[vmelkon]

Is it generally accepted that the way that C14 forms is that N14 in the upper atmosphere gets hit by a neutron, which causes a proton to be released, thus N14 turns to C14.
Isn't it more likely that C13 gets hit by a neutron and C14 forms.
Also, C12 gets hit by a neutron and C13 forms, thus preserving the amount of C13 and even increase it.
It might explain why there is 1% of C13 in natural Carbon.

Also, apparently coal doesn't have much C13. It is nearly all C12 and people think that coal is just ancient plants and trees.