[VadeRetro]

Thanks. It looks like one paper by Schopf may touch on the issue.

[RadioAstronomer]

Placemarker :-)

[Alamo-Girl]

Thanks for the link! That is the kind of combination of evidence he mentioned briefly in the above linked article. Seems to me that finding agreement on the system of measures to be used would be helpful to all of them.

Here's another interesting one: Determining the Biogenicity of Residual Carbon within the Apex Chert