QUOTE (Irion @ Apr 26 2011, 12:03 AM)

Nope. They are assumed to be created by stars.
Our system is a population 1, meaning it is suspected to have been created by the shockwaves of nearby supernovas.
Thats the reason for all the heavyer elements found in our solar system.
If you go down this road you end up with population II stars (very few heavy elements) and the suspected population III stars directly after the big bang (with only traces of heavier Elements created by the big bang)
http://en.wikipedia.org/wiki/Metallicity#Population_II_starsSo stars breed all the elements out of the stuff(Mostly Hydrogen) from the big bang.
My bad, guess I got my facts screwed up.
QUOTE (Irion @ Apr 26 2011, 12:03 AM)

Here comes logic into play: Think of the half-life period of uranium 700 million years for uranium-235 period and 4.1 Billion years for uranium-238.
Big Bang was supposed to be 13 billion years ago. So how could there be any uranium-235 on this planet? (if it would only be created in the big bang)
13b/700m ~ 18
2^18 ~ 250k
0.0004 % of the original U-235 mass left in the universe (assuming no extra created).
earth is about 4.54b
4.54b/700m ~ 6
2^6 = 64
1.5% of whatever U-235 started out in this planet is left.
There wouldn't be much either way, but I see your point.