I found the introduction to be a very important part in my understanding the following information since it set a scale for the magnitude of important impacts. Some frightening statistics are also presented which show the importance of this type of research and give good reason to continue reading the article. The first question the authors address is that of the flux of the impacts. A quick explanation of the technique used for calculating the flux of the impacts is given. The authors adopt the average flux calculated by Shoemaker and base most of their observations and calculations on these numbers.
Shoemaker gives the average flux of asteroids by the kinetic energy.
It is easy to see that the larger the asteroid the less often an impact occurs. These numbers are one of the important factors in computing the statistics to follow and it made things clearer seeing where the numbers came from. One of the more important questions that is still a topic of discussion for many physicists is the amount of damage various sizes of asteroids can do. Assumptions and approximations must be made and values set for this question in order to compute the statistics desired. The authors introduce using the kinetic energy of bodies rather than the diameter and velocity.