> Some examples of what I mean about historical geology may help. A
>sample of sediment can be put under heat and pressure, and the resulting
>rock be compared with natural rocks to see if they encountered similar
>levels of heat and pressure.
Your use of the word "encountered" rather than the more scientific
(attitude) "may have encountered" is troubling, but I can write it off as
a careless mistake, since you didn't repeat it in the echinoderm example....