What would happen to the earth if the moon lowered to half of its present distance?

Partial lunar eclipse

This happened already!
Well, not exactly lowered. It just was lower.
The moon is actually drifting away from us at an astounding and measurable rate every year. One day it will fly away and that will be very bad for Earth.
The moon is drifting away from us at a rate of 3.78 centimeters (1.5 inches) per year, and that distance is measurable with laser instruments.
That is a tremendous amount. In your life the moon has probably drifted a foot or more away. Conversely, there was a time when the moon was much closer.
Take 1.5 inches and multiply it by millions or billions, and it starts to add up.