Quick Tips: Archaeological Techniques – Ground Penetrating Radar.

Ground-penetrating or probing radar (GPR) is a non-destructive, geophysical method that uses radar pulses to image the subsurface. The principles of ground-penetrating radar are similar to reflection seismology, except that electromagnetic energy is used instead of acoustic energy, and reflections appear at boundaries with different dielectric constants instead of acoustic impedances.

Ground-penetrating radar was applied in the 1940’s after the use of radar to detect enemy aircraft’s during WW2. In 1960’s, due to the progression of this surveying technique, it was primarily used to probe and explore the polar ice. By using GPR in relation to these two applications, a P-38 lightening fighter plane was pinpointed within the ice surrounding Greenland in 1992. The P-38 was originally part of a squadron of six fighters and two B17 Flying Fortresses that ditched just over Greenland in 1942. The P-38 fighter plane was later recovered from a depth of 75m.

How does Ground-penetrating radar work? 

GPR works by emitting high frequency, usually polarized, radio waves via antennas, into the ground. If the area being surveyed contains artefacts or hidden archaeology; these electromagnetic waves are reflected back. When the wave hits a buried object or a boundary with different di-electric constants, the receiving antenna records the variations in the reflected return signal. These returned signals are then collected and interpreted to identify any hidden archaeology within the surveyed area.

N.B. Higher frequencies do not penetrate the ground as far as lower frequencies do, but these higher frequencies give a better resolution. Also the radar emitting antennas are usually in contact with the ground for the strongest signal strength; however, GPR air launched antennas can be used above the ground.

Advantages of Ground-penetrating Radar:

  • GPR is non-destructive and not invasive – helping to preserve the archaeology/landscape.
  • GPR can be used in a variety of media/sediments including; rock, soil, ice, fresh water, pavements and structures.
  • It can detect objects, changes in material, and voids/cracks in the ground.

Disadvantages of Ground-penetrating Radar:

  • The depth range of GPR is limited by the electrical conductivity of the ground. As conductivity increases, the penetration depth decreases. This is because the electromagnetic energy is more quickly dissipated into heat, causing a loss in signal strength at depth.
  • In moist and/or clay-laden soils and soils with high electrical conductivity, penetration is sometimes only a few centimetres.
  • Metal can interfere with the electromagnetic radiation – this can give false results.

References:

Balme, J., Paterson, A. 2006. Archaeology in Practice: A Student Guide to Archaeological Analayses. Oxford, UK: Blackwell Publishing. Pg 218.

Renfrew, C., Bahn, P. 1991. Archaeology: Theories, Methods and Practice. London, UK: Thames & Hudson. Pg 249-53.

Click here to read more Quick Tip posts!

Image

Advertisements

Quick Tips: Use of Phytoliths in Archaeology.

Phytoliths are a very important identification tool in identifying plants within ancient environments, often even classifying down to the species of the plant.

But firstly, what are phytoliths? As the name phytolith suggests, coming from the Greek phyto- meaning plants and lith– meaning stone, they are tiny (less than 50µm) siliceous particles which plants produce. These phytoliths are commonly found within sediments, and can last hundreds of years as they are made of inorganic substances that do not decay when the other organic parts of the plant decay. Phytoliths can also be extracted from residue left on many different artefacts such as teeth (within the dental calculus), tools (such as rocks, worked lithics, scrapers, flakes, etc.) and pottery.

Image

Table 1 & 2: Examples of the descriptors found within the International Code for Phytolith Nomenclature (ICPN), 2005, for use of naming phytoliths.
Figure 1: A bulliform phytolith under a microscope, ©Henri-Georges Nation.

Phytoliths can form numerous striking shapes within the plant cells (figure 1), which gives them a characteristic shape, thus aiding the identification of plants. Due to the vast number of shapes and sizes that phytoliths can come in, researchers compiled the International Code for Phytolith Nomenclature (ICPN), 2005. The ICPN was developed to create a standard protocol which is to be used during the process of naming and describing a new or known phytolith type, as well as a glossary of descriptors to help aid with the naming.

To observe phytoliths, a sediment sample needs to be collected preferably away from any human settlements, as the use of agriculture may have introduced non-native plants to the area. The soil sample is then observed under microscope or even scanning electron microscope (SEM). On the discovery of a phytolith after observation it needs to be named using a maximum of three descriptors, the ICPN (2005) can be used to correctly identify what descriptors should be used.

