YOu mentioned in your profile that you “held one of the oldest things on earth at half a billion years old”. What was

Question: YOu mentioned in your profile that you "held one of the oldest things on earth at half a billion years old". What was this?
- Keywords:
  hold,
  oldest
Asked by kingm to Dave on 12 Mar 2015.
- Dave Bond answered on 12 Mar 2015:
  
  It was an asteroid, so as something that was not part of earth but fell to it. It would be considered one of the oldest, but if you think of the rock earth is made from it would be quite young. Earth is 4.54 billion years old.
  
  It was cool though, and very heavy.
  
  Have a look here
  http://www.quora.com/What-was-it-like-to-live-on-Earth-half-a-billion-years-ago
  
  Earth was quite differet then.

Question: YOu mentioned in your profile that you "held one of the oldest things on earth at half a billion years old". What was this?