A 2,600-year-old human skull from the Iron Age was unearthed in a muddy pit back in late 2008. Upon closer examination, the soil-caked cranium contained an unusual yellow substance that turned out to be Britain’s oldest surviving human brain. Now, researchers have figured out how this remarkable brain had been preserved so well and for so long: The mud provided an oxygen-free burial.

The York Archaeological Trust was commissioned by the University of York to excavate in Heslington East for a planned expansion of the campus. The discovery of the skull—complete with a jaw and two vertebrae still attached—was made in an area that had been farmed and developed since at least 300 BC. As Rachel Cubitt from the trust was cleaning the skull, she noticed something loose inside. “I peered though the hole at the base of the skull to investigate and to my surprise saw a quantity of bright yellow spongy material,” Cubitt recalls in a news release. “It was unlike anything I had seen before.”

more details can be found here:  http://www.iflscience.com/brain/how-mud-helped-preserve-human-brain-2600-years