Posted: Mar 31, 2010 8:21 pm
byofrcs wrote:Beelzebub wrote:OK, here's a question - why should the Earth contain any radionuclides at all?
Do we know what proportions of isotope to parent element are created in a supernova explosion (assuming, for now, that that is where they originate from) ?
If a supernova occurred, say, 4 billion years before the Earth formed, then wouldn't all but the longest-lived isotopes have decayed by then? Is it legitimate to consider the supernova as being contemporary to the formation of the Earth?
Just asking, as I'm sure others have thought of similar questions...
No. The initial Big Bang formed quite light weight elements and isotopes. Subsequent stellar nucleosynthesis formed all the heavier elements. The thing is that we're dealing with half-lifes and these are a binary progressions not straight-line reductions.
I used radon gas as an example to show the perversity of creationism but the most unusual is for 209-Bismuth which has a proven half-life of 1.9 × 1019 years - or roughly a billion times longer than the current age of the universe.
The U-238 to Th-234 has a halflife of 4,460,000,000 years so if at about 4 billion years ago you had 1 ton of U238 then now you would have about 1/2 a ton. Then in another 4 billion years you would have 1/4 ton and then so on for trillions of trillions of years into the future until the last Uranium atom split (more or less).
The current understanding is that the earth's core is hot mainly because of radioactive decay and of these Uranium is the most important. By looking at the ratios of uranium-238 and uranium-235 on Earth and as these have different halflifes then by comparing the ratios with what is calculated to be the ratios in supernova we can calculate, as a rough guess, that the Uranium on Earth dates from a supernova about 6.5 billion years ago (so about 2 billion years before the Earth was formed) though the actual picture if we look at all elements is that the Earth, and so each of us, contains elements formed in a number of supernova.
This message was brought to you from the You-are-but-an-insignificant-mote-in-the-universe Ministries.
Ah, but the 'Big Bang' doesn't enter into it - it only produced H, He and Li - all the elements we are addressing come from nucleosynthesis in stars and supernovae!
Now, my argument would be this - assume an ancient universe, billions of years old, but a young Earth (some 6000 years old) - now, if the supernovae that produced the heavy elements, and their isotopes, exploded 2 billion years before the Earth formed then all the elements listed by Calilasseia would have decayed already. So the creationists, if they can stomach an old universe, could make a case for a radiologically consistent young Earth!!
Of course, there are other evidences for an old Earth, but, at least at a superficial level, radiological dating doesn't necessarily mean an old Earth
