<P> The inventory of carbon - 14 in Earth's biosphere is about 300 megacuries (11 E Bq), of which most is in the oceans . The following inventory of carbon - 14 has been given: </P> <Ul> <Li> Global inventory: ~ 8500 PBq (about 50 t) <Ul> <Li> Atmosphere: 140 PBq (840 kg) </Li> <Li> Terrestrial materials: the balance </Li> </Ul> </Li> <Li> From nuclear testing (till 1990): 220 PBq (1.3 t) </Li> </Ul> <Li> Global inventory: ~ 8500 PBq (about 50 t) <Ul> <Li> Atmosphere: 140 PBq (840 kg) </Li> <Li> Terrestrial materials: the balance </Li> </Ul> </Li> <Ul> <Li> Atmosphere: 140 PBq (840 kg) </Li> <Li> Terrestrial materials: the balance </Li> </Ul>

When is the radioisotope carbon-14 formed in the atmosphere