Final answer:
The preservation of existing topography is not likely to occur after a 10 km diameter object strikes the Earth; instead, a crater, earthquakes, and possibly tsunamis would result, altering the landscape significantly.
Step-by-step explanation:
The event not likely to occur as a result of a 10 km diameter object striking the Earth is the preservation of existing topography. When a large meteorite impacts the Earth, it typically results in the formation of a large crater, along with the possibility of triggering earthquakes and tsunamis if it strikes near or in large bodies of water. The force of such an impact would significantly alter the landscape, making the preservation of the pre-impact topography very unlikely. The theory of plate tectonics relates to many Earth phenomena such as earthquakes, volcanic eruptions, and mountain building, all of which involve significant alterations to the Earth's surface, unlike the preservation of existing topography.