Whence the Missing Hadean Rock Record?

Do the various continental crustal growth curves formulated from disparate geochemical models robustly inform us as to why the Hadean (pre-4 Ga) rock record is basically non-existent? Is its absence due to extrinsic effects (bombardment)? Or, could it be that little or no continental crust existed at first? On the other hand, was this record essentially lost over time by recycling processes? For instance, the biggest problem with searching for any information about the history of plate tectonics is that the process erases evidence of its own existence. The age of oceanic crust averages about 70 Ma and is not older than 200 Ma because plate tectonics keeps recycling it (except for some old ophiolites). Most of the crust by surface area is oceanic, whereas most crust by volume is continental. The mean age of continental crust (ca. 2 Ga) is 36× greater than that of oceanic crust because its buoyancy prevents it from subducting except for loss to subduction via erosion. The overall decline in preserved continental crust based simply on the detrital zircon record shows a roughly 1.4 Gyr e-folding time. The residence time of the lithosphere is the average length of time that it will remain as a geochemical entity; this is estimated to be about 500-750 Myr. The value is about half of the observed e-folding time for the pre-Phanerozoic (>542 Ma) continental crust, but is close to the average mixing timescale since the Archean of about 420-440 Myr for primitive mantle, recycled continental crust and mantle residue. Assuming the residence time of 750 Myr is a good estimate for the half-life of continental crust, then the e-folding time is in broad agreement with both the zircon record and model calculations of crustal reworking. The zircon record is strongly biased to continental crust, because zircon is most commonly found in granites and granitoids, which constitute the major rock fraction of the continents.  The trends in the detrital zircon data can be interpreted to represent decreasing preservation rather than increasing production, of continental crust.