The oldest chicken egg with an intact shell was discovered in Israel at the site of an ancient city called Yavneh.
The egg was complete with most of the shell intact except for a few cracks. The interior contents of the egg had leaked out but a part of the yolk was left behind.
Researchers were amazed at the unique discovery because most eggs from ancient sites are fragmented and broken and are usually never intact.
Egg shells are especially fragile and can be brittle. The shells are primarily composed of calcium carbonate and can easily dissolve in substances like vinegar which contain acetic acid. The strength of the egg shell depends on several factors including the health of the chicken that laid the egg.
Researchers believe that the egg found at the ancient site remained intact only because it was preserved in human waste. The human waste which might have involved fecal matter created oxygen-free conditions which prevented the egg and its outer shell from decaying.
After the egg was recovered from the site, its shell cracked further, but researchers pieced it back together in the lab.
The discovery of the intact chicken egg is an indication that the ancient Jews and Muslims who lived in the area at the time included it as a part of their diet. Chickens were first kept as domestic animals about 6000 years ago in Southeast Asia and then a few thousand years later, chickens and their eggs were added to the human diet.