The first descriptor should be of the shape, either using 3D or 2D descriptor (whichever is more indicative/shows the phytoliths symmetry). The orientation of the phytolith should also be noted. The second descriptor should describe the texture and/or ornamentation, if characteristic or diagnostic and not an artefact of weathering.
The third descriptor should be the anatomical origin, but only when this information is clear and beyond doubt (Madella et al, 2005).

Phytoliths are very important and useful if the sediment they are taken from is hostile to the preservation of fossil pollen, so may be the only evidence available for paleoenvironment or vegetation change.

References:

Balme, J., Paterson, A. 2006. Archaeology in Practice: A Student Guide to Archaeological Analayses. Oxford, UK: Blackwell Publishing. Pg 218.

Madella, M., Alexandre, A., Ball, T. 2005. International Code for Phytolith Nomenclature 1.0. Annals of Botany, 96: 253-260. A .pdf of this paper available here.  

Renfrew, C., Bahn, P. 1991. Archaeology: Theories, Methods and Practice. London, UK: Thames & Hudson. Pg 249-53.

Click here to read more Quick Tip posts!

Share Post Sign

Quick Tips: How To Estimate The Chronological Age Of A Human Skeleton – Cranial Suture Closure Method.

This is the 4th blog post in this Quick Tips series on chronologically dating human skeletal remains, if you haven’t read the first post click here to start at the beginning. In my previous blog post I introduced the method of chronologically dating sub-adults using dentition, you can find out this information by clicking here.

Another method of chronologically aging human skeletal remains is by observing the cranial suture closure sites. The human skull has seventeen unique cranial fusion sites (Figure 1), that are positioned on the vault, the lateral-anterior sites, and the maxillary suture. The seventeen sites are:

  1. Midlambdoid                                           10.Superior sphenotemporal
  2. Lambda                                                    11. Incisive suture
  3. Obelion                                                    12. Anterior median palatine
  4. Anterior sagittal                                      13. Posterior median palatine
  5. Bregma                                                    14. Transverse palatine
  6. Midcoronal                                              15. Sagittal (endocranial)
  7. Pterion                                                     16. Left lambdoidal (endocranial)
  8. Sphenofrontal                                         17.Left coronal (endocranial)
  9. Inferior sphenotemporal
Image

Figure 1) Diagram showing the seventeen cranial suture sites.

The first seven fusion sites are on the vault, and the lateral-anterior sites consist of numbers six to ten. Each suture is usually given a numerical score, the score of 0-3 is recommended by the Buikstra and Ubelaker standards (1994). The Buikstra and Ubelaker (1994) scoring system is as follows;

  • 0 is given when the suture is open, meaning there is no evidence of ectocranial closure.
  • 1 is given where there is a minimal closure of the suture.
  • 2 is given to sutures with evidence of significant closure.
  • 3 is given to a completely obliterated suture (complete fusion).

So to attain the age of a skeletal remain you would total the scores for each grouping of sites, vault (1-7) or lateral anterior (6-10), and by comparing the scores to the known composite scores vs. chronological age of Meindl And Lovejoy, 1985 (Figure 2).

Image

Figure 2: Table demonstrating Meindl and Lovejoy (1985)’s composite scores of the sutures on the vault and lateral-anterior, respectively, in relation to mean chronological age.

A very useful cranial suture site is the sphenooccipital synchrondrosis, because at least 95% of all individuals have fusion here between the ages of twenty and twenty-five, with most individuals experiencing complete fusion around the age of twenty-three (Krogman and Işcan, 1986).

References:

Buikstra, J.E., Ubelaker, D.H. 1994. Standards for Data Collection From Human Skeletal Remains.Fayetteville, Arkansas: Arkansas Archaeological Survey Report Number 44.

Krogman, W.M., Işcan, M.Y. 1986. The Human Skeleton in Forensic Medicine (2nd Ed). Springfield, Illinois: C.C. Thomas.

Meindl, R.S., Lovejoy, C.O. 1985. Ectocranial Suture Closure: A Revised Method For The Determination Of Skeletal Age At Death Based On The Lateral-Anterior Sutures. American Journal of Physical Anthropology. 68, 57-66.

