how do i make my modle solid?

hi i made a modle in blender and its a sphere with mountains all over it becuase its a planet but the problem is i just fall through it in unity i checked the generate colliders and have a capsule collider on my character and i still fall through it worked when the model was smaller for some odd reason but when i scalled it up i just fall throught it and i added mesh colliders and everything to the model. Im out of ideas can someone give me an idea to try thanks

Reduce fixed time step (Edit/Project Settings/Time) until the collision is detected.

thanks but i found out that when i imported my model from blender it also imported a animation componet for some odd reason and when i removed it the model was visible