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Re: age of earth
>>Scott Horton posts:
>>"age of the earth is 4550 years old..."
Did I really say 4550 years? If I did, then what I meant, of course, is 4550
MILLION years old, I'm not a Creationist :)
>Gee, that's precise. I wonder how the extra 50 is determined since the
>oldests rx are ca. 3951 +/- about 100my (Isua Greenland) and we have some
>allochems in Australian rx perhaps 4.1 ga, moon rx dated ca. 4.5 ga +/-
>at least 100 my and some meteoric stuff with the same error factor.
> I teach students in my historical geology class that Earth is minimally
>4.5 ga but may be as old as 5.0 or more in a poorly consolidated form: I
>believe noone has more precise data. I'd be curious if Scott knows of
>sources I don't.
The earth of course is much older than the oldest rocks here (radioactive dating
methods determine the age of the rock since solidification, and the earth was
molten during its accretion phase). The age I quoted was one agreed upon by some
committee (sorry, I don't remember the name of it, it was during my university
training a dozen years ago, and may need to be revised). I believe it was based
mostly on meteoric material, and agreeing with solar evolution models and
planetary accretion models. Even if the error factor is +/- 100my, it is still
correct to state the mean value. ie. 4550 +/ 100my is more correct than round-
ing to 4500 +/- 100my. I did not mean to imply that the figure was accurate to
3 significant figures, and should have quoted the error factor (except I don't
remember what it was).
I have never seen estimates exceeding 4.6 Ga before. A figure of 5.0 Ga would
imply that it took all meteorite material 500 my to solidify (the oldest dated
material that I know of is 4.55 Ga). I could accept that only if all meteoric
material was once part of bodies >> 1000 km diameter (very unlikely).