White, T.D., Folkens, P.A. 2005. The Human Bone Manual. San Diego, CA: Academic Press. Pg 360-385.

This is the forth of a Quick Tips series on ageing skeletal remains, the next in this series will focus on the use of the pubic symphyseal surface to chronologically age skeletal remains. To read more Quick Tips in the meantime, click here

To learn about basic fracture types and their characteristics/origins in their own Quick Tips series, click here!

Share Post Sign

Quick Tips: How To Estimate The Chronological Age Of A Human Skeleton – Using Dentition To Age Subadults.

This Quick Tips post is the third in the series on age estimation of human skeletal remains, if you haven’t read the first post click here to start at the beginning. The first post provides an overview of the different techniques utilised by archaeologists/anthropologists, which will each be covered in more detail in their own blog post, and the categories that human skeletal remains are placed under according to their chronological age. The second post examines the epiphyseal closure method, which you can find here.

The practice of using dentition to chronologically age human skeletal remains is split into two halves, depending on the whether the skeleton is that of a subadult or adult. This blog post is going to discuss using dentition to age subadults.

Due to the abundance of teeth found in many archaeological, forensic, paleontological, and anthropological contexts and because of the regular tooth formation and eruption times, dental development is the most widely used technique for aging subadult remains. As stated in my previous blog post, several elements of the human skeleton begin the stages of epiphyseal fusion alongside the conclusion of tooth eruption; these two techniques (dentition and epiphyseal closure) are often used complementary to each other to help age sub-adults. When it comes to subadult tooth emergence there are four stages:

Stage 1 is where most of the deciduous teeth, commonly referred to as ‘milk teeth’, emerge during the second year of life.

Stage 2, during this stage the two permanent incisors and the first permanent molar emerge, this stage typically occurs between the age of six and eight years.

Stage 3, occurs between the age of ten and twelve and it involves the emergence of the permanent canines, premolars, and second molars.

Stage 4, or the final stage involves the third molar emerging around the age of eighteen years.

When looking at dentition you must look at all aspects of emergence and not just at the fully erupted tooth, which includes the completeness of all roots and crowns (formation) and the position of each tooth relative to the alveolar margin (eruption). Ubelaker (1989) conducted a study on non-Native Americans and created a graphic summary of dental development and the correlating ages it occurs, see figure 1.

Figure 1: Ubelaker's (1989) diagram showing the dental development in correlation to age.

Figure 1: Ubelaker’s (1989) diagram showing the dental development in correlation to age.

It must be noted that the ages these stages occur at differ per individual so only act as a reference. Gustafson and Koch (1974) created a graph to illustrate the variation that could occur with dental development, see figure 2.

Figure 2: Gustafson and Koch's (1974) image showing the variation in timing of dental development. Colour key: Black highlights the age that crown mineralization begins, Dark grey shows the age of crown completion, Light grey shows the age of eruption, and White displays age of root completion.

Figure 2: Gustafson and Koch’s (1974) image showing the variation in timing of dental development. Colour key: Black highlights the age that crown mineralization begins, Dark grey shows the age of crown completion, Light grey shows the age of eruption, and White displays age of root completion.

References:

Gustafson, G. Koch, G. 1974. Age estimation up to 16 years of age based on dental development. Odontologisk Revy. 25. Pg 297-306.

Ubelaker, D.H. 1989. Human Skeletal Remains: Excavation, Analysis, Interpretation (2nd Ed.). Washington, DC: Taraxacum.

White, T.D., Folkens, P.A. 2005. The Human Bone Manual. San Diego, CA: Academic Press. Pg 360-385.

This is the third of a Quick Tips series on ageing skeletal remains, the next in this series will focus on the use of dentition to age adults and the use of cranial suture closure. To read more Quick Tips in the meantime, click here

To learn about basic fracture types and their characteristics/origins in their own Quick Tips series, click here!

 

Quick Tips: Named Fractures – Part One: Hand & Forearms

This blog post is the 3rd in its series on bone fractures. To view the first blog post on the basic fracture types and information, including open and closed fractures, click here.

This blog post will highlight some of the common ‘named’ fractures you will often find in archaeological and anthropological settings. It is important to know their characteristics and common causes to help establish what happened – whether the fracture was received by defensive or offensive action, or purely accidental. This blog post will examine the first five common fractures associated with the hand and forearm bones.

