Final answer:
Meselson and Stahl's experiment supported the semiconservative mode of DNA replication.
Step-by-step explanation:
Meselson and Stahl conducted an experiment to determine the mode of DNA replication. They grew E. coli in a medium with a 'heavy' nitrogen isotope (15N) and then switched it to a medium with a normal nitrogen isotope (14N).
By using density differences, they found that after one round of replication, the DNA sedimented halfway between the position of 15N and 14N, ruling out the conservative model. After the second round of replication, they observed two bands, one at the intermediate position and one at the 14N position, supporting the semiconservative replication model.