[D Rider]

Wait a minute - aren’t those layers dated by the fossils contained therein, which in turn are dated by the layers in which they’re found?

You are correct, that is why the start of formation date did not change. Ignore the circular reasoning, in the end it will hurt you.

[BubbaBasher]

Ignore the circular reasoning, in the end it will hurt you.

Better phrased: "In the end it will come back to bite you".

[mnehring]

Exactly, it doesn’t change the start date, the study is just on the rate of formation. We have a lot of physical and chemical sign posts as to the overall date of rocks. As I pointed out above this, it is a pretty minor recalibration in the big picture of things. A few million years of formation time in a ~420 million year old rock.