Answer:
New information is discovered that contradicts the existing theory.
Step-by-step explanation:
A theory is tested and the observation may confirm or contradict the theory. When the results of newly conducted tests confirm the theory, then the theory reaches a consensus in the scientific community. After conducting tests if new observation emerges which adds new information about the existing theory then it is revised. However, if new data keeps emerging that contradict the existing theory it will be rather than revised.