[blam]

The earth has a thicker atmosphere so the impact to the earth would be less than it would be to the moon. Right?

[Lokibob]

yep, with no atmosphere, the moon got the full effect.

[RightWhale]

the object that struck the Moon was about 300 metres across

There is a point on the mass scale, probably less than even this size, where the atmosphere can't slow the object appreciably, nor heat it so it fragments or explodes during the short time the object is inside the atmosphere. The result would be about the same on the earth or on the moon for the big meteorites.

[johnny7]

Yeah... we just all go to work in the dark and come home in the dark for the next 500 years.