This is part three of a three-part series on Earth's climate through time. You can find part one here and part two here.

The ancient Huronian glaciation and the oxygen catastrophe

Have events like Snowball Earth ever happened before? Apparently yes.

1.6 billion years before the Neoproterozoic events there was still the Huronian glaciation. Its cause was the Oxygen Catastrophe (in English, Great Oxidation Event, GOE), which occurred 2.4–2.2 billion years ago. Before this, there was a lot of methane in the earth’s atmosphere (a gas whose greenhouse effect is much more powerful than CO2), but the appearance of oxygen led to the oxidation of CH4 — which resulted in a sharp cooling.

Phanerozoic era: no global glaciations, but significant ice ages

But during the Phanerozoic (which has lasted for the last 542 million years), there were no more global glaciations, although eras of large ice sheets occurred more than once. The last of them began 40 million years ago and continues to this day. The likely reason could be a more favorable location of the land than in Rodinian times. During the era of Phanerozoic glaciations, the continents were located mainly in the middle and high latitudes. On the one hand, this facilitates the process of glacier formation during cold weather. On the other hand, ice sheets are localized in circumpolar regions; the ice does not reach the critical 30th latitude. At the same time, with the higher latitude position of the continents (which are also partially covered by ice), the rate of weathering is relatively low, and the Great Thermostat manages to keep the concentration of CO2 in the atmosphere at a certain level, preventing the planet from cooling too much.

The future of Earth's climate: uncertainty and possibility

Are such events possible in the future? Who knows. In any case, the maximum of the next ice age will occur in about 80 thousand years, so this issue is not very relevant for us yet. Moreover, if CO2 concentrations in the atmosphere remain at current levels (which have already exceeded 410 ppm), then the next ice age will simply not occur.

Finally, we should also mention the possible role of “Snowball Earth” in the development of life on Earth. After the end of the Neoproterozoic glaciations 635 million years ago, the development of multicellular life on Earth accelerated, culminating in the so-called “Cambrian explosion” — the relatively abrupt emergence of many new evolutionary branches of living organisms between 555 and 520 million years ago. It is believed that the impetus for evolution was precisely the global glaciation, during which most of life on Earth was destroyed, and the rest was isolated for a long time and forced to look for ways to survive in various ecological niches.

Mass extinctions have occurred on Earth at least five more times over the past half-billion years, for a variety of reasons. Each time after them, the biosphere was restored in a new form and continued to evolve. We are now living in the era of the sixth mass extinction, of which we are the cause, and the very existence of our own civilization is under threat.

Life, extinction, and evolution: lessons from Earth's geological history

The geological history of the Earth teaches us that our planet has survived everything — most likely, it will cope with this new challenge, with or without us. I would like it to be with us.

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