"We are like the 13th advanced civilization... or some such"

I am confident we aren't the first. The evidence of identical and unknown techniques of working megaliths in an apparent plastic state is shown on multiple continents, from S. America, N. Africa, S. Asia, and N. Europe, at least, and this strongly suggests a global technologically advanced civilization. Other evidence from S. America and N. Africa in the form of delicate obsidian bobbins and clearly lathed stone, the incredible accuracy and precision of the Serapeum stone boxes, and much more, are utterly inexplicable absent technology to manufacture them in advance of our present capabilities.

While I am unaware of anyone today manufacturing bobbins out of obsidian, I am sure we manufacture equivalent objects of glass today. The problem with obsidian is that it is naturally occurring stone produced in volcanoes, and can't be fabricated in molten form as we do modern glass objects, but must be machined, and to my knowledge there is no means of machining bobbins an inch long and wide with walls ~1mm thick. Any chuck or jaw such an item could be clamped in would shatter it when forces capable of grinding or paring away glass were applied to the rotating blank.

These items clearly were manufactured, so means do exist to do so. Just not means we possess today, or are aware of ever being possessed. While how such things were manufactured remains a mystery, it is certain that such things weren't chipped, chopped, or pounded out of the rocks by Stone Age technologies.

As to what happens when Ice Age glaciers form and accumulate, it seems fairly straightforward, if implacable. Over successive years, ice and snow from the previous winter isn't thawed and drained away, resulting in accumulations that eventually become glaciers. As water is trapped in ice, sea level drops. Shorelines recede and the continental shelves are laid bare to an ever further extent.

Questions arise as to weather conditions during years in which ice and snow accumulates. I know that equatorial heat evaporates ocean water and then that water vapor is transported by currents to polar regions where it is condensed out of the atmosphere and falls to Earth as snow or other forms of frozen water. Whether that snow falls in catastrophic storms that persist for centuries or not is unknown, but given need for significant climactic disruption for such accumulations to be precipitated, and prehistoric events like the Younger Dryas, it seems possible that events comparable to nuclear winters could well be the proximate causes.

I can't think of any nice, pleasant ways to start an ice age, in other words.

Thanks!