, both species evolved from the same common ancestor. The now extinct Neandertals inhabited geographic areas of Europe and Asia until the species disappeared nearly 28,000 years ago without any concrete explanations. While little is known about their disappearance, the fossil and cultural evidence collected from the Homo neandertalensis species provides insight into Homo sapiens closest known relative. 

According to the National Museum of Natural History, the Neandertals inhabited geographic areas of Europe and southwestern to central Asia approximately 200,000 to 28,000 years ago evolving from the same common ancestor as Homo sapiens. According to the text Introduction to Human evolution and Prehistory, the first Neandertal fossil was discovered in Neander Valley, Germany in 1856, thus giving the species the scientific name Homo neandertalensis. Present day, “nearly 400 Neandertal individuals…have been collected” with fossils distributed across “western Asia, including Israel, Iraq, Russia and Uzbekistan” (339). 

The analysis of the skeletal remains collected in the last 200 years provides a detailed profile of the anatomy and physical appearances of the common Neandertal male and female. The Homo neandertalensis species may have evolved from the Homo heidelbergensis because they share more similar physical characteristics than other species. The anatomy of the Homo neandertalensis reveals that this species was well adapted to colder climates having robust bodies with signs of heavier musculature attachments. The average male stood about five feet tall with an average weight of 143 lbs. Males were generally taller and heavier than the female but the comparison of Neandertal skeletal remains yields very little sexual dimorphism (Homo neanderthalensis). According to the text Introduction of Human Evolution and Prehistory, the skull also has distinctive features different from other hominid species characterized by a large and wide nasal opening, large orbits and pronounced brow ridges, low and flat cranium, occipital bun, and a projecting jaw. The Neandertal posture was once believed to be hunched over similar to the posture of an ape due to an incorrect analysis of a nearly complete skeleton excavated in La-Chapelle-aux-Saints, France in 1908. A reanalysis of the skeleton revealed the 40 year old man actually had severe arthritis in his spine. Although the classic cave-man hunched posture is still portrayed, the Homo neandertalensis species was completely bipedal just like the modern human (Dr. O’Neil, Dennis). In fact, the Neandertals were similar to Homo sapiens in physical appearance, intelligence, and even culture. 

Neandertal cultural evidence shows that the species made and used a variety of tools known as the Mousterian tradition “characterized by an increase in the number and variety of flake tools and an ultimate deemphisis of the hand axe” (Rowe, Bruce M). Excavations have surfaced nearly 20 different types of tools serving many different purposes. The Neandertals were skilled hunters of larger animals and various tools appear to assist in hunting and slicing meat. Other tools appear to be useful toward scraping hides and cutting wood as a means of building both fire and shelter.

Archeologists have also found numerous Neandertal skeletons that appear to be buried deliberately. Evidence reveals that the species placed specimens and artifacts such as flowers upon the graves suggesting ritualistic burials (Origins of Humankind). The Neandertals were more similar to modern humans in appearance and culture than previously assumed. Comparisons of skeletal remains reveal significant physical differences; however, according to the article, “Neanderthal-human Hybrids” written by Paul H. Mason and Roger V. Short, genetic evidence of Neandertal nuclear DNA in modern living humans suggests that the two species may have interbred as the Homo sapiens migrated out of Africa into Europe. This theory is highly debatable because there is not enough concrete evidence to prove interbreeding; however, genetic studies have extracted Neandertal nuclear DNA from nearly every modern ethnic race aside from the African race (Than, Ker). Genetic evidence does imply “only Neanderthal males were only able to mate with female humans” and “produce fertile offspring” due to the lack of Neandertal mitochondrial DNA (Mason, Paul H and Short, Roger V). It is also a possibility that any viable offspring produced by female Neandertals and male humans became extinct along with the rest of the species.

