Monday Minute: Siberian caves reveal multiple ice ages over the last 1.5 million years

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 cave: permafrost.

Permafrost develops in regions where the average annual temperature is below freezing. Consequently, the ground itself remains frozen year round, along with any water that it contains. Today, permafrost exists mainly at very high latitudes, such as northern Alaska/Canada and northern Siberia, because our global climate is relatively warm. During the ice ages, however, permafrost boundaries extended much further south, and that was the subject of a paper by Vaks et al. (2013).

These authors investigated speleothems from several caves in Siberia that are located near or within the modern permafrost boundary. Knowing only these details, we can formulate their hypothesis ourselves: speleothem growth should have only occurred during warm interglacials, during which permafrost layers melted to allow groundwater infiltration. As it turns out, that’s precisely what the researchers discovered, simply by dating dozens of speleothems from each cave. Speleothem growth ceased during each ice age over the past 500,000 years, due to the advance of permafrost:

Figure 2 from Vaks et al. (2013), showing U-Th dates of speleothems (A) alongside global proxies for past ice ages, such as oxygen isotopes in marine sediments (B), biogenic silica in nearby Lake Baikal (C), Antarctic greenhouse gas records (E-F), and solar radiation (G). Note that speleothems grew only during the warm interglacials (shaded areas), whereas no growth occurred during the ice ages (B; blue numbers) that separated these periods.

Speleothems can be dated very precisely, because Uranium decays at a known rate into Thorium and Lead. Uranium is soluble in surface waters (unlike Th & Pb) and can be incorporated into the calcite mineral that comprises most cave formations. While U-Th dating (used by Vaks et al., 2013) can only be applied to samples less than ~450,000 years old, however, the U-Pb method can date calcite formations up to tens of millions of years old. By utilizing the U-Pb method, therefore, the researchers recently extended their chronology to cover the past 1.5 million years. Their results were consistent with the 2013 paper, documenting more than a dozen intervals where speleothem growth was halted by permafrost advance and more than a dozen intervals where speleothem growth continued as the permafrost melted.

Young-Earth Creationists frequently claim that only one “multi-stage” ice age occurred, shortly after the Flood. Additionally, they claim that speleothems can grow rapidly enough to exist in a young, post-Flood world. But these claims are thoroughly refuted by overlapping records of dozens of ice ages during the Quaternary period and detailed radiometric analysis of cave formations. So-called ‘Flood geologists’ cannot explain the extensive advance and degradation of permafrost zones over thousands of miles, let alone how speleothems could yield dates well beyond 4,500 years old.

Featured Image: Sunset over Lake Baikal in southern Siberia, via Flickr

Advertisement