Impact craters are ubiquitous throughout the solar system – every single solid body has craters on its surface except for the moon Io (because its surface is so young due to the incredible amounts of vulcanism).
Its underlying assumption, unquestioned for decades, has recently been found to be seriously flawed.One writer in estimated that a single large impact on Mars could generate ten million secondaries, and that 95% of the small craters on Europa could be from fallback debris.Without a way to reliably identify secondary craters, only subjective inferences can be made about the history of a surface.Crater-count dating seems perfectly logical: the more craters, the older the landscape.It assumes, however, that impactors arrive at a roughly steady rate and produce one crater per hit.► Increased reliability of crater production functions and consequent age measurements.
Dating methods are like human pyramids; they depend ultimately on the support of the bottom layer. If the bottom guy buckles under pressure, the circus act quickly turns into a dogpile.
After compensating for various complicating factors, like atmospheric density, gravity, and geological activity, scientists had been confident of their time charts -- until recently.
New thinking about "secondary craters" has thrown this whole foundation of comparative planetary dating into disarray.
Believing they knew how old the earth-moon system was, and something about its geological history, scientists had plotted crater density on the moon against surface age.
They applied this to Mars and other planets and moons, such that any surface could be dated by reference to the lunar standard. Now, awareness of the potential for single impacts to generate vast numbers of secondary craters has yanked the guy on the bottom, bringing the scheme crashing down.
In general, this type of analysis may give a better insight into the post-formation modification of studied units, enabling a more precise classification of which sizes of craters derive from the original accumulation population and which from areas resurfaced by later modification events, consequentially improving the accuracy of dating resurfacing events.