Exopaleontology?

This article talks about an Arizona State University professor Jack Farmer and his idea that looking for traces of life on Mars is best done looking for "past life, preserved as 'biosignatures' in old rocks" with current technology. Because we are unable to drill to the depths required to find any possible liquid water, he says that searching for traces of former life, or exopaleontology as he calls it, is the path we must follow for now until technology advances to allow us to dig thousands of feet down into Mars.