Final answer:
Evidence that would most directly contradict our current model of Earth's ocean and atmospheric formation is if celestial bodies like comets and asteroids did not contain ice.
Step-by-step explanation:
The current model for how Earth's oceans and atmosphere formed suggests that water and gases were introduced to Earth both from internal sources, like volcanic outgassing, and from external sources, including impacts by comets and asteroids. The most direct piece of evidence that would contradict this model would be if comets, meteoroids, and asteroids in the solar system were found to contain no ice. Such a discovery would challenge the current understanding that these celestial bodies significantly contributed to Earth's water supply through impacts during the planet's early history.