As the object was caught by Earth, it fell down at tens of km per second to the ground, exploding on impact. The models made of Chicxulub suggest that the energy released was something like 1025 joules in one minute. The immediate effect would be the vaporization, melting and ejection of the original meteorite, millions of liters of water and about 200 cubic km of Earth's crust. There would be an immense heat and pressure wave, and giant tidal waves would rush from the impact site, speeding into inlands possibly hundreds of kilometers, causing the floods seen in the bottom part of the K/T sediments. As the rocks of the area of impact had high amounts of sulphides, their vaporization would release a lot of sulphur into the atmosphere, and along with the oxidized atmospheric nitrogen it would cause major acid rains, changing the pH of the surface waters. This kind of chemical reactions have been found in the K/T boundary layer.
The ejected melted rocks fell down around the world (as much as 10kg/m2 has been suggested), causing major forest fires, and thus creating the soot found in the sediments. The vaporized rock material and dust-sized grains of the ejecta would stay up in the atmosphere for periods up to 2-3 months causing darkness and cooling of the weather and eventually creating the upper fireball layer in the sediments.
And, finally, the impact would have released something like 1015-1017kg of CO2 into the atmosphere, causing major greenhouse effects. The upper limit of this carbon dioxide would have been about 50 times as much as found today in the atmosphere, and would have warmed the atmosphere by 15oC. This amount of CO2 would have taken over 100 years to be removed.
