Brother John said:
Just during my own lifetime they have repeatedly changed their estimates almost always claiming that the earth is much older than the last time they pretended to know. They obviously haven't got a clue.
I think that estimates of the age for the Earth from the decay of radioactive isotopes have been pretty stable for decades. What does seem to change all the time is the estimate of the age of not the Earth but the universe. This is because it's rather difficult to pin down the parameters in the equations that determine the age of the universe. Furthermore, when talking to popular audiences cosmologists have occasionally been somewhat glib about, for example, the relationship between redshift and distance and their deduction of the age of the universe from that relationship. But in my lifetime, at least, the estimates haven't varied by more than a factor of two or so. By the way, the universe is now thought to be somewhat younger than the estimate when I first started studying physics.
(To be fair, the estimate of the age of the Earth from Victorian times to today has varied by a factor of something like a thousand. The Victorians could estimate the age of the surface of the Earth by estimating the time it would take to cool from a molten state to its current temperature, but they got the answer wildly wrong because they didn't know about radioactivity and especially didn't know that radioactive decay in the centre of the Earth was keeping it warm. As an aside, in the 19th century, the Earth being only a few million years old was the strongest argument against evolution by natural selection as the generator of biodiversity.)
Rich _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
