Final answer:
Meselson and Stahl used equilibrium density gradient centrifugation to distinguish between heavy or light DNA and found that the DNA formed bands according to its density in the gradient.
Step-by-step explanation:
The scientists who used equilibrium density gradient centrifugation to distinguish between heavy or light DNA were Meselson and Stahl. They performed an experiment with E. coli bacteria grown first in heavy nitrogen (¹5N) and then in light nitrogen (14N). During density gradient centrifugation, the DNA was loaded into a gradient of cesium chloride and spun at high speeds. The DNA formed bands according to its density in the gradient, with DNA grown in ¹5N forming a band at a higher density position than DNA grown in 14N. Meselson and Stahl observed that after one generation of growth in 14N, the DNA formed a single band that was intermediate in position between the ¹5N and 14N DNA bands, suggesting a semi-conservative mode of replication.