I won’t get into the age of the Earth, but a simple high school experiment showed how to cut through an ice cube with a thread and a fishing weight on each end. Ice melts under pressure, freezes after pressure point sinks. Toss a handful of rocks on a frozen pond, they are in craters very soon and sink out of sight. Park a 14,000 lb fighter plane on the ice, it sinks.
Like I noted according to theory it should have sank abouot 3’ and they were originally looking for it at about 3’ down with penetrating radar which is why it was as hard to find as it was i.e. they were looking in the wrong place. A P38 is only heavy if you try to lift it fully loaded, the wing loading was sufficiently light for it to fly at 400 mph and you’d be talking about that same surface sinking through ice which is positively not the same thing as a stone or fishing weight sinking.