What Happens to Human Remains Many Years After Cremation?
When a human body is cremated, the organic matter is burned away, leaving behind bone fragments composed primarily of calcium phosphate. Over many years, these remains undergo changes but largely retain their chemical structure when buried in a sealed urn. The inorganic compounds may slowly dissolve if exposed to the elements, but otherwise remain stable.
When a human body is cremated at high temperatures reaching 1000°C (1832°F), the organic matter is turned to ash. What remains are bone fragments, composed mainly of a mineral called calcium phosphate along with small amounts of other compounds like sodium, potassium, zinc, and carbon.
Immediately after cremation, these remains are a pale grayish-white color, not stark white like often depicted in movies. The fragments are then mechanically processed into a finer powder referred to as “cremains” or more commonly “ashes.” A full adult cremation will yield about 3-5 pounds of ashes.
So what happens to these ashes over time? It depends largely on what is done with them. When placed in a sealed urn and buried, the ashes can remain chemically stable for surprisingly long periods of time, even centuries. Calcium phosphate is quite insoluble in water and unreactive to oxygen at ambient temperatures. Sealed away from the elements, it does not significantly decompose or change form.
However, if the ashes are spread on land or at sea, environmental factors come into play. Water can very slowly dissolve the calcium phosphate over time. Soil acidity may also contribute to gradual dissolution. Plants can absorb and utilize the calcium, phosphorus and other trace minerals. In this way, the inorganic remains are eventually recycled back into nature.
Some have described this poetically - human remains nourishing new life and completing a natural cycle. The calcium phosphate and other minerals that give structure to our bones ultimately return to the earth, perhaps to be taken up into a tree or a flower. Ashes to ashes, dust to dust, as the saying goes.
In recent years, some have even transformed cremated remains into diamonds. This is accomplished by extracting the carbon and subjecting it to high heat and pressure, similar to conditions that form natural diamonds. Though symbolic, these “memorial diamonds” demonstrate the stability of the fundamental atomic components of our bodies.
Ultimately, while the organic, carbon-based molecules that animate life are fleeting and transient, the inorganic minerals have a permanence to them. When protected from the elements, human cremated remains can persist in a stable form for a very long time, leaving a lasting mark of our lives.