Near or in the permafrost boundary. That clearly shows these previous episodes between ice ages were warmer than this episode we live in today.

Age of Rocks

Caves are among nature’s most meticulous record keepers. Every year, infiltrating rain or snowmelt dissolves the bedrock in which the cavern has formed and deposits minerals inside the cave as iconic formations—stalactites, stalagmites, flowstone, and more—called speleothems. Most importantly, these formations are locked away inside underground refrigerators, so to speak, safe from the surface environment. Using various chemical analyses, geologists can reconstruct past climates from the tiny layers within speleothems, because the chemistry of the rock reflects that of the precipitation that originally fell on the region over thousands of years.

So what happens when water can no longer flow into the cave from the surface? Of course, if a region experienced severe and prolonged drought, there would be no water to infiltrate caves in the first place, and this would result in a paucity of speleothem growth. But there is another phenomenon that can prevent ample rain and snowfall from ever reaching the…

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