Work-Energy principle: Doubt regarding zero initial velocity assumption

I have a basic doubt from engineering mechanics. We have the work-energy principle stating that the work done by the forces acting on a partile is equal to the change in kinetic energy of that particle. However, the kinetic energy is a qudratic function of the velocity of the particle, and hence the change in kinetic energy for a given change in the velocity would depend on the initial velocity of the particle, before the work is done by the forces acting on it. In this scenario, how are we justified in assuming a particle at rest on earth to be having zero velocity, for the purpose of applying the work-energy principle? In an absolute sense, the velocity of the particle is not zero due to various kinds of motions the earth is having. Any direct answer or hint for arriving at the answer would be helpful.