Hi
here is one way:
>apply the write on effect on a solid(same size as your earth layer)=> Paint style=On Transparent
>Expression for Brush position
frame=timeToFrames(t = time + thisComp.displayStartTime, fps = 1.0 / thisComp.frameDuration, isDuration = false);
period=6;//creates dots every 6. frame
seed =Math.floor(frame/period)
seedRandom(seed, 1);
random([0,0],[thisComp.width,thisComp.height])
>apply CC Sphere