Meanwhile, the dust cloud generated by the impact would have blocked out the sun — likely triggering a “nuclear winter” and seeing temperatures plunge, acid rain falling from the skies and 75 percent of living species wiped out. …
So who won, the warming or the cooling?
Sounds like that old Steven Wright bit: "I bought a humidifier and a de-humidifier. So I kept them both on overnight and let them fight it out."
Interestingly an impact of this nsize would cook then cool the planet. Obviously the impact would generate tremendous shock heating and flash fires over a few thousand mile radius. Every forest within line of sight of the couple of hundred mile high fireball would instantly burst to combustion think nuclear fireball times a few million powers. Then materials would be vaporized and propelled into ballistic trajectories at all velocities from suborbital to earth escape. Those with suborbital would complete their ballistic arcs and start to reenter the atmosphere thousands of miles away in every direction like billions of ballsitic icbms reentering at mach 20+ every one would glow intensely with infrared energy this glow would be so bright that everything combustible under the path instantly combusts again every forest goes up in flames now over a 3 to 6 thousand mile radius. There’s still plents of material at orbital velocity spreading outwards that will over the next few hours slow down just enough to reenter on the opposite side of the planet and pretty much everywhere in between again the radiant heat of reentery reaches hundreds of degrees at ground level while not starting fires it literally cooks the foliage killing the plants and also any animals not seeking shelter underground, water or dense forest canopies. All the global fires add particulates to the upper atmosphere along with all the dust from reentry the net affect is the reduction of sunlight able to penetrate leading to massive global cooling and the total shut down of photosynthesis this is the global killer. Over the next few years the remaining orbital materials come down adding more particulates to a dark cold world. It will be decades if not hundreds of years before the levels of sunlight return to preimpact intensity at ground level. So in the end it was fire, more fire then decades of cold that caused 80+% of all species to die off at the KT boundary. The global reentry of materials is readily confirmed by the layer of iridium at the KT boundary in the global rock record. Anywhere on earth at the KT boundary that Ir layer is found. Ir is exceedingly rare on Earth in crustal materials its one of the rare earth elements named that for a reason. The only way to get a global deposit at high enrichment is by deposition from a space impactor which a good number are enriched in Ir. Volcanic activity doesn’t have the ability to put up a global layer.