A collision between a 3-kilometer ball of steel and the Earth would have catastrophic consequences. The specific effects would depend on several factors, including the speed of the collision, the angle of impact, and the location of the impact.
However, in general, a collision of this magnitude would release an enormous amount of energy. The impact energy would cause a massive explosion and generate a powerful shockwave. The immediate effects would include:
Crater Formation: The impact would create a crater of significant size, likely several kilometers in diameter and hundreds of meters deep. The exact size and shape would depend on the factors mentioned above.
Ejecta and Debris: The impact would eject a tremendous amount of material into the surrounding atmosphere. The ejected debris would form a plume of dust, rocks, and molten fragments that would be launched high into the atmosphere and possibly even into space.
Shockwave and Air Blast: The impact would generate an intense shockwave that would propagate through the atmosphere. This shockwave would cause widespread destruction in the surrounding areas, leveling forests, shattering buildings, and causing severe damage over a large radius.
Global Effects: The magnitude of the impact would likely have global consequences. The massive release of energy would send a significant amount of dust and debris into the upper atmosphere, potentially leading to a temporary darkening of the skies and a decrease in sunlight reaching the Earth's surface. This could have long-lasting effects on the climate and ecosystem.
It is important to note that a collision of this scale is extremely rare. Earth is protected to a certain extent by its atmosphere, which burns up many smaller objects before they reach the surface. However, larger impacts have occurred in the past, leading to significant changes on Earth and even mass extinctions.