There’s an article by The Bad Astronomer about an impact crater that has been found in Greenland. And quite possibly it’s quite new. Maybe as young as 12,000 years.
So how do you date such a crater? With old craters you can date overlying rocks, but this one just has ice over it. Is drilling ice cores feasible?
Well, you bring flowers and ask nicely…
You can date the highest datable layer of strata that the crater cut through. You might could also get a date with doing luminescence dating of debris in the top of the crater.
This site about Barringer Crater has this to say about how it was dated:
From here: BARRINGER IMPACT CRATER – Crater Explorer
The Greenland crater, while under a glacier, is said to have obliterated some bedrock features that were produced by the glacier. Thus the crater is not older than the current glaciation. That may not narrow it down much, but it puts an upper limit on the age.
Drilling ice cores, meanwhile, is not only feasible but routine. That’s one of our main sources of information about the climate in the past.
The article gives a range from 3 million to 12,000 years old - still quite a range. I suppose part of the problem is study opportunities are limited due to location and ice cover, so it may take a while to get a more exact answer.
Under stratigraphic principles the meteor would have to be younger than the impacted surface and older than the infilling event [note that the infill deposit may itself be of considerably older material such as upcast bedrock, but the infilling event is younger].
Assuming the infill is glacial ice, this is dateable. This article gives an excellent explanation of the key techniques. This one less so, although I concur with its brave conclusion that the Earth is at least 160,000 years old.
This article mentions the intriguing idea that this impactor could be the source of the Cape York meteorites.
Ice cores only give you the age of the overlying ice. There may be a gap between crater creation and ice infill.
The absolute best for an exposed crater is, as mentioned in e-c-g’s post, is one of the cosmogenic radionucleide methods, but I don’t know how effective those are for an* ice-covered* crater, as they rely on exposure to cosmic rays for the clock.
Also, note that different methods have windows that only make them useful for impacts in a certain range. Thermoluminescence, for instance, is only really applicable to recent impacts.
I suppose a combo of methods would be best. First and foremost is always going to be stratigraphic analysis. But if you can get either the impact melt or ejecta breccia exposure, then dating becomes a *lot *easier as you could likely date those directly using fission track, thermoluminescence or radiometric dating on stuff you know is the exact same age as the impact.
Here’s an article on impact dating…
I should add a caveat that this applies to ice cores above the impact crater. Obviously, if you take a continuous ice core elsewhere close by, which includes impact ejecta* and goes past it,* you can then date the crater rather precisely. Possibly down to the exact year, give-or-take.
All good stuff, thanks.
Even though this has been answered, I’ll refrain from making the obvious ass/hole in the ground joke.
Oh, as an aside:
I’m not even in, um, the study of meteors (what would that field be called?), but I get a little bit giddy whenever I see three completely independent measures of the same thing that get results that close.
Also there may be clues from very old craters from geological action.