1st Year Geo. Question

[boneill@shellus.com]

  CORY WALTER wrote:

>How have geologists determined that the number of days in the 
>       year has shortened over time?

 I don't recall the reference, but one of the lines of evidence was the
daily tidal "banding" present in some Paleozoic corals.  If I remember
correctly there are incremental layers added which are bundled into
monthly groups and further separated into annual "bundles."  Counting up
the number of daily layers within a annual bundle they came up with
something like 410 days in a Devonian year (I think).   The explanation
was the the tidal friction in the Earth/Moon system was slowing the
rotation of the Earth resulting in fewer days per year.

  Hope that helps.

    Brian

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