Path of dark reaction of photosynthesis was traced through the use of

The path of the dark reaction of photosynthesis was traced through the use of ¹⁴CO₂.
Calvin and his co-workers by using the isotope of C which is 14C to trace the path of the carbon fixation in light reaction. Due to his discovery, the cycle is known as the Calvin cycle (Dark reaction) which is the common path for all plants in photosynthesis.