I don't think a 77 foot asteroid would do too much damage, especially if it hit the water.
You underestimate the power of asteroids. The one that killed the dinosaurs (and virtually everything else on earth larger than a rat) was only 6 miles in diameter. (and hit water; specifically, the gulf of Mexico.) 77 feet is about 1/400th that size, but 1/400th of the end of the world is still pretty f*cking scary.
I don't underestimate the power of an asteroid. I know how much damage that they can do. But 77 feet compared to 31,680 feet is quite a difference. So yeah sure, a 77 foot asteroid is gonna kick up some dust, and possibly f*ck some shit up - but odds are that it will land in water.
Now, I didn't realize that the great asteroid landed in the Gulf Of Mexico, but I've heard of that before. I wonder how that covered the Earth in a shroud of darkness, maybe it hit a shallow spot, I dunno.