New Defender's Study Bible Notes
7:4 seven days. This seven-day period of final warning and preparation marks the first of many references to seven-day intervals during the Flood year. This fact makes it obvious that the practice of measuring time in seven-day weeks had been in effect throughout the period between the creation week and the Flood.
7:4 forty days. A worldwide rain lasting forty days would be impossible under present meteorologic conditions. The condensation of the antediluvian vapor canopy, the “waters above the firmament” (Genesis 1:6-8) is the only adequate explanation.
7:4 every living substance. “Every living substance” includes the plant life on the land. The lush vegetation of the pre-Flood world was all to be uprooted, transported and buried in great sedimentary beds, many of which would eventually become the world’s coal beds.