Waltham’s models suggest that if the Moon-forming collision had produced a satellite with a radius just 10 kilometers bigger than our Moon, and if the young Earth had turned so that its day was just 10 minutes longer than our Earth, then we would be entering the zone of instability right about now. Or imagine an Earth–Moon system that’s identical to ours in every way except that tidal drag is increased by a few percent; again, we would be just about to enter the zone of instability. Our days would be numbered.
Bilateral effect
