The Quaternary glaciation, beginning 2.58Ma, refers to a cycle of glacial-interglacial phases. The onset of the quaternary ice age is defined by the formation of the Arctic ice cap. There have been very few glacial periods over the last 2.5Ga of the Earth’s history and they are highly infrequent (a brief overview glacial history can be found here), the last ice age before the Quaternary took place during the Carboniferous (see post on the CRC).
The Quaternary ice age has seen substantial fluctuations in global sea level and ice volume, with the coldest periods having ice sheets kilometres thick across Europe, North America and Siberia. However, these cold periods are permeated by warmer interglacial phases, evidenced by peat beds and lacustrine deposits separating unsorted deposits of glacial debris. Despite the cyclic nature of the Quaternary, it is generally referred to as an ice age, seeing that at least one ice sheet has existed continuously.
The exact cause of the Quaternary ice age is controversial. Milankovitch cycles remain a popular theory for smaller climatic cycles e.g. glacial and interglacial periods, yet the Milankovitch cycles have been operating for millions of years and glaciation has remained a rare occurrence throughout history, so this alone is problematic for explaining the Quaternary glaciation.
Another proposed theory is a drop in global carbon dioxide levels, this has been observed over the course of the Cenozoic, but also prior to the Antarctic glaciation. Whilst CO2fluctuations are congruent with glacial-interglacial cycles, correlation does not equal to causation. There is a link between decreasing CO2 levels and cooling climate throughout the Cenozoic, CO2variations may instead be a result of glaciations, rather than a cause of them.
As with the glaciation of Antarctica, plate tectonics and disruptions of ocean circulation may have been a factor triggering the Quaternary glaciation. The Isthmus of Panama opened 2.8Ma, just before the onset of the Quaternary glaciation connecting North and South America. This closed any remaining waterways outside of the polar latitudes that allowed interchange between the Atlantic and Pacific oceans, this had a cooling effect on the climate.
Large scale glaciation led to the formation of many large freshwater lakes across the globe (as a result of decreasing sea level), as well as disrupting oceanic and atmospheric circulation globally, having a major influence of global weather patterns.
Modern humans and animals evolved in an icehouse world permeated by interglacial periods. With global warming threatening the existence of the poles, our existence as we know it will change forever. Therefore, I think it is vital that we understand the causes and effects of the Quaternary glaciation in order to better prepare for our future which, for the first time in our history, may be absent in ice sheets and to anticipate how modern species will be affected by a warming climate.
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