*Includes a bibliography for further reading
The early history of Earth covers such vast stretches of time that years, centuries, and even millennia become virtually meaningless. Instead, paleontologists and scientists who study geochronology divide time into periods and eras. What humans commonly refer to as the "Ice Age" is actually a series of fluctuating climate events that have occurred throughout the planet's history. These ongoing historical phenomena are difficult to conceptualize because of both the time frame involved and the natural process by which they cyclically unfold. The Earth's climatic clock repeats the maneuver over millions of years per occurrence, a number that is intellectually graspable, but not viscerally well-perceivable by most members of the human race. The process by which ice ages form is not relevant to any societal function, and therefore remains a mystery. Those who attempt to define it are often met with either apathy or defiant superstition.
As a basic definition, it may be said that an ice age is simply a period of time during which thick ice sheets cover vast areas of land. These sheets have advanced and retreated, at times taking over the entire planet, and conversely disappearing nearly altogether. Glacial ice formed by this regularly occurring process does not sit in a state of inertia, but moves dynamically, reshaping the geological features of the continents. Again, the time frame for glacial movement is far longer than any involving human activity, so close attention must be paid in order to correctly measure and interpret it for the modern day.
A parallel problem with human perception is that at present, modern society lives in the middle to late period of a relatively gentle, warm vacation from the present ice age. Such brief periods of warmth and climatic stability occur in regular cycles and are known as "interglacials," and for humans, they provide a false sense of calm between the tides of global warming and cooling. Few realize that the comparative balminess of Earth's present climate cycle is exceptional, and likely due to end within just a few thousand years.
The vastly longer "glacial" periods have over time forced early civilizations to evacuate their place of habitation in search of warmer climes, and they also allowed them to return as vegetation and herds of megafauna came back during the warming period that followed. Several species of early hominids have been caught unaware by the oncoming freezing process, and perished for their lack of preparation.
Those who take up either side of the modern debate regarding whether humans affect the ice cycles are probably correct if they allow for a number of likely causes. However, even without us the process continues, regardless of whether human activity has either spurred or delayed the schedule in the most recent centuries. The various ice ages are accompanied by rising and falling degrees of greenhouse gases such as carbon dioxide and methane, in a renewable cycle of glaciation and thaw. That process operates largely apart from human interference despite the reality that we are creators of those gases.

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