Originally posted by trueperspective
reply to post by Trudge
Please tell me how you know for a fact that the Earth is billions of years old?
The age of rocks is usually determined by radioactive (or radiometric) dating. Some elements are radioactive and gradually convert from one isotope to
another. For example, uranium 238 (238U) will gradually convert to lead (206Pb). It will do this at a constant rate. The rate is described as a
half-life of the isotope in question. This is the period of time it takes for half the atoms of 238U to convert to lead. For this particular element,
the half-life is 4.47 billion years and uranium/lead dating is useful for rocks between 1 million and 4.5 billion years (as luck would have it!).
Other elements are also used (potassium/argon for example). The choice of element depends on how widespread it is - if it isn't found in many rocks
then it's not very useful. And how long the half-life is - if the half life is shorter than the age of most rocks then its equally unuseful.
Radiometric dating can only be performed on igneous rocks. The uranium/lead elements are most often used because igneous rocks often contain uranium
and the half life is so long. The oldest rock found is around 4.54 billion years old. This is consistent with the age of rocks from the moon and from
meteorites, which all point to an age around 4.54-4.56 billion years.
Separate studies of the sun's mass and luminosity suggest that the solar system itself can't be much older than these rocks.
All of this is well-known scientific information. The arguments against it lack scientific credibility, and most of them are posted by so-called Young
Earth Christians. The vast majority of the scientific community accepts as valid the information provided by radiometric dating. The claims made about
"assumptions" in radiometric dating of billion-year old rock are actually stepping stones that those who work in the field have worked hard to
eliminate as impediments to the accuracy of their measurements. Making a "claim" about any aspect of radiometric dating without scientific proof
that something is wrong, as has been done, does not invalidate the work - or the mearurements. The earth is about four and a half billion years old.
Here is the link.....
wiki.answers.com...
[edit on 11-3-2010 by Trudge]