Image

Common ‘Named’ Fractures of the forearms and hands: A) Boxer’s fracture, B) Bennett’s fractures, C) Parry’s or Monteggia’s fracture, D) Colles’ fractures, and E) Smith’s fractures.

The first two fractures we will look at affect the metacarpal bones;

A)     Boxer’s fracture: This fracture occurs due to the axial loading, meaning a force was applied along/parallel to the axis of the bone, on the transverse neck of the 4th and 5th metacarpal, secondary to an indirect force. A Boxer’s fracture often happens due to punching an object/person with a closed fist, hence the name ‘Boxer’ being associated to it.

B)      Bennett’s fracture: This fracture affects the 1st metacarpal (thumb) and extends into the carpometacarpal (CMC) joint which is complicated by subluxation (dislocation of a joint). A Bennett’s fracture is an oblique (See 1st blog post for meaning, click here) intra-articular metacarpal fracture caused by an axial force directed against the partially flexed metacarpal. This injury is also common when someone punches a hard object, but its most common cause is falling onto the thumb. An example of this is falling off a bike, as the thumb is extended around the handle bars.

The last three fractures affect the longbones of the forearm, the ulna and radius;

C)      Parry’s/Monteggia’s fracture: This fracture occurs on the proximal third of the ulna with subluxation of the radius/ulna. The most common cause of this fracture is by blunt force trauma caused by lifting the forearm up to protect the head or body in defence from an oncoming attack/striking object.

These two fractures affect the distal radius but cause displacement in two directions;

D)     Colles’ fracture: A Colles’ fracture, also known as a “dinner fork” or “bayonet” fracture, occurs when the distal radius is broken with dorsal displacement of the wrist and hand. This fracture is common when the person falls forwards and uses their outstretched hand to cushion the fall, which causes the force to displace and break the head of the radius.

E)      Smith’s fracture: A Smith’s fracture is the same as the Colles’ fracture but with ventral displacement of the broken radius head. The cause of a Smith’s fracture is the same as the Colles’ fracture, but it is less common.

Image

Fractures: D) Colles’ fracture, and E) Smith’s fracture.

The next Quick Tips post will discuss other ‘named fractures’ in archaeological/anthropological situations and their causes and characteristics.

This is the third post of a set on fractures, so keep your eyes open for the other posts, and the new ones to come. To view all the other Quick Tips posts click here!

Share Post Sign

Quick Tips: Forensic Entomology – An Introduction.

What is forensic entomology? It is a discipline within forensic sciences where specialists use information that they know about insect lifecycles and behaviours to interpret evidence in a legal context, relating to humans and animals. Entomologists don’t just stick to insects; their work can expand to include other arthropods, mites, spiders and macro-invertebrates.

Image

Insect species which are relevant to forensic entomology

What information can we learn from insect activity? Insects are everywhere and can hardly be avoided, so it’s no surprise that sometimes they get mixed up in the evidence left behind – making them extremely valuable to an investigation. Insects can be a vital part of forensic science as they can provide a time and date to a crime or even a geographical position to where it happened. As some insects only become apparent during certain months, they can become a biological calendar for when a crime might have been committed. As well as being a biological calendar, certain insect species are only native in specific countries or hemispheres. This can be used to create an ‘X marks the spot’ on where a crime was committed – even if a body was moved/buried. Because of this, insects can be the key to past and present events as well as the future.

The insects that are particularly relevant to forensic entomological investigations are blow flies (diptera), flesh flies, cheese skippers, hide and skin beetles, rove beetles and clown beetles. These forensically relevant insects can be placed in four categories:

  • Necrophages, which feed only on the decomposing tissue of the body or body parts. This is the category that blow flies, hide beetles and clown beetles are classed under.
  • Predators of the necrophages – for example the rove beetles and ground beetles.
  • Omnivores that consume both the live insects inhabiting the corpse and the dead flesh – ants and wasps.
  • Opportunist species, which arrive because the corpse is a part of their local environment. This is where mites, hoverflies, butterflies and occasionally spiders are classified.

Forensic entomologists use the evidence they gain from studying insects within legal cases in either civil or criminal courts. Civil court cases include:

  • Insect infestation in urban contexts.
  • Stored product infestations/pests.

