One more possibility. I actually studied large asteroid strikes such as the KT Impact when I was an aerospace engineer. There were government funds to study the risk of impacts.

One popular hypothesis is that there is a large body out in the Oort Cloud that disrupts the orbits of icy bodies and sends them falling into the inner Solar System. Note that far from the Sun, it takes very little energy to put such a body into a parabolic orbit such as we see from comets.

There seems to be a periodicity to impacts. KT was about 65M years ago while there was another bombardment of Earth about 33M years ago.

If may be possible that very large objects such as a gas giant could be sent sunward on such a parabolic orbit. What would occur if such a large object hit the Sun as many comets do? Perhaps that could explain the evidence of rocks melting as the heat blast from the impact hit Earth.

BTW, you may note that we about due for another era of impacts, give or take a million years or so.

Don't stop digging and stocking your new bunker!