Naked Science Forum

Life Sciences => Physiology & Medicine => Topic started by: annie123 on 06/02/2013 02:22:31

Title: Why do bones survive intact for so long in the ground?
Post by: annie123 on 06/02/2013 02:22:31

I have seen many programmes talking about bones found in many different locations to be many thousands of years old. How is it that bones can stay in one piece for so long? If one is buried in a coffin would the bones stay like that for ever?

Title: Re: why do bones last so long?
Post by: evan_au on 06/02/2013 11:08:22

The most likely way for bones to be preserved is if they are quickly buried, so wild animals can't chew them and scatter them. Animals falling into limestone caves sometimes have their skeletons enclosed in limestone deposits.

It helps if the bones are quickly buried in conditions which stop bacterial action, such as ice, or oxygen-deprived sediments at the bottom of a lake, or extremely dry conditions in a desert. Icy conditions can even preserve some of the soft tissues of a body, as well as the protein in the bone - maybe one day someone will resurrect a woolly mammoth!

But the fact is that most bones are quickly destroyed or lost - by animals, by fire, water or chemical action. Only a small fraction are preserved - and humans might be increasing that ratio by quickly burying bodies underground.

Even in the near-lefeless deep ocean, dead whales are quickly consumed by creatures which converge on the dead body - including worms which specialise in digesting bone, see http://en.wikipedia.org/wiki/Osedax

Title: Re: why do bones last so long?
Post by: cheryl j on 06/02/2013 16:55:34

Teeth last even longer than bones because enamel is harder, dissolves less easily than bone minerals.

Title: Re: why do bones last so long?
Post by: evan_au on 07/02/2013 09:39:33

After death, and deprived of its resilient protein skeleton by bacteria, bone is quite brittle.
After many years, bones are likely to crumble when handled roughly, or if exposed to blowing sand.

As Cherylj points out, often a tooth is the only recognisable part left of a skeleton - perhaps because it is hard enough to pass through the gut of a hungry scavenger, relatively unscathed.
 
The fossils we see in museums have their protein skeleton replaced by silica or other minerals carried in by groundwater. This is much heavier, harder and more durable than the original protein and calcium-based composition (but also more likely to shatter if you drop it).