Criminal court cases include:

  • Neglect – either animal or human (elderly and children).
  • Insect infestation of a body – living or dead.
  • Death in which foul play is suspected.

This is just an introduction into the world of forensic entomology, if you’d like to know more or further your knowledge on this topic check out this book, I found it very interesting and a terrific read:

  • Forensic Entomology: An Introduction (UK/Europe)
    Forensic Entomology: An Introduction (US/Worldwide Link)
    by Dorothy Gennard. Rating – ***
    “I used my this for my blog post on the basics of forensic entomology. It is perfect if you’re unsure on whether or not you want to pursue this career/discipline. Definitely a good read if your interest is sparked by Dr Hodgins from ‘Bones’, as it explained everything involved within entomology under legal settings.”

Quick Tips: How To Estimate The Chronological Age Of A Human Skeleton – Epiphyseal Closure Method.

This Quick Tips post is the second in the series on age estimation on skeletal remains, if you haven’t read the previous post click here. The previous post provides an overview of the different techniques utilised by archaeologists/anthropologists, which will each be covered in more detail in their own blog post, and the categories that human skeletal remains are placed under according to their chronological age.

One of the methods frequently used by archaeologists/anthropologists to estimate the chronological age of human remains is by studying the level of epiphyseal fusions.

But first what is an epiphysis? An epiphysis is the cap at the end of a long bone that develops from a secondary ossification center. Over the course of adolescence the epiphysis, which is originally separate, will fuse to the diaphysis. The ages of which epiphyseal fusion begins and ends are very well documented, with the majority of epiphyseal activity taking place between the ages of fifteen and twenty-three.

Epiphyses

Diagram showing where the epiphysis is found.

As epiphyseal fusions are progressive they are often scored as either being unfused (non-union), united, and fully fused (complete union). Females often experience the union of many osteological elements before males, and every individual experience epiphyseal union at different ages.

Left: Diagram of a skeleton showing the position of the different epiphyseal elements. Right: A graph displaying the timing of fusion of epiphyses for various for various human osteological elements. The grey horizontal bars depict the period of time, in ages, when the fusion is occurring. All of the data is representative of males, except where it is noted. Data taken from Buikstra & Ubelaker, 1994.

Left: Diagram of a skeleton showing the position of the different epiphyseal elements.
Right: A graph displaying the timing of fusion of epiphyses for various for various human osteological elements. The grey horizontal bars depict the period of time, in ages, when the fusion is occurring. All of the data is representative of males, except where it is noted. Data taken from Buikstra & Ubelaker, 1994.

Archaeologists/anthropologists use standards that are well known and documented, such as Buikstra & Ubelaker’s (1994) depicted in the above graph. From the above data we know that, for example, the fusion of the femur head to the lesser trochanter is begins around the age of fifteen and a half and ends around the age of twenty. So if a skeleton has evidence of an unfused femur head/lesser trochanter, there is a possibility of the skeleton having a chronological age of < fifteen years. If there is full union of the epiphyses then the skeleton is more than likely being > twenty years old. But it should be noted that individuals vary in their development so numerous elements should be examined before coming to an accurate conclusion.

Different stages of epiphysis fusion of human tibias. Ages left to right: Newborn, 1.6 years old, six years old, ten years old, twelve years old and eighteen years old.

Different stages of epiphysis fusion of human tibias. Ages left to right: Newborn, 1.6 years old, six years old, ten years old, twelve years old and eighteen years old.

As several elements of the human skeleton begin the stages of epiphyseal fusion alongside the conclusion of tooth eruption, these two techniques (dentition and epiphyseal closure) are often used complementary to each other to help age sub-adults. The next post in this series on age estimation will focus on the use of dentition to aid with the chronological ageing of human remains.

References:

Buikstra, J.E., Ubelaker, D.H. 1994. Standards for Data Collection From Human Skeletal Remains. Fayetteville, Arkansas: Arkansas Archaeological Survey Report Number 44.

White, T.D., Folkens, P.A. 2005. The Human Bone Manual. San Diego, CA: Academic Press. Pg 360-385.

This is the second of a Quick Tips series on ageing skeletal remains, the next in this series will focus on the dentition method of ageing sub-adults. To read more Quick Tips in the mean time, click here

To learn about basic fracture types and their characteristics/origins click here!