New Defender's Study Bible Notes
11:13 four hundred and three years. It is obvious, by comparison of the genealogies and chronologies in Genesis 5 and 11, that the longevity of mankind began a steady decline after the Flood. Undoubtedly the vast climatological and physiographical changes caused by the Flood were the main natural causes of this. The protective vapor canopy was gone (see notes on Genesis 1:6; 7:4), the rich soils were gone, mutations were increasing in the inbreeding populations, and the general environment was much more rigorous. No doubt it was also providentially ordered that, in the post-Flood world, life-spans should settle at around seventy (Psalm 90:10).