There are several theories regarding the mysterious disappearance of the Homo neandertalensis species. According to the Dr. Dennis O’Neil in the Behavioral Sciences Department at Palomar College in San Marcos, California, some theorists believe that the rapid growth and migration of more evolved and technologically advanced species such as the Homo sapiens caused the Neandertals to become extinct. Others assume that their extinction is connected to the “coldest phase of the last ice age” because the species did not “develop adequate technology for severe cold winter conditions” (Dr. O’Neil). However, there is not enough concrete evidence in either theory to prove cause of extinction. The lack of information regarding their disappearance does not displace the fossil and cultural evidence collected from the Homo neandertalensis species providing insight on the Homo sapiens closest known relative.

 Works Cited

Homo neanderthalensis. Smithsonian Institution. National Museum of Natural History. Web. 18 Apr 2014. <www.humanorigins.si.edu>

Rowe, Bruce M. Chapter 14. Introduction to Human Evolution and Prehistory. By Philip L. Stein. McGraw-Hill Education, 2014. Pg 344. Print.

Origins of Humankind. WGBH Educational Foundation. 2001. Web. 18 Apr 2014. <www.pbs.org>

O’Neil, Dr. Dennis. Analysis of Early Hominins. Retrieved from Behavioral Sciences Department of Palomar College, San Marcos, California. Web. 06 Apr 2014.

< http://anthro.palomar.edu/hominid>

Mason, Paul H., Short, Roger V. Neanderthal-human Hybrids. Hypothesis, 2011. Vol. 9.1 Web. 14 Apr 2014. <hypothesisjournal.com>

Than, Ker. Neanderthals, Humans Interbred—First Solid DNA Evidence. National Geographic Society News. National Geographic Society. 06 May 2010. Web. 14 Apr 2014. <.news.nationalgeographic.com>

 

Australopithecus sebida

 Australopithecus sediba

By: Tammy Winters

Australopithecus sediba is an ancient hominid species. This essay will compare the morphological features that define this species as an Australopithecine. I will compare these morphological qualities to those of the Homo species and indicate whether it should or should not be categorized as a member of the Homo species. As there is still much debate on the taxonomic naming of this species I will provide evidence supporting both sides of this argument. Lastly, I will conclude my opinion if Australopithecus sediba is indeed an ancient relative to the modern human species or if it should remain as a Australopithecine. Could this species be the “missing link?”

The recent find of paleoanthropologist Lee Berger of the University of the Witwatersrand in 2008 presented hominid fossils dating to 1.98 million years ago. The hominid fossil remains of Australopithecus sidiba were found in a limestone cave of Malapa, South Africa. The fossils show a mixture of morphological evidence of Australopithecus and the Homo species
A change in brain capacity from 400 cubic centimeters approximately 850 cubic centimeters is what suggests the morphological change from the Australopithecine species to Homo species. Australopithecus sediba has a brain capacity of 420 cubic centimeters categorizing it as an Australopithecine, but the shape and expanded regions of the frontal lobe suggest Homo qualities. Dr. Kristian Carlson conducted a study on the shape and formation of the fossil remains of a juvenile male. Results from the endocasts of the juvenile Australopithecus sediba indicated orbital frontal shape and organization that align more closely with modern human endocasts. The finding suggests that brain reorganization came before the change in brain size. This find may indicate a higher level of understanding and could possibly categorize the species as Homo if there were proven methods of tool use. This is still speculated as no tools have been found at the site.

The well preserved upper limbs of Australopithecus sediba suggest climbing and suspensory ability evidenced by predominantly primitive features. such as the shortened clavicle and bowed ulnar These features are more closely related to the chimpanzee, suggesting an arboreal adaptation. A nearly complete hand and wrist were found and indicate Australopithecus sediba had the use of precision grip and the ability to manipulate tools. This discovery gives the fossils Homo qualities , but the shortened clavicle indicates more primate like morphology. It is suggested that the climbing ability may have been due to the habitat of a rocky terrain and the need to climb this terrain the obtain shelter in caves. The legs and feet show that Australopithecus sediba used bipedal locomotion with a previously unknown method of upright walking. They also show combined traits of arboreality which may indicate the transition from arboreal to bipedal locomotion. Fragments of the vertebral column were found and all four sections of the spine are represented. Australopithecus sediba has the same number of vertebra as modern humans, including a flexible lower spine. Australopithecus sediba likely possessed five non-rib-bearing lumbar and five sacral elements resulting in a functionally longer lower back and indicating lordotic posture similar to the spine of Homo erectus. A broader lower chest and wider pelvic girdle are also found in the species. It is suggested these features may have evolved before other features in Homo.

