Objects of this size punch through the Earth's atmos phere as if it wasn't there at all. The Earth has been cratered as much, if not more, than the Moon . Such an impact would trigger global fires and fill the atmosphere with dust which would take years to settle out. The change in global temperature would lead to the collapse of the ecosystem and widespread extinctions. Such an event probably led to the extinction of the Dinosaurs at the end of the Cretaceous period.
Iridium is rare on Earth and plentiful in meteorites.
In a more positive light, this event may have permitted the emergence of the mammals as the predominant species on the Earth. Cosmic forces have influenced the progress of the evolution of life on Earth. Such an object would moderately alter the climate disrupting agriculture. Such impact happen every 10,000 - 100,000 years. The manner in which solar systems form suggests that impacts are a factor on planets everywhere in the universe.