Outline Meselson and Stahl's experiment

They first grew bacteria in nitrogen-15 for several generations they then grew the same bacteria in nitrogen-14 for one generation the DNA from the bacteria got extracted After centrifuging the DNA they found 1 bar with a mix of heavy and light DNA after centrifuging the second time, 2 bars containing only light DNA and heavy-light DNA this gave evidence that the conservative and dispersive models were not correct and only the semi-conservative model applied