Due to the mosaic of features present in Australopithecus sediba it is still being debated on whether it should be categorized as the species Homo or Australopithecus. The scientist who discovered Australopithecus sediba believes it should be categorized in the genus Homo because the broader pelvis, lower limbs, and dentition are more human like. Co-author of the project, Steven Churchill and his colleagues believe Australopithecus africanus gave rise to Australopithecus sediba which is suspected to evolve into Homo erectus. They also believe some of the Australopithecine species such as Homo rudolfensis more likely fall in the genus of Australopithecus.

Critics of this find believe Australopithecus sediba presents more ape-like morphology due to the appearance of the feet and ankle bones as well as the long arm length. They also believe Australopithecus sediba may be a subspecies of Australopithecus afticanus. Professor Lee Berger disputes this accusation because of post cranial and dentition differences between the two species.

In conclusion the mosaic skeletal remains of Australopithecus sediba makes classifying this species difficult. The debate on whether or not Australopithecus sediba is indeed an Australopithecine and not an ancestor of Homo still continues. Certainly the brain capacity of Australopithecus sediba give this species Australopithecine qualities, however the frontal lobe changes make it more Homo like. The transition for arboreal locomotion to bipedal locomotion is evident in this species, as well. The increase size of the ilium in the pelvic girdle and precision grip of the hands also align Australopithecus sediba with the Homo genus. While still not convinced Australopithecus sediba is the “missing link,” I do side with the founder of the species that it indeed has relevant Homo qualities and could potentially be deemed even another species falling between Australopithecine and Homo.



Works Cited

Barras, Colin. "Human 'missing Link' Fossils May Be Jumble of Species." Human 'missing Link' Fossils May Be Jumble of Species. New Scientist, 09 Apr. 2014. Web. 16 Apr. 2014.

Berger, Lee R. "Go to Science." Science Magazine: Sign In. Science Mag.org, 09 Apr. 2010. Web. 16 Apr. 2014.

Carlson, Kristain J. "The Endocast of MH1, Australopithecus Sediba." The Endocast of MH1, Australopithecus Sediba. Science Mag.org, 8 Sept. 2011. Web. 16 Apr. 2014.

Churchill, Steven E. "The Upper Limb of Australopithecus Sediba." The Upper Limb of Australopithecus Sediba. Science Mag.org, 12 Apr. 2013. Web. 16 Apr. 2014.

Switek, Brian. "New Studies Shake Up Human Family Tree." News.nationalgeographic.com. National Geographic News, 04 Apr. 2013. Web. 15 Apr. 2014.

Wayman, Erin. "Fossil Finds Complicate Search for Human Ancestor." Smithsonian. SMITHSONIANMAG.COM, 09 Sept. 2011. Web. 16 Apr. 2014.

Williams, Scott A. "The Vertebral Column of Australopithecus Sediba." The Vertebral Column of Australopithecus Sediba. Science Mag.org, 12 Apr. 2013. Web. 16 Apr. 2014.

Applied Anthropology Profile: Lauren*

Today’s post is part of a series of posts that focus on anthropologists working within the applied anthropology subdiscipline.  Applied anthropology is the application of anthropological theory and methods to identify and solve real life problems and situations that anthropologists confront within the course of their work.  This post spotlights the work of a former anthropology student, Lauren*, who utilizes her anthropology degree in pursuit of her law degree.  This story is not a traditional applied anthropology story but one that still fits theme of these posts.  Thank you, Lauren, for sharing your story with me and allowing me the opportunity to share it with my readers. 

