The longevity accounts in the Bible, mostly in Genesis, were contested by some, but nevertheless were accepted as valid by such persons as Josephus in the 1st century, Augustine in the 5th century A.D. and the Puritan scientists in the 17th century A.D. WHY was subject not to doubt, but to varying speculations. Recorded in the Bible, especially Genesis, are: (1) greatly extended lifespans, and (2) delayed sexual maturation; and both must be related. Also in the Bible are: (3) an abatement or decline of lifespans after the flood, and (4) yet a phenomenal vigor in the lives of the patriarchs. Observed in nature are: (5) great normal size for most fossil animals, and (6) an abatement or decline in the size of animals in the Pleistocene, which is equated to the post-ice-age, post-flood era. It is theorized here that before the flood the atmosphere was like the present atmosphere in constituents for oxygen, nitrogen and argon, but was different in humidity or water vapor, and especially in carbon dioxide. Contemporary CO2 levels are 330 parts per million, partly due to burning of fossil fuels in our age of petroleum. At the turn of the century it was 290 ppM. However, before the flood atmospheric CO2 is considered to be 5000 ppM, some 15 times the current concentration. The decline in atmospheric CO2 is considered parallel to, and caused by, a decline in temperatures of the oceans. Cold oceans will absorb CO2 out of the atmosphere like a blotter; and it is believed that oceans have dropped in average water temperature from a preflood 60oF to a current 38oF. This is the physical cause for the depletion of atmospheric CO2. A decline in CO2 physiologically results, (specific only to the skin and the brain), in a vasodilation of blood vessels and hence oxygenation of the brain cells. The progressive decline of CO2 and hence the decline of oxygenation of the brain cells, especially of the cells in the hypothalamus in the mid brain, is considered the caue of the accelerated aging. Accelerated aging is believed caused by a more rapid breakdown of the suppression system of the hypothalamus. A more active hypothalamus causes the diseases of aging. This is the hypothalamus disregulation theory. Besides the decline in lifespans as seen in Genesis after the flood, there was also a decline in the age of arrival at sexual maturity, and presumably skeletal maturity. Hence the smallness of contemporary animals compared to fossil ones. The numerical ages of the patriarchs are one class of data. The phenomenal vigor of the patriarchs is seen as supplying a strong internally consistent additional data base, indicating that the data are reliable. Examples are taken in the lives from the 5th, 10th, 15th and 20th generations after the flood in the person of Joktan, Sarah, Job and Caleb. Yet another corroboration in the hypothesis of atmospheric decline in CO2 is seen in the change of ancient climates. North China and Palestine are given as illustration, further underscoring the theory.