Carbon-14 forms in the atmosphere from nitrogen-14 by:

1. Nitrogen-14 has seven protons and seven neutrons. 2. Carbon-14 has six protons and eight neutrons, so one proton must become a neutron. 3. Carbon-14 is a naturally occurring radioisotope created in the atmosphere from atmospheric nitrogen-14 by the addition of a neutron and the loss of a proton because of cosmic rays. 4. Cosmic rays supply the energy for that conversion. _Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 2 'The Chemical Foundation of Life', sections 2.1-2.3_