a) A comet, b) an asteroid, c) the dust from two comets, or d) the debris from the collision of two comets.
The most common way these items formed is by collisions between comets.
In this case, it’s likely that the comet dust and the debris from two comets, plus the debris from the collision of two comets, collided about 5.1 billion years ago. This means that any asteroid or comet debris that may be left over from this event would have been around for only a relatively short time, but they were large enough to affect life on Earth.
This is the same type of collision that made the Earth and moon separated. Any debris from this event likely formed in the asteroid belt between Mars and Jupiter.
This is the same type of collision that made the Earth and moon separated. Any debris from this event likely formed in the asteroid belt between Mars and Jupiter.
A large asteroid or comet would have been about the size of a baseball. The energy from the collision may have been enough to cause the moon to fracture into pieces, and its dust to be blown out into space.
It is not clear if the moon was formed from the debris of the impact. It is also not clear if the moon and Earth were separated by that collision. If the moon and Earth were separated by impact, the collision can have been due to a large object, such as the asteroid that made the Earth and moon separated.
The collision is not clear from the information available. The first information is from the Wikipedia entry for Comet 67P, and it says that the collision was due to the collision of two very large objects, and that the two objects were moving at speeds up to 300,000 km/h (or more than 200,000 mph).
The two are both larger than a small asteroid.