The Huronian Ice Age, also known (tongue-twister alert!) as the Paleoproterozoic glaciation, began around 2.4 billion years ago. For about 300 million years, the region around the current North Pole was continuously frozen; sea ice repeatedly advanced to low latitudes.

2.4 to 2.1 billion years ago

With a duration of around 300 million years, it was the longest ice age in Earth’s 4.5-billion-year history. It was named after Lake Huron in North America, where sedimentary rocks provide important clues about the glacial movements of that time. A possible cause of this ice age is the decrease in atmospheric methane, a key component of the primordial atmosphere and a highly effective greenhouse gas. The likely cause of the methane drop was the "invention" of photosynthesis by cyanobacteria, which gradually increased oxygen levels in the atmosphere. At the end of the Huronian glaciations, the first eukaryotes appeared—organisms with a true nucleus, including mammals and thus humans.

– Text: Ch. Spötl, Univ. of Innsbruck

The Cryogenian period began around 720 million years ago and lasted about 90 million years. Strong evidence suggests that Earth was almost completely glaciated twice during this time—known as “Snowball Earth.”

720 to 630 million years ago*

The second-oldest ice age in Earth's history covers a geologically fascinating time, with two near-global glaciations reaching the equator—also known as "Snowball Earth". The breakup of the supercontinent Rodinia, along with intense flood basalt volcanism, is considered a likely trigger for these dramatic climate shifts. It is probably no coincidence that the first multicellular animal organisms appeared at the end of the Cryogenian.

* The beginning of the Cryogenian 850 Ma ago as shown on the path is based on outdated information. A few years ago, this stratigraphic boundary was moved from 720 Ma (see ICS-GeologicalTimescale2020-03), meaning Gate 3 would need to be adjusted accordingly.

– Text: Ch. Spötl, Univ. of Innsbruck

The Andean-Saharan Ice Age began about 460 million years ago and lasted “only” 40 million years. Evidence of glaciation has been found in present-day South America and North Africa.

460 to 420 million years ago

This geological period, also known as the Hirnantian glaciation, remains puzzling to scientists. Clear evidence of glaciation is found in West Africa and the Andes, which at that time—long before the Atlantic opened—were located near the South Pole. The emergence of land plants is considered a possible trigger for this global cooling and polar glaciation. Before about 460 million years ago, Earth’s land surface was mostly barren (apart from lichens), but the expansion of plant cover significantly accelerated chemical weathering of rocks, reducing atmospheric carbon dioxide and weakening the greenhouse effect.

– Text: Ch. Spötl, Univ. of Innsbruck

This ice age began around 360 million years ago and lasted about 100 million years. The glaciation covered the massive former southern supercontinent Gondwana.

360 to 260 million years ago

Also known as the Permo-Carboniferous ice age, this glaciation occurred near the end of the Paleozoic era and covered a large southern supercontinent known as Gondwana. Gondwana later split into today's continents—Africa, South America, India, Antarctica, and Australia—where traces of this glaciation are still visible (such as in South Africa’s Karoo Desert, hence the name). One likely cause of the global cooling was the preceding Carboniferous period, during which vast amounts of organic material were buried, removing large quantities of carbon from the atmosphere and drastically reducing CO₂ levels—and with it, the greenhouse effect.

– Text: Ch. Spötl, Univ. of Innsbruck

Today we live in a warm phase of the most recent ice age—the Quaternary—which began around 2.6 million years ago. The last cold phase maximum was about 25,000 years ago. We are currently in an interglacial period that started about 11,700 years ago.

2.58 million years ago to present

The most recent ice age is the only one in Earth's history that led to glaciation at both poles (the North Pole itself, being in the ocean, cannot become glaciated, but vast areas of North America, northern Siberia, and of course Greenland can). Quaternary glaciations began about 2.6 million years ago in the Arctic, triggering a climatic rollercoaster of long cold phases and shorter warm periods. We’ve been living in one such warm period for the past 11,700 years, following a cold phase that lasted roughly 100,000 years. That glacial maximum peaked around 25,000 years ago, causing glaciers to expand significantly—also here in the Alps—and lowering the sea level by up to 130 meters.

– Text: Ch. Spötl, Univ. of Innsbruck

The glass plates attached to the steel rings appear in various shades of blue. They are inspired by the cyanometer, a scale developed in the late 18th century to measure the sky’s color intensity. The colored glass filters and reflects sunlight, creating a kind of mini-atmosphere.

Horizon, cardinal directions, solar movement, atmosphere, and the marking of ice ages—all point to the great interconnections of time and space, to the Earth’s development, its climate fluctuations and ice ages, and finally to today’s human-induced climate change and its effects on the alpine environment and retreating glaciers. Even the Hochjochferner/Vedretta del Giogo Alto at the foot of the installation is disintegrating.