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There have been at least four major ice ages in the Earth's past. Outside these periods, the Earth seems to have been ice-free even in high latitudes.
The earliest hypothesized ice age, called the Huronian, was around 2.7 to 2.3 billion years ago during the early Proterozoic Eon.
The earliest well-documented ice age, and probably the most severe of the last 1 billion years, occurred from 850 to 630 million years ago (the Cryogenian period) and may have produced a Snowball Earth in which permanent ice covered the entire globe. This ended very rapidly as water vapor returned to Earth's atmosphere. It has been suggested that the end of this ice age was responsible for the subsequent Ediacaran and Cambrian Explosion, though this theory is recent and controversial.
Sediment records showing the fluctuating sequences of glacials and interglacials during the last several million years.A minor ice age, the Andean-Saharan, occurred from 460 to 430 million years ago, during the Late Ordovician and the Silurian period. There were extensive polar ice caps at intervals from 350 to 260 million years ago, during the Carboniferous and early Permian Periods, associated with the Karoo Ice Age.
The present ice age began 40 million years ago with the growth of an ice sheet in Antarctica. It intensified during the late Pliocene, around 3 million years ago, with the spread of ice sheets in the Northern Hemisphere, and has continued in the Pleistocene. Since then, the world has seen cycles of glaciation with ice sheets advancing and retreating on 40,000- and 100,000-year time scales. The most recent glacial period ended about ten thousand years ago.
Ice ages can be further divided by location and time; for example, the names Riss (180,000–130,000 years bp) and Würm (70,000–10,000 years bp) refer specifically to glaciation in the Alpine region. Note that the maximum extent of the ice is not maintained for the full interval. Unfortunately, the scouring action of each glaciation tends to remove most of the evidence of prior ice sheets almost completely, except in regions where the later sheet does not achieve full coverage. It is possible that glacial periods other than those above, especially in the Precambrian, have been overlooked because of scarcity of exposed rocks from high latitudes from older periods.
The above is from Wikepedia, and I hate being a pest about this. The book referred, and I haven't read it just yet, seems to talk about looking at 100,000 years, yet the total history of climate change is so very much longer. I know nothing about the other forms of proxy data gathering, but as a lay person, you may see my problem. Thanks for indulging.
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