Source: Google Images

 Lauren, like many individuals who become anthropology majors, did not start out wanting to an anthropologist.  She actually started as a psychology major, but the strictly empirical approach of the discipline did not appeal to her.  The holistic, broad spectrum approach provided by anthropological studies did, however, and she was inspired to major in anthropology in part by the anthropological approach to studying people as well as by an enthusiastic professor.  She eventually graduated with a bachelor’s in anthropology, and her first anthropology job was in cultural resource management (CRM) archaeology.  CRM archaeology is an applied subfield of anthropology in which archaeologists work to preserve sites and heritage resources within the private sector based on the laws and codes set up by local, municipal, provincial, state, and federal laws.  It was through this employment, particularly one project that involved close community collaborations with local indigenous groups, that Lauren was first inspired to do something more with her anthropology degree.  She wanted to go beyond the scope of her job and truly help the individuals she was working with, but she was limited by the laws and her degree.    

Lauren went to graduate school for her MA in Cultural Anthropology, and her MA thesis focused on refugee claims within the Canadian immigration system.  She was specifically interested in understanding refugee claims and why specific claims were denied while similar ones were approved by Canada’s Immigration and Refugee Board.  Lauren’s MA research remains incomplete at this time because she soon discovered that she was ill equipped with just her anthropological training to delve deeply into the problem and come up with a viable solution because she did not understand the intricacies of Canadian immigration law.  From here, coupled with her previous CRM experience and personal activism interests and spirit, Lauren decided to enter into law school in order to better assist in solving the problems she had identified as an anthropologist.

Lauren has found her anthropological education and background invaluable to her retraining as a lawyer.  Specifically, she identifies how her anthropological background has assisted her in realizing and recognizing that the Canadian legal system (and all modern legal systems) is a cultural construct that reflects the values and norms of the dominant culture and, as such, she recognizes that the law can be changed to better assist all citizens.  Cultural relativism is instrumental in understanding her clients’ needs, particularly in regards to refugee claims, and how certain legal decisions may be (and are) imbued with specific cultural prejudices.  In addition, her previous professional experiences both as a CRM archaeologist and MA student have primed her for two different law careers: one that focuses on indigenous rights & heritage law and one that focuses on immigration & refugee laws within Canada.  

In regards to individuals interested in pursuing an anthropology degree but do not want to take the “traditional academic” route, Lauren provides the following pieces of advice: Anthropology provides a good foundation for any career, in particular because it “unsettles the world around you”.  You recognize that your social world and the institutions that make up society and culture (e.g. politics, gender, education, judiciary, etc.) are all cultural constructs and culturally specific.  There are multiple ways of doing the same thing, which “inspires creative problem solving”.  Individuals who do not take social science courses tend to believe that their cultural context is natural, although it is not, and therefore cannot or do not see how they can change their own social world.  Anthropologists recognize the malleable nature of culture and can, as well as do, make positive changes in the world around them.

*Name changed at the request of the interviewee due to the sensitive and confidential nature of her current work. 

An Archaeologist’s Guide to Dating (the Past): Part 1: Relative Dating

Often times when one thinks about archaeology, one automatically thinks about the cool stuff, known as artifacts, that archaeologists excavate, or uncover, through their field work.  While this is a large part of what is used to interpret the past, these artifacts would be pretty worthless without certain types of information, e.g. provenience, artifact association, location, and in particular a date associated with when the artifact existed and was used.  But how do archaeologists go about dating the past (i.e. the sites and artifacts that they work on)?  If you think it is with flowers and chocolate, you would be mistaken.  Archaeologists actually utilize several different techniques for dating the past, and today’s blog post is dedicated to briefly explaining those methods to you.    

Archaeological dating techniques actually fall within two broad categories: relative and absolute dating.  Relative dating is an archaeological dating technique of identifying objects at a site as either older or younger than an established reference point, whereas absolute dating provides archaeologists a more concrete and precise date associated with the objects found at the site.  Both methods are readily utilized upon excavation of a site as relative dating provides archaeologists with a quick estimate of the age of artifacts (again, relative to an established reference point with a specific date), while the more precise absolute date is collected later after excavations are complete (due to the time and efforts required to obtain that date).  

