3.8 million year old egg white

Scientists have successfully extracted proteins preserved for nearly 4 million years in ostrich eggshells.

Recovered from sites inhabited by ancient human ancestors in Tanzania, and dated accordingly, the fossilised eggshell samples have yielded traces of the original protein deposited into the egg by the parent bird. 

According to York University archaeologist Matthew Collins, who has just announced the discovery in the journal eLife, "This story has been 21 years in the making!"

The discovery paves the way for understanding how biological remains may be preserved in a range of fossil contexts and for how long.

Collins and his colleagues used the eggshell remains because they came from sites that had been well documented and carefully dated. "So we knew, reliably, how old this material was."

The samples were first chemically brutalised with bleach to strip the outsides of any contaminating proteins.

"There's so little of the original stuff still there that recent material coming in from the environment can complete overwhelm the signal."

Once the samples were cleaned they were ground up. "They actually smelled bad, like rotten eggs, because the stuff was so old," explains Collins. The samples were fed into a mass spectrometer, which can tell apart molecules on the basis of their sizes.

The traces that emerged showed unmistakeably the presence of the proteins struthiocalcin-1 and 2, two dominant molecules present in bird eggshell. And by reading the sequence of amino acid building blocks from which the proteins are constructed it has been possible for the team to deduce the genetic code that the original bird used, millions of years ago, to make them.

"Although when we read the ostrich sequence from 4 million years ago it was the same as a modern day ostrich, so not very exciting in that respect," laughs Collins.

The key finding in the paper is that although proteins can be quite fragile in nature and fall apart readily, a team of chemists working in parallel with the York team had predicted that certain minerals in the eggshell would have a stabilising effect on the nearby protein, helping to preserve it.

"So this is a really neat proof of the theoretical modelling too."

Critically, although these eggs were laid 3.8 million years ago, the severe conditions in which the material has existed over that time, including fierce heat and drying in the African Sun, means that similar material deposited in a cooler area of the planet could be expected to last over 16 million years, or a third of the way back to a T-Rex!

The work is important because it highlights how proteins can be preserved in fossil remains, and under what conditions. If the team can get this working reliably and safely, then, unlocking the genetics of our early ancestors could be tantalisingly near...