Plants fix atmospheric carbon during photosynthesis, so the level of 14 C in plants and animals when they die approximately equals the level of 14 C in the atmosphere at that time. Carbon may also be produced by lightning bolts   but in amounts negligible compared to cosmic ray production. Decay chain of carbon Over the years, other secondary radiocarbon standards have been made. Retrieved from " https: The INTCAL13 data includes separate curves for the northern and southern hemispheres, as they differ systematically because of the hemisphere effect.
How Carbon-14 Dating Works
Retrieved from " https: Concepts Deep time Geological history of Earth Geological time units. Three separate laboratories dated samples of linen from the Shroud in ; the results pointed to 14th-century origins, raising doubts about the shroud's authenticity as an alleged 1st-century relic.