Re: Age of the Earth

"George Prehmus" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> Joseph Lazio <[EMAIL PROTECTED]> wrote in message
news:<[EMAIL PROTECTED]>...
> > >>>>> "GP" == George Prehmus <[EMAIL PROTECTED]> writes:
> >
> > GP> I understand that geologial dating is done by comparing long
> > GP> halflife radioactive elements in rocks.  The data so gotten shows
> > GP> the time since the rock last was molten.  The formation of the
> > GP> Earth is supposedly determined by this method as 4.6 BYA.  Yet I
> > GP> undestand that the giant impact which caused to formation of the
> > GP> Moon occurred at about 4.3 BYA.  When that happened, I understand
> > GP> that the entire surface of the Earth was heated to the melting
> > GP> point, resetting the Earth's atomic clock.

<snipped explanation>
>
> Thanks. That was a help, but OK, so where did I go wrong? Was the heat
> of that giant impact not enough to reset the clocks?
> George

Hi George,
I'm not a geologist, but AIUI the oldest rocks found on earth are only about
3.8GY old. All other rocks have been recycled since then. The 'clocks' may
well have been reset at that time, but that was 500MY before the oldest
rocks we can use for dating today.

A very quick google on "oldest earth rocks" came up with
http://www.madsci.org/posts/archives/feb2000/951857637.Es.r.html

As far as I know, the date of 4.5GY or 4.6GY for the solar system comes from
meteor samples.