The idea that oceans will evaporate refers to a scenario where Earth's oceans turn into vapor due to extreme conditions, such as severe global warming or the Sun's future expansion. In the distant future, as the Sun becomes hotter, it could cause temperatures to rise to a point where the oceans evaporate. Additionally, if Earth loses its atmosphere, water could no longer remain in liquid form, accelerating evaporation. This is a long-term event, expected billions of years from now.