{"id":35660,"date":"2016-07-21T12:19:01","date_gmt":"2016-07-21T16:19:01","guid":{"rendered":"http:\/\/www.bumc.bu.edu\/busm\/?p=35660"},"modified":"2016-07-21T12:19:01","modified_gmt":"2016-07-21T16:19:01","slug":"bone-detective","status":"publish","type":"post","link":"https:\/\/www.bumc.bu.edu\/camed\/2016\/07\/21\/bone-detective\/","title":{"rendered":"Bone Detective"},"content":{"rendered":"

Understanding bone weathering may help determine time of death<\/h4>\n
\"Forensic
Forensic anthropologist James Pokines studies how bones \u201cweather,\u201d or break down when left outside. His recent work found that freeze-thaw cycles are an important component of weathering.<\/figcaption><\/figure>\n

About once a month, James Pokines<\/a> has a case at the state Office of the Chief Medical Examiner<\/a> that requires extra attention. Pokines, assistant professor of anatomy and neurobiology<\/a>, is also the forensic anthropologist for the Commonwealth of Massachusetts. \u201cAny bones that come to the morgue,\u201d he says, \u201cgo to me.\u201d<\/p>\n

People find bones all the time: washed up on the beach, caught in a scallop rake, dispersed out in the woods, dug up during home renovations, and even\u2014seriously\u2014hidden away in grandma\u2019s closet. Most bones sent to the morgue are humdrum, easily identified as deer, chicken, or even melted plastic. But it\u2019s those once-a-month cases, when somebody sends in, say, a femur that is actually bone, and actually human\u2014that pique Pokines\u2019 interest. His job is to determine, as best he can, the sex of the person, their ancestry, stature, and age at death. He also studies the field of science known as taphonomy: the changes that living organisms undergo from the time of death until their remains are preserved (or not) as a fossil. But crime investigators want more: they want to know how long it has been since a person died. This information is often beyond the grasp of forensic science, though Pokines and his colleagues are working to change that, most recently with research published in the March 17, 2016, Journal of Archaeological Science: Reports<\/em><\/a>.<\/p>\n

\u201cThe condition of the bone depends entirely on where you put it\u2014every microclimate is a little different,\u201d says Donald Siwek<\/a>, a research assistant professor in the Department of Anatomy & Neurobiology at the School of Medicine. \u201cSo you can\u2019t just look at a bone and say it\u2019s two years old. If you\u2019re good, you can say it\u2019s recent, but if you want to get closer than that, it\u2019s hard to do. That\u2019s why it\u2019s a big area of research.\u201d<\/p>\n

A bone left lying outside will eventually disintegrate in a process called \u201cweathering,\u201d which is one component of taphonomy. Forensic scientists use a six-stage weathering scale, with \u201c0\u201d meaning not weathered at all, and \u201c5\u201d meaning that the bone is crumbling into dust and splinters. But how quickly a bone goes from 0 to 5 depends on many factors: UV light from the sun, minerals from groundwater, heat, humidity, wetting and drying, and freezing and thawing. Research on each of these factors is scarce, but Pokines recently shed light on one: the freeze-thaw cycle.<\/p>\n

Scientists can routinely estimate the age of ancient bones\u2014like those from mummies\u2014though carbon dating. They can also determine the age of younger bones\u2014like those from a recent murder victim\u2014by studying the state of decomposition of the body, and the types of insects swarming the scene. But it\u2019s those in-between bones, the ones that have been lying in the woods for a year, or a decade, that puzzle forensic anthropologists like Pokines.<\/p>\n

\"Deer
Deer bones. Scientists froze and thawed the bones 75 times, then measured cracks on the surface and inside the bone.<\/figcaption><\/figure>\n

\u201cIf a body has been lying outdoors for a year, two years, three years, how do I know how long it\u2019s been out there? That\u2019s the hard thing, that middle gap,\u201d says Pokines. \u201cThat\u2019s one of the things that we\u2019re researching: Can we tell how long the body has been there, when everything else is washed away, when the clothing is decomposed, when any ID they had is either gone or was never there.\u201d<\/p>\n

To examine how repeated freezing and thawing affects bones, Pokines and his researchers\u2014mostly students\u2014started with the dried leg bones of 93 deer. (Why deer? They\u2019re free, plentiful, and roughly human size, says Pokines.) They covered large plastic trays with moistened pads, spread the bones on top, and sealed the trays in giant plastic bags. Then they froze the bones. And thawed them. And froze them. And thawed them. They repeated the freeze-thaw cycle 75 times, stopping every 25 cycles to examine how the bones were changing.<\/p>\n

While Pokines expected the repeated freezing and thawing to crack the bones\u2014after all, that\u2019s what happens to rocks\u2014he wasn\u2019t sure exactly how or where the bones would break. What his research group found: on the bone\u2019s surface, long cracks all along the shaft. Then, he and his students cut the bone into thin, circular slices and examined them under a microscope. They found tiny micro-cracks within the structure of the bone, as well: \u201cIt definitely seems like a component of what\u2019s going on with the bones starting to fall apart,\u201d he says. The next step is to quantify these results, so that that they may eventually help investigators determine the age of a bone, and how long it\u2019s been exposed to the elements.<\/p>\n

\u201cOn TV they say, \u2018this person\u2019s been dead exactly 72 hours\u2019\u2014that\u2019s not how it works,\u201d says Siwek. \u201cWe want to be able to give law enforcement an \u2018accurate estimate\u2019 of the time of death. That\u2019s the job of the forensic anthropologist. But so many environmental factors come into play; that\u2019s why it\u2019s hard, but also why it\u2019s important.\u201d<\/p>\n

Ultimately, says Pokines, the freeze-thaw cycle is just one piece of the forensic puzzle. He suspects that repeated wetting and drying of bones may play an even larger role in weather than freezing and thawing alone. \u201cWe hope other scientists will perform similar research into what makes bones weather,\u201d says Pokines. \u201cWe\u2019re trying to separate all these different factors, and the freezing and thawing is just one part of what\u2019s going on.\u201d<\/p>\n

This BU Today story was written by Barbara Moran<\/a>. Photos by Jackie Ricciardi<\/span>
\nA version of this story was originally published in <\/em>BU Research<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"

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