If they remain coherent, 100-m bodies pass through atmosphere at cosmic velocity.
But many break up due to "ram pressure" P=ρv2, whereρ=densityofair,v=speed.
e.g.ρ=1kgm-3,v=30km/s=3x104 m/sthenP=109 Nm-2 but 1 atmosphere = 1 bar = 105 N m-2,so,P = 104 bar
This like being hit with a hammer, and the body breaks if not strong.
Then, the subsequent interaction is between air and the fragments, which can fragment again and again, until the particles are so small they can be stopped by friction.
result: atmospheric explosion