Dem bones
Question: Fluffy, my pet guinea pig, died recently. We buried him in a
cardboard shoebox about 75 centimetres down. I am driving my mom mad by asking
if Fluffy is just bones yet. Is he? And if he isn鈥檛 when will he become just
bones? And if he doesn鈥檛, what will happen to him?
鈥擠imitri Maxwell
Fluffy was buried four weeks ago in the San Francisco Bay area, which has a
temperate climate. I am constantly being asked by Dimitri, 鈥淚s Fluffy bones
now?鈥� I would appreciate some detailed information on decomposition and the time
involved in order to help me answer the question. The topic may sound a bit
gruesome for an 8-year-old but my son thrives on science.
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鈥拟辞尘
Answer: Dear Dimitri鈥檚 Mom,
Thank you for sending Dimitri鈥檚 very interesting question to New
Scientist. My husband and I are field biologists who teach at a college,
run a consultancy and also have a farm not far from the San Francisco Bay area.
Dimitri鈥檚 enquiry didn鈥檛 seem in the least strange or macabre to me. Teaching
has shown me that elementary schoolboys have a great interest in all aspects of
the decomposition side of the food chain.
Dear Dimitri,
It鈥檚 a very hard one to answer precisely. My husband and I are biologists and
long-time farmers in your area. Farmers, especially those who raise livestock,
bury a lot of small animals over the years. We have also prepared many animal
carcasses or parts of them as study specimens. And yet we still don鈥檛 always
know what to expect when an animal starts to decompose.
There are a great many variables, different factors which change the time it
takes for all the flesh and skin and fur to leave the bones. My guess is that
Fluffy won鈥檛 be 鈥渏ust bones鈥� for at least six more months, and because he was
buried pretty deeply and in a box, I鈥檇 expect the whole process to take a year
or more.
This is based on what happens to gophers and rats, animals about the size of
Fluffy, when we bury them here鈥攁nd we鈥檝e buried many over the years. The
body will be worked on by a huge number of organisms whose job it is to return
plant and animal tissue to the soil. They are of all kinds and all sizes and, as
a group, are known as decomposers. I outline some of their details and
characteristics below.
Bacteria and fungi that live in the soil and within the body itself will work
on the soft parts of the animal, eventually returning the elements to the earth
to nourish plants and soil organisms. There are three obvious variables in this
part of the cycle.
The first is that some soils have a lot more bacteria than others.
Secondly, most of these microorganisms need oxygen. The deeper you go into
the ground, the less oxygen there is in the soil, and I see that Fluffy is
buried pretty deep.
Finally, most of the decomposer microorganisms like it warm and moist. Your
soil is probably only medium-warm at 75 centimetres down鈥攑robably
something around 13 掳C or a little cooler would be my guess. If Fluffy鈥檚
body is in your garden, it鈥檚 probably nicely moist, but if he鈥檚 in unwatered
soil the decomposers鈥� work will be slowed down quite a lot, because I know our
region hasn鈥檛 received enough rain to penetrate more than an inch or two this
summer.
If I bury a gopher in summer in this area, not as deep as Fluffy is buried
and not in a box, it won鈥檛 have become just bones if I accidentally dig it up
when working in my garden the following February, even though all the factors I
list above are at a high level here. That鈥檚 why I estimate that it would be at
least another six more months before decomposition occurs fully.
Some larger soil invertebrates may be able to help the box disintegrate and
also go to work on the body. Some eat meat, and some, such as dermestid beetles,
specialise in skin and hair. Vertebrate museums which prepare study specimens of
skeletons actually keep colonies of these beetles, to finish cleaning the bones.
They are also found fairly frequently on livestock farms like ours, and in
woodland where they help to clean up casualties.
And there are other invertebrate meat-eaters that live in the soil, such as
ants and worms and beetles. There are more in the upper layers than at the depth
that Fluffy is buried at, but some may get down that far.
There are a few other points. Eventually, even the bones will disintegrate
and feed the plants and the soil, although Fluffy鈥檚 teeth will be around the
longest鈥攖ooth enamel is a very durable material.
Also, the soil organisms often move bones around as they work on them. If you
dug him up, I wouldn鈥檛 expect to see a perfect skeleton of Fluffy, all in one
place, though you might be lucky because he has a box around him.
There is actually a centre on the East Coast of the US that is devoted solely
to studying how animal and human carcasses decompose and then disintegrate.
Forensic anthropologist Douglas Ubelaker describes it in his book Bones.
It seems that even scientists who specialise in old bones still don鈥檛 know as
much about the process as they would like to.
Molly
Northern California
Answer: The amount of time that it takes for an animal like Fluffy, or even a
human, to decompose to the point of becoming skeletonised is highly variable and
depends on many factors.
Those factors include, but are not limited to, the season of the year, the
ambient temperature and amount of rainfall, depth of burial, whether insects can
reach the body, the pH of the soil and whether the body was embalmed or
not.
The size of the body also plays a part in determining how quickly
decomposition occurs. Additionally, if a body is enclosed in a coffin, or
wrapped in plastic bags or carpet, for example, it will take longer to decompose
because it is protected. In Fluffy鈥檚 case, the depth of burial at approximately
75 centimetres, and the fact that he was buried in a cardboard shoebox, would
slow the process of decomposition. It is probable that Fluffy has not yet become
just bones.
Leslie Eisenberg
Board Certified Forensic Anthropologist
The State Historical Society of Wisconsin
Madison, Wisconsin
This week鈥檚 question
Thunk! Does beheading hurt? And, if so, for how long is the severed head
aware of its plight?
William Wild
Oxford
