Why bones are not degraded ?

Why bones are not degraded ?

Whenever I read articles about archaeological discoveries, I often come across skulls, bones, and burials. I wonder how bones can survive without degrading for 1,000 or even 2,000 years. This curiosity led me to learn a few fascinating facts about bone preservation, which I would like to share in this blog.

Do bones really not degrade? This is the first and most important question to ask.

The answer I found is: yes, bones do degrade. But then, how are we able to find perfect skeletons or parts of skeletons in some burials? Before answering this question, one must understand bones themselves. Let’s dig deep!

Bone is a composite material and is made of a mineral and organic part. The mineral and organic components are interlinked with bone structure and will provide important properties like strength and elasticity. Damage to one component will weaken the other.

The building blocks of bone are mineral plate shaped crystals of carbonate , with varying ratios of calcium and phosphorous and additional ions such as silicon and zinc.

During life, bone can accommodate and exchange chemical elements through substitution with those usually present in the body. This is important in living people because our skeletons are used to store essential minerals. After death, these qualities remain and the bone is still reactive – meaning that bone will constantly change over time, even after you die.

Change that undergoes during life is called biogenesis whereas,change after death is called diagenesis.

Now, let us come to the question: How can a skeleton survive for many thousands of years?

One of the most important factors influencing bone diagenesis after burial is the local burial environment, such as soil conditions and groundwater movement. Bones tend to survive well in alkaline soils, whereas they are more readily destroyed in acidic soils.

Acidic soils quicken the diagensis process of bones

This may be one of the reasons why burial practices differ around the world according to their environment. Especially in Tamil Nadu, India, we find different types of burial practices: coastal and riverine regions commonly practiced urn burials, inland and forest regions practiced dolmenoid and cist burials, and in northern Tamil Nadu, we find a mix of burial types.

This is a major reason why urn burials were widely practiced in southern Tamil Nadu, a region historically affected by repeated river-flood events. In response to their environment, communities developed innovative urn-burial practices. A prominent example is the Adichanallur urn burial site, situated near the Tamirabarani River. The presence of only skeletal remains, with no evidence of soft tissue, suggests the practice of secondary burial.

Bones inside the urn - Adichanallur

So, bones do degrade, but the process may take thousands of years when they are buried in alkaline soils, dry arid environments, or intentionally preserved by ancestors. Therefore, it is not incorrect to say that burials and cemeteries functioned as ancient preservation methods for protecting human bones.