From Missing in action? Evaluating the putative absence of impacts by large impacts by large asteroids, and comets during the Quaternary period. –W. Bruce Masse et al, we read,
“ Our understanding of the recent impact record may be inhibited by the necessarily conservative practice of not validating an impact structure unless it exhibits a full suite of impact hallmarks such as uplifted concentric rings, shocked breccias and quartz, and glass and other impact melts.”
I don’t want to be too critical here. The paper is excellent. But I would change that one line “may be inhibited by the necessarily conservative practice”. It should be amended to read “Is inhibited by the overly conservative practice”. A case in point is the Tunguska blast of 1908. The only officially recognized large impact event, indeed, perhaps the most powerful non-terrestrial explosion, in all of recorded history, was an airburst event that did not produce a crater. And, in spite of it’s obviously ET origin, the blast effected materials of that event do not qualify as an impact structure according to that “full suite of impact markers”.
In fact the event didn’t display any of the planetary scarring expected by standard impact theory. And there is a significant, and growing body of compelling evidence that tells us the only thing rare about the Tunguska object is that it arrived alone. A large cloud, or stream of such air bursting fragments is far more likely.
The Deep Impact mission to comet TEMPEL 1 showed the head of that comet to have the consistency of a dirty snow bank. It also showed that the object is a geologically active body. Comet HOLMES is unstable, and prone to violent outbursts. Comet LINEAR , and Comet Scwassmann-Wachmann 3, make it abundantly clear that total, explosive, fragmentation of a comet can occur spontaneously at any time. And it can happen before it even gets close to a planet. It doesn’t need the atmosphere to do that.
The current impact assessments don’t consider airburst ground effects at all. Or impact shower events. So that suite of markers is clearly no where near full. And it is effectively useless.
According to that ‘full suite of markers’, These aren’t impact structures.
Neither are these.
These don’t qualify either.
The worlds most foremost “experts” in impact science readily acknowledge that impact science is very poorly understood. There can be no “experts” in any field which can be accurately described by it’s highest authority as ‘poorly understood’. And yet those same “experts” presume to define a very narrow, and ridged, set of criteria that is considered a “Full suite of markers” by researchers world wide. The overall result is that the NEO impact threat is terribly underestimated.
You can call things like this anything you like. But in the Geophysical world according to me, they are exactly what they seem. And they are all the very same age. Give or take a few seconds.
Here’s a whole bunch more in Crater Fields