According to quantum mechanics, there is a non-zero probability for particles to tunnel through potential barriers, even if they do not possess sufficient energy to overcome the barrier classically. This phenomenon is known as quantum tunneling.
In the case of an atom in a solid, such as a piece of rock, the atoms are bound within the crystal lattice by the electromagnetic forces between them. Quantum tunneling allows for the possibility that an atom can overcome the potential energy barrier and escape from the solid, even if it does not possess enough kinetic energy to do so classically.
However, it is important to note that the probability of such an event occurring is extremely low for large barriers and heavy particles like atoms. The tunneling probability decreases exponentially with the width and height of the barrier. In the case of a solid, the binding forces between atoms typically create a potential energy barrier that is large enough to make the probability of an atom tunneling out negligible under normal conditions.
Therefore, while quantum tunneling is a real phenomenon, the probability of an atom in a solid tunneling through the barrier and escaping completely is exceedingly small and can be considered practically impossible in most cases.