Billy was playing video games when he rotted his brain.
The soft parts of his body slowly rotted away until all that was left were his bones.
Finally, his house collapsed on him and the rubble was compressed. It became sedimentary rock. As his bones decomposed, minerals filled in the space the bones had left in the rock and created a cast of the original fossil.
101.45 billion years later the Pandas, who had taken over the world, found him in a mining expedition.
Scientists figured out that the fossil was a cast of the original organism, and used relative dating to find out that the fossil was from the Quaternary period.
It was then put on display at the new Museum of Human History.