are now made synthetically.Carbon-14 is formed in upper layers of the troposphere and the stratosphere, at altitudes of 9-15 km, by a reaction that is precipitated by cosmic rays.. 
Ó gbajúmọ̀ fún àwọn ìrìnàjò rẹ̀ àti Úunkèrindò rẹ̀ ní Áfríkà àti Asia àti ìmọ̀ rẹ̀ nípa ọ̀pọ̀ àṣà àti èdè.. 