tidal bulges (again!) from Earth and Sky

[Larry Smith <Larry.Smith@snow.edu>]

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> Wednesday,  April 23, 1997
> TIDALITES
> If you're one of those people who's always wishing for more hours in a
> day, you can get them -- if you can wait a few hundred million years.
> Evidence that Earth's day is getting longer -- after this on Earth and
> Sky.
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>
> DB:  This is Earth and Sky.  Scientists have known for a long time that
> the moon is edging away from Earth.
>
> JB:  The moon is known to be receding from Earth at a rate of about four
> centimeters -- about an inch and a half -- every year.  Related to the
> receding moon is the slowing of Earth's rotation.
>
> DB:  Both processes happen because of the moon's gravitational pull.
> The moon's pull creates two "tidal bulges" on Earth -- one on the side
> of Earth facing the moon, and the other on the opposite side.  These
> bulges of ocean water aren't exactly aligned with the location of the
> moon, though -- because they're carried along with Earth's rotation.
> The moon tries to pull the bulges back into alignment with itself, and
> it's this pull that slows Earth's spin on its axis -- and causes the day
> to get longer.
>
> JB:  Last summer, scientists published a study of rare sedimentary rocks
> containing records of ancient tides.  Analysis of these "tidalites," as
> they're called, reveal just how much faster the moon used to orbit
> around Earth.  This information can then be used to show exactly how
> much shorter days on Earth used to be.  Nine hundred million years ago
> -- as far back as the record goes -- a day on Earth appears to have been
> only about 18 hours long.   Just a reminder -- we have information on
> National Science and Technology Week at our web site --
> www.earthsky.com.   We're Block and Byrd for Earth and Sky.
>
> http://www.earthsky.com/1997/es970423.html
>
>
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