re: Lunar far side
Just curious:
What is the current best estimate of the time of lunar creation?
How long would it take for tidal friction to stop the Moon from spinning, thus establishing a near and far side?
How do those times correlate with the paper's ~3.8 Gya estimate of the geomagnetic field "turning on"?
In other words: Could the Moon have still been rotating during the epoch in question, and if so, what is the probability that far side soils might also have anomalous 14N/15N ratios (if, as hypothesized, the source was ionic "sputtering" from the top of Earth's atmosphere)?