For further clarification, you can think of the differences between relative and absolute dating as being similar to figuring out an age of a child.  You may see a child and assume a general age category, such as infant, toddler, child, or adolescent.  These would be similar to the relative dating technique described above.  A more specific age, e.g. 5, 8, 11, etc., provides you an exact age of the individual to whom you described by a relative age category, and it is this specific age that is associated with the absolute dates identified above.

Today’s blog post focuses on the two primary types of relative dating: stratigraphy and seriation.  Absolute dating techniques will be discussed in a future blog update.  Stratigraphy is a dating technique that takes into account the soil and rock layers (known as strata) that have been deposited over time in the Earth.  These strata can be deposited through a variety of means, either natural or manmade, and each layer is made up a specific parent material, or source substance, that differentiates one layer from another.  This means that there could be potentially be strata made up of limestone, clay, trash, ash, or other materials.  We are able to determine a relative age of these layers based on the law of superposition, which identifies layers closest to the top soil (the soil that we walk on) as being younger than those deeper in the ground.  You can think of this concept as the Earth’s surface being composed similarly to a layered cake: When one bakes a layered cake, the bottom layer is put down first and therefore would be older than the layer on top that is put down last and is therefore younger (see Figure 1).  Dating objects through stratigraphic analyses takes into account the law of superposition and categorizes artifacts as either younger or older than each other relative to their location within the various strata.

Figure 1: Stratigraphy is like a layered cake.   Photo Credit: Threadless.com

Seriation is different from stratigraphic analyses, although it, too, is a relative dating technique.  Seriation is based on stylistic changes of artifacts over time, whereby the artifacts are identified by their changing styles that occur over a specific time range.  These artifacts make up what is known as a seriation typology, which identifies on a scale the artifacts ranging from oldest to youngest.  An example is shown below (Figure 2).  This typology demonstrates the evolution of Nintendo gaming systems and the gaming graphics associated with each gaming system.   

Figure 2: Seriation Typology of Nintendo Gaming Systems (Google Images)

  

 This typology can be utilized to identify other technological advancements of other gaming systems (e.g. Sega, Play Station, or Microsoft) and/or games associated with this or other gaming systems.  Take for example another famous video gaming system’s archetypal character: Sonic the Hedgehog.  If you were to look at two pictures of Sonic the Hedgehog (see Figures 3 & 4) and compare them to the seriation typology provided in Figure 2, when would you date each Sonic?

Figure 3: Sonic the Hedgehog (Google Images)

Figure 4: Sonic the Hedgehog (Google Images)

Ready for the answer?  Are you sure?  Okay, no more playing hard to get.  The Sonic in Figure 3 was created in 1991, which demonstrates an accurate seriation typology if you guessed that date, but the Sonic in Figure 4 is actually from 2013.  Now obviously you would not have been able to guess that date since there is no 2013 option, the closest you could get would be 2002, but this just demonstrates how this technique is a relative dating technique.  You can not necessarily get an accurate, precise age through utilizing this method.

Seriation as applied to archaeology obviously does not utilize Nintendo gaming systems.  Instead, archaeologists utilize several different classes of artifacts to create their seriation typologies, ranging from pottery and arrowheads to hair styles and burial styles.  The goal of creating a seriation typology is to utilize an artifact class that readily changes over time in both style and manufacture, allowing archaeologists to maximize utility of the seriation typology.

Yearning for more?  If you are satisfied with the first date, stay tuned for the next installment of this two part series where I will be discussing absolute dating techniques.  It may not be a salacious as relative dating, but as this post has hopefully demonstrated, relative dating is not necessarily what it sounds like in popular terms.  It is merely a general means of figuring out an age of a site and/or artifact.  It is the foreplay of archaeological dating.  ;)

(And I promise less dating innuendos in the next post. )

To learn more about archaeology, please visit this trilogy of posts: Part 1, Part 2, and Part 3.

 

Reference:

Feder, Kenneth and Park M. Human Antiquity: An Introduction to Physical Anthropology and Archeology, McGraw-Hill.