Together with the carbonate expert Daniel Schrag, Hoffman finally managed to explain the formation of the mysterious rocks – and at the same time the end of the global ice age. They were volcanoes that constantly emitted the greenhouse gas carbon dioxide. Before the ice age, the rain had the CO2 washed into the seas where it was bound as carbonate rock. But now the ice sheet disrupted this important control loop of the Earth system. The proportion of the greenhouse gas increased slowly and steadily, but the light-reflecting ice initially dampened the rise in air temperature. This increased the CO2– Content of the atmosphere to astronomical levels, 20 to 200 times higher than today. When the ice finally retreated, the climate shifted and all hell broke loose.
Worst climate change ever
The world experienced galloping climate change: sea levels rose 1500 meters in just 1000 years – 100 times faster than today. The uncovered sea at the equator readily absorbed solar energy, which accelerated the thawing of the ice. The previously dry atmosphere was saturated with water vapor – and hyperhurricanes raged over seas and barren continents. The falling rain again performed its original function and washed the CO2 from the atmosphere.
Correspondingly, acid rain fell for centuries on landmasses whose surface had previously been battered by glaciers. The rock, ground up by the power of the ice, provided a perfect surface for chemical reactions. The rock flour reacted to carbonate chunks, which now reached the sea in foaming rivulets, streams and rivers. A new blizzard swept down into the oceans, made up of light-colored flakes of carbonate—the remains of decomposed rock dust that had congealed into a layer of mud at the bottom. Eventually the carbonate solidified; only occasionally did trapped gas rise to form the tubes and fan structures that Paul Hoffman found in Namibia.
Initially, geologists opposed Hoffman’s theory of snowball Earth. Again and again they found isolated layers of sediment that seemed to contradict the concept. Some deposits indicated that the glaciers did not reach all the way to the equator and that the ocean continued to exchange with the air there. However, such problems have been resolved over time or reconciled with theory. The globally glaciated planet is considered the most plausible explanation of all geological findings.
How do you survive a mega ice age?
The biggest problem is the development of life: Actually, a mass extinction would have been expected due to the ice – but the diversity of the species decreased only slightly. Even creatures that carry out photosynthesis survived the period of the closed ice sheet – and not only that. Biomarker molecules from the end of the last global ice age indicate that algae replaced the previously dominant cyanobacteria in the seas. Only a few million years later, the first multicellular animal species appeared in the Ediacaran fauna, including the ancestors of modern animals, but also aquatic plankton species, which for the first time devoured other organisms like predators. This development continued to accelerate and finally culminated in the Cambrian Radiation, when the ancestors of almost all modern animal, plant and fungal groups appeared almost simultaneously 540 million years ago.
It is still not clear why Snowball Earth did not eradicate life, but actually accelerated the development of multicellular species. At least that’s what the place is now known for. In addition to deep-sea volcanoes deep below the ice, there were also warmer refuges on the ice: Recent results indicate that although the glaciers surrounded the globe, fluctuations in the earth’s orbit that occurred every few thousand years caused some ice to melt briefly. Scattered liquid water formed, temporarily providing a sheltered home for many species on or beneath the ice, but also isolating them from one another. Perhaps it was precisely the extreme conditions that prompted the unicellular organisms to develop abilities in initially symbiotic communities in order to flee more quickly from all too adverse circumstances.