Last week I discussed a way of preserving bodies almost indefinitely in some cases: embalming. On the other side of this is decay, the process of bodily decline and biological breakdown of the flesh. If you’ve ever watched any of the forensics crime shows, you know that understanding decay and changes in the body can be a key factor in determining when the individual died and how the body was treated after death. But its also important for archaeologists dealing with remains that are ancient.
First, let’s look at the early stages of decay. I won’t go into the gooey details, but following death the flesh of the body goes through five stages. The first stage consists of the ‘mortis‘ phases. The blood isn’t being pumped through the body so due to gravity it pools in certain areas, and this is known as livor mortis. Shortly after this, the muscular tissue becomes rigid and incapable of relaxing, a state called rigor mortis. Next the body loses heat and cools in a process called algor mortis. Second, the body goes through bloat, in which means that microbes are rapidly growing and forming gases within the body. This is also usually when bugs and insects begin to feed and reproduce on the remains. In the third stage there is rapid loss of mass due to insect feeding and natural purging of fluids due to decomposition. Advanced decay is the fourth stage, and there is little left of the body at this point. Finally, the last stage is skeletonization when no flesh remains. But this isn’t the end- bones are also subject to continued decay, the study of which is known as taphonomy and is extremely important for archaeologists.
Taphonomy is the study of what happens to remains after the death of the living creature. Usually, the focus of these studies for archaeologists is to determine why there is a bias in the archaeological record (i.e. why certain bones preserve in certain conditions and others do not). Human remains do not always appear as clean bones in the ground. Sometimes they are badly degraded, not all bones may have survived through time, and in certain conditions the skeleton is no longer present. Taphonomic studies try to determine why certain bones are present, and others are not. Here are two examples. The left hand side is an Anglo-Saxon burial where the bones are fairly well preserved. Obviously we are missing some ribs and the ends of the long bones did not preserve well, however it is intact enough that we can gain insight into who this person was based on the remains. The right hand side shows the complete opposite where no bones at all were preserved in the burial. This means we cannot learn anything about the person biologically, and must rely on the grave goods alone. Both are from the same country and same time period- so why such a difference in preservation? This is what taphonomic studies hope to answer.
There can be extrinsic (external) factors, or intrinsic (internal) factors that effect preservation. Soil characteristics have a major effect on whether bone is preserved. As soil temperature and acidity increases in the soil, it is less likely that the bone will be preserved. Types of soil also affect whether bone is preserved: sand can preserve bone very well, whereas salt and chalk are destructive to bone (for more on these external factors see this article by Baxter). Other factors include water, which in an anaerobic environment causes preservation and aerobic causes destruction. Internal factors like the porosity of the bone can also affect preservation. The bones of the very old or very young are often more porous due to osteoporosis or lack of development, respectively. In cemeteries we rarely find infant remains, which could be due to the fact that they don’t preserve well or that they are buried elsewhere (see this post on an infant burial site for more information on this occurrence).
Cultural practices can also affect how well bone is preserved. For example, if the body is buried in a bog it may be perfectly preserved, whereas if it is buried in acidic soils it could be completely destroyed. Burial disturbances such as exhumation, additional interments, and other intrusive actions can lead to bone being more susceptible to decay. A study done by Lieverse et al. (2006) found that “primary burials exhibited higher completeness and increased articulation compared to secondary burials”, and those that were primary burials were better preserved. Factors such as burial location, depth of burial and container also were important in determining how well the bones preserved. They concluded that cultural practices were a prime agent of bone destruction or preservation. Those bones which were disturbed by human agency were less well preserved than those which weren’t disturbed by cultural action.
Taphonomy drastically effects what we find and how much we can analyze. It is important to know why bones aren’t as well preserved as others, and what factors may have erased them completely. While this isn’t an exhaustive list of what can affect bones, it is a good beginning!
Lieverse, A., Weber, A., & Goriunova, O. (2006). Human taphonomy at Khuzhir-Nuge XIV, Siberia: a new method for documenting skeletal condition Journal of Archaeological Science, 33 (8), 1141-1151 DOI: 10.1016/j.jas.2005.12.001
I’ve seen first hand the examples of how differently bones can be preserved in dissimilar soils when I was occasionally involved with the (authorized and legal) exhumation of human remains. In this specific case, the two bodies had been buried 20 – 25 years ago in the same cemetery about 150 m. apart, but the one buried where the pine trees grew (acidic soil) were in very poor condition, and many of the smaller bones were not to be found, and the ones in the grassy part of the cemetery which had sandy soil were in remarkably good condition. Both skeletons were of adults (one male the other female), and of similar size and age at the time of death. Also interesting to note is how well the synthetic cloth stood up to the test of time even in the acidic soil.
Thanks for the great example! It’s interesting how much preservation can vary due to simple environmental differences.
