Such things are thought to be left over from the formation of the solar system 4.6 billion years ago, they orbit the Sun somewhat like the planets, and are slowly being swept up by impacting the planets and moons of the solar system. They can also collide with each other, which usually creates more, smaller debris. Because of the high relative velocity between the meteoroid and the Earth a large amount of friction is quickly gener- ated when the object enters the atmosphere, leading to very high temperatures and the accompanying streak of bright light seen around the area. Since the object comes in much faster than the speed of sound, it also generates a sonic boom as it descends to lower, denser regions of the atmosphere. The meteors that one might see at night out in dark, rural areas are no bigger than a grain of sand, and they burn up entirely very shortly upon entering the atmosphere, say at 30 to 60 miles above the ground.
Larger pieces penetrate to lower altitudes.
But beyond that, the sizes of fire- balls in general are known only very roughly. To get down far enough in the atmosphere to generate the sounds heard the meteor must have gotten down to at least about 50,000 feet, or 10 miles up, but it may well have gotten much lower. The exact figure depends on the angle at which it came in and, to some degree, what it was made of. Since a good track could help pin down the area to search in order to make a find, this is the single most important information eye-witnesses can supply. Again, this cannot be determined until witnesses' observa- tions are put together.