Lindsay Blotzer


Department of Earth Sciences

Forensic & National Security Sciences Institute

204 Heroy GL

Email: lbblotze@syr.edu




MS Student FNSSI  and Earth Sciences
Advisor: Scott Samson

Research  Interests

Introduction

Over time, 87Rb decays to 87Sr resulting in varying 87Sr/86Sr ratios across the landscape. This large variation provides great potential as a forensic tool. Typically, older crust has a higher 87Sr/86Sr ratio than younger crust because more time has passed to produce greater amounts of 87Sr. Sr becomes a part of an individual through diet, where it is incorporated into growing tissues recording the same 87Sr/86Sr ratio as the land- there is no fractionation between dietary input and tissues. Therefore, 87Sr/86Sr ratio is useful in studies of migration and provenance. Tooth enamel is linked to where an individual spent their childhood, bone will illustrate the last 10 years of life, while scalp hair shows recent movements. Through this poster, I explore its uses in prehistoric human remains, animal migration patterns, and in the modern human population for forensic purposes (Tipple et al., 2013; Thornton, 2011; Font et al., 2012; Juarez, 2008; Isoscapes, 2010).



Isoscapes: Isotope Mapping

 


Isoscapes Map

Fig. 1. 87Sr/86Sr variation of major bedrock across the contiguous US based on an age model (Bataille & Bowen, 2012).


An isoscape is a map illustrating the variation of an isotope across land. As illustrated in Fig. 1, there is a potential for very different 87Sr/86Sr ratios even in a relatively small area such as upstate New York. Its use has spread into climate research, ecology, trade regulation, animal migration, anthropology, and forensic science driven by improved instrumentation and technology with an emphasis on studying challenges on larger scales (Isoscapes, 2010).



Ancient Human Studies

 

Archaeologists use 87Sr/86Sr to determine the histories of people in differing  burial techniques and possible violent deaths in various ancient cities and civilizations:

* Measuring values in bone and tooth enamel at burial location around the ancient city of Teotihuacan, in Mexico, Price (2000) determined that the large growth in the city’s population was due in part to migration to the city.

 


Teotihuacan stud

Fig. 2. Bar graph of strontium isotope ratios for Teotihuacan study, grouped by location of burials. Paired bone and tooth bars are from the same individual. The local average shows the mean for nine rabbit bones from Teotihuacan (Price, 2000).



 

* At Conchopata in the central Peruvian Andes, Tung and Knudson (2011) examined tooth enamel and bone from burials and trophy heads establishing that the city was mainly populated with local people and their warriors occasionally used militaristic and ritualistic means to take captives from other locales.
* Using tooth enamel, Eerkens et al. (2013) studied an unearthed grave in Central California circa AD 1450 containing 3 individuals. They determined that 2 individuals were born at the site while all 3 lived their teenage years near the site and lived elsewhere as adults. Shortly upon returning, they were killed.


Animal Studies

87Sr/86Sr aids in determining the provenance of illegally acquired animal trophies, ancient animal trade, and animal migration patterns:

* Van der Merwe et al. (1990) studied C, N, and Sr isotopes in bone and ivory of African elephants from different regions of Africa, identifying the area in which the elephant lived, providing a powerful tool for controlling the illegal ivory trade.
* Thornton (2011) reconstructed ancient Maya animal trading by identifying and sourcing non-local animals, determining that deer and peccary were exchanged, having previously been thought to only be of local origin.
* Tree swallow feathers were studied for their O and Sr isotope ratios, representing breeding sites in which the feathers grew, and correctly assigned individuals to their site of origin from less than 40% using only one isotope to 74% with both (Sellick et al., 2009).


Modern Human Studies

These studies of modern humans examines the effects of a non-local diet on 87Sr/86Sr in modern humans, determining if it is a useful tool in forensic science:

* Along with examining hair cleaning techniques, Font et al. (2012), studied movements in 2 modern humans, concluding that modern scalp hair registered Sr isotopic change on a monthly timescale when individuals move to locations with contrasting Sr ratio compositions.
* In 4 forensic cases, 87Sr/86Sr analysis of bone helped aid police in narrowing down the area from where each victim came, leading to positive identification through police inquiry and DNA analysis (Degryse et al., 2012).
* In a pilot study, Juarez (2008) examined modern human hair and teeth of known origin finding 3 distinct regions in Mexico in the dataset, allowing for identification and repatriation of remains of Mexican individuals who died when migrating to the US.

Mexico

Fig. 3. Geographic regions in Mexico with distinct 87Sr/86Sr ratios illustration the potential of Sr isotopes to provenance modern people.

 



Future of 87Sr/86Sr in Forensics

The use of 87Sr/86Sr, like the use of O, C, H, and N isotopes, have been successful in modern forensic science cases, as illustrated in Degryse et al., 2012. However, more accurate isoscapes of strontium need to be created in order for this to be applied over a greater area.  Additionally, the analysis of human hair as a geographic proxy is still in its preliminary stages and its methodology needs to be thoroughly validated. Strontium isotopes are a straightforward and robust technique for identifying residence change and provenance and have great potential in the future of forensic science.

In the coming year, I will analyze and compare body hair in modern humans to determine any fractionation in different tissues. This will be important when examining remains with no scalp hair, forcing a hypothesis that all hair on an indiviual has the same87Sr/86Sr ratio.  Additionally, I will conduct a controlled residence change experiment.


 




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Department of Earth Sciences
204 Heroy GL
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