This is such an interesting post! I am not expert in anything like this, and try hard to understand it from an interest perspective, and you have a great ability to write really clearly and precisely! Fab!
oh hey, this was the title to my honour’s thesis way back in 2009
Cool! Did you look at bones or flesh?
I looked at bones from a potential massacre site in South Africa
The Mississippian period stone box burials in numerous sites along the middle Cumberland River in the vicinity of Nashville, Tennessee, tend to have excellent bone preservation. The Middle Cumberland region is dominated by Ordovician period limestones that occur in relatively flat, thin beds. Therefore, the eroded limestone often presents itself (in creeks beds) as large, thin, easily shaped slabs.
The Mississippian occupants of the area would excavate elongate, rectangular pits in the soil that were large enough to accomodate a human body that needed to be buried, line the floor of the pit with limestone slabs (sometimes broken pottery), line all four sides of the pit with limestone slabs, place the body in the box (along with burial furniture), and then cap the box with limestone slabs. Over hundreds of years, soil would gradually enter the stone boxes through cracks between the limestone slabs and fill the boxes all the way to the top with soil. In addition, soil would often cover over the entire box, sometimes in depths up to 2 feet. However, the calcium carbonate (a base) in the limestone encasing the body would effectively titrate the acid in the soil and slow down natural destruction of the interred person’s bones. As a result, the Mississippian skeletal collections from the Nashville area tend to be fairly well preserved.
Similar preservation for Middle and Late Archaic period burials occurs in the same area when those burials are interred (without stone boxes) in soils that contain high volumes of aquatic snails.
Early Archaic and Woodland Period remains in Middle Tennessee, which were most often buried in soil with no surrounding limestone slabs or shell, tend to be very poorly preserved, particularly in the Eastern Highland Rim area where soils are very acidic, All that remains of many burials in such areas are remnant pieces of sturdy long bones such as the femur and tibia, a few cranial fragments, and teeth. Truthfully, teeth are about the most survivable portion of an interred human body in such areas of acidic soil.
Very interesting- had not heard about that before. Thanks for all the great examples of differential preservation!
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Nice article. I worked in a mortuary for 7 years. Its a very fascinating job, working with forensics at crime scenes. However, forensics is a difficult industry to get into here in South Africa.
I know what you mean, currently trying to find a way to get in with my bioarchaeology skills.
Congratulations Kathy, this is a very synthetic post and it will be definetely be useful for people that doesn’t know about the subject. I’m a physical anthropologist and I find this very refreshing and helpful, I will definitely recomend your blog to people interested on the subject.
Keep up the great work 🙂
Thank you so much! Glad it was helpful!
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Hello Kathy, I have come across your site by chance, whilst I have been Googling for information on whether the bones of my baby brother would still be available in his grave 60 years from his burial. He was 11 months when he died, and was buried in a small infant coffin. Given what one of your respondents has said about the actual location of a grave in a cemetery, and how that contributes to the degree of deterioration – his grave is in a grassy area (quite dry at present) with no trees in the immediate surrounds.
Whilst this is an enquiry at this stage – and may yet prove to be preposterous (and hugely costly) – I have been considering having his remains (should they be there) moved to the crematorium, alongside my (and his) parents.
Your advice/opinion would be greatly valued.
Barbara- chances are there is still some preservation of ligament or hair if the remains were preserved in anyway (which they usually are), but for the most part decomposition occurs between 10 and 12 years in funeral-preserved remains. However, you could cremate them regardless if your intent is to place him in a crematorium. I’m not sure about regulations or cost. Honestly, I tend to deal more with historic deceased so I’m unsure of the actual feasibility of this. However, I think it is a wonderful gesture and wish you luck!
the mummification process is a prime example of the ancient Egyptians attempting to prevent the decay of their remains. for the hope of resurrection in the future. the treating of cloth with certain chemicals and then wrapping the remains of the dead tightly for the preservation of the wealthy, was common practice.
How long would it take an human skeleton to disintegrate if it was exposed to oxygen? That is it was not buried or embalmed.
First off, the bones wouldn’t disintegrate if left in the open air. They would likely be eaten or gnawed by animals, birds, and bugs. Open air burials will quickly vanish if the right animals are around. Tibetan sky burials take very little time for a body to disappear (though the bones need to be broken down in order for the birds to eat them quickly). If the bones weren’t disturbed at all (say in a museum collection) they can last for centuries before becoming too fragile, and if within the perfect dry conditions you can find bones that are in fabulous condition. So I guess the real answer is that it all depends on the context.
Thank you Kate. I ask out of curiosity – a woman’s body was found in her apartment and the only thing left was her dentures. If the apartment was closed completely and the only animals or bugs would be the usual insects found in an apartment how long do you think it would take for her bones to disintegrate?
poorly stated previous post – a woman was discovered to have died no bones remained
Very interesting information, and it explains a few things. There is a small graveyard not far from where I live. The most recent burial was in the 1960s and the first burials were in the late 1800s. There are many infant graves in the cemetery, with tombstones giving only a date of death, no date of birth. I often visit the cemetery to think about the lives of the people interred there, especially the ones that lived and died back in the pioneer days.
