the Quaternary, variance became more and more extreme. Looking back over records of the past million years, geologists estimate that there were at least 40 cold or glacial intervals, and these were of varying length and were not regular in occurrence. In the last 400,000 years of the Ice Ages, proxy data indicate that there were four extreme cool periods (glacials) interspersed with five variable warm periods (interglacials). The last major interglacial (spanning the interval of about 80,000-122,000 years before present) was similar in warmth to the present interglacial climate, but the previous interglacials were definitely cooler that the present one.
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