Number of impacts

A very important question about impacts is: how many impacts happen and how many years pass between two impacts (in other words, with which frequency do they happen?)
About this question, it is necessary to say that from the study of craters around the solar system, scientists have deduced that after a period of intense bombardment in the inner solar system that ended about 3.9 bilion years ago (see the history of the solar system), cratering appears to have continued at a slower, but fairly unifom rate untill today.
To give a first estimation of this odiern frequency for what concerns Earth, two values are needed: it is first of all necessary to know how many Neos of different dimensions surround the Earth and, in a second moment it is necessary to determine the probability of impact by a single object of a given dimension.
Once this two values are known, it is possible to represent the estimated frequency of impacts on Earth as a function of the energy of the impact event

This image represents the estimated frequency of impacts on Earth as a function of their energy .
It is important to understand that this graph only represents a statistical estimation. For example: an event as the KT impact (click here to know more) is estimated to happen every mean period of 100 million years. This doesn't mean that exactly every 100 million years such an event will happen!