Recently prairie dogs have been digging into the cemetery. Not much can be done about it since prairie dogs are considered as an endangered species.
Last week while visiting the cemetery, I saw bones laying on the ground outside of one of their tunnels. When I got home I looked up diagrams of the human skeleton and realized many of the bones I saw were likely the bones of infants buried in the cemetery. Some of the bones look to be that of a baby’s skull, though the skull is not intact. What I was seeing were parts of a jaw and the orbit of an eye.
I was mortified at the thought that such a young child had had their skull shattered before they died. Now that I know that bones can decay quickly in some cases, I can take some comfort in the thought that these skull bones may have fallen apart naturally, and the child did not suffer a severely traumatic death.
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Yes this very true after death!!
Thank you for a succinct explanation. This information is something I need for a fictional story I am writing. Cheers!
I love hearing this research is being used for fiction! Feel free to share it when you’re done!
Just used this for a 6th grade discussion in archaeology. Thanks for the good write up.
Thanks! I’m glad to hear this was useful!
How long does it take for bones to decompose? I am trying to explain to a friend why there are not bones everywhere from all the dead species that have ever lived. but I can’t seem to find an average lifespan of bone in general before it disappears (Decomposes). I understand that the conditions need to be right for a bone to fossilize but am i right in thinking that the reason there are not bones everywhere is because most of them decompose completely? And how long does it take? (on average)?
This is a super tricky question due to the high variation of preservation of bone based on treatment, soil and context. First off, the reason you don’t see animal bones everywhere is primarily because other animals will eat or gnaw on the bones. Rodents have teeth that are constantly growing, so they chew on material like bone to reduce this growth and keep teeth sharp. Around me (Northeast US) this is how many bones vanish. Lots of animals will gnaw away at remains. Soil can also cause bone to decay quickly if it is highly acidic, like a decade or so. But if the conditions are dry or cold or non-acidic it can take hundreds and hundreds of years.
Is it fair to say that bones more than 100 thousand years old that are in any type of soil or earth will have decomposed completely unless they are in specific conditions like ice or rock?
At that age they would either be decomposed or fossilized. Any bones we find at that age are fossils.
So the answer is NO?
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Katy, please would you give me an opinion? This is a serious question, I am not joking. My mother’s property is about to be sold and I am wondering if the bones of my 6-pound Maltese dog, that I buried there in a cardboard box, wrapped in a baby blanket, in 1976, would still exist? It has bothered me for years that my wonderful stepfather unknowingly removed the marker to Sammy’s grave. I have played ostrich for so many years but now all of a sudden I will lose access to her yard, and am wondering if there would be a point to trying to hunt for the bones. Honestly this is a real question. He was my baby.
Hi Janet, this is a tough thing to answer. I would need to know a lot about the soil, moisture, rainfall, weather fluctuations, type of box, etc. in order to help you determine this. Sorry I can’t be of help- without loads of environmental information I can’t comfortably say yes or no.
What an interesting conversation…..only other area that might need some discussion for this audience is why dinosaur bones, hundreds of millions of years old can exist. Quick answer…..they are not made of bone!! So what goes on here? All my best to you Ms. Emery….signed …ole rock picker at USGS.
Fossilized bone is more rock and minerals than bone itself. It takes just the right conditions for fossilization to occur, which is why certain areas of the world (like the Badlands in the United States) have a ton of fossils while other areas have little to no fossils at all. When volcanoes such as Yellowstone erupt, the sheer amount of ash that can be dumped over a large region can lead to fossilization of remains trapped deep beneath the ash fall.
Can you tell me, If a person, who lives alone in a reomote place [Say some where in London], is dead in his home [Like a Heart Attack]. And if no one sees him for a couple of years, what will be condition of that dead body that’s been there in the open, like in the ambient temprature. I mean, surely there will be no flesh, but exactly how much time does it take for the disappearance of the bones & skeleton? I just wanted to know the time frame, Katy.
I’ve surfed many articles before, but after seeing your article I finally understood that you’re the expert I need to ask my doubt 🙂
And by the way, Loved your article and It’s got like tons of info, I never came across.
Thank you Katy 🙂
I am Science teacher at Allied school whilts I was searching about decomposition I came across your page which have much information about bones preservation… and I was shocked to know that in dead body preservation certain soil differences played important roles….. soo that page increased much of my knowledge…..m.
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Are there simple fill-ins for the blanks below?
Without embalming, the flesh of a dead body usually lasts about _______ years.
Without embalming, the bones of a dead body usually last about __________ years.
Nope- it is complex and based on weather conditions, soil conditions, what condition that body was in, etc. No hard and fast rules for this!
Hi, I would like to ask a question related to my research prior to writing a novel and wonder if this thread is still live. Many thanks, Kathryn
It is best to email me at firstname.lastname@example.org with questions!