Evidence for a Snowball Earth Imagine a world so barren and so cold that life as we know it today could not exist. Some researchers have been able to track Earth’s glacial deposits to predict just that; a time in which our planet was coated with snow and ice extending from the poles all the way to the equator (Kaufman). We call this period of Earth a “snowball earth.” Scientist Paul Hoffman and his colleagues used Joseph Kirschvink’s suggestion that earth was once completely frozen during the Neoproterozoic period roughly 580-750 million years ago to research glacial deposits. Inherently they found thick deposits of calcium carbonates (cap carbonates) overlaying glaciers suggesting the snowball earth (Hoffman). It is evident in scientific debate that not everyone is able to accept the idea of a frozen Earth as other researchers such as Andrew Knoll and Martin Kennedy have rejected the idea as they pose other solutions for cap carbonate deposits. This is a perfect example of the progress of science as a whole; scientists are constantly making new observations to develop solutions which are then accepted, rejected, and retested by others. The snowball earth hypothesis and controversy together reveals the significance of innovation and scientific debate to the progress of science. The snowball earth hypothesis was first introduced by Joseph Kirschvink after years of other scientists finding peculiar continuous layers of limestone (calcium carbonate rock) or dolostone (magnesian calcium carbonate rock) within other layers of rocks near the equator. These limestone or dolostone layers are called “cap carbonates”, and they form on top of sedimentary rock after major glaciation periods (Hoffman). Therefore, scientists can use observations of cap carbonates to date the time and duration of glaciation periods. Kirschvink suggested that a snowball earth could be the only explanation for cap carbonates reaching the equator and then posed several implications in hope that they would be tested: First, glacial units (evident boundaries between sedimentary rock and cab carbonates) should be continuous around the world. Next, floating ice would have reduced the amount of evaporation because the water would have been trapped underneath the ice. Overtime, ocean currents would have stopped, and all oxygen left would have floated to the top as bubbles. As a result, all life under water would have ceased. Then, ferrous iron from mid-ocean ridges and the ocean floor would have built up in solution and intermingled with glaciers (Hoffman). Therefore, glaciers at that time must have reached sea level leaving scientists with the opportunity to find these glacial deposits on land near the equator. A key analyzation of the Earth’s ice cover to note is as its ice cover begins to move further towards the equator, the Earth’s albedo (proportion of light reflected by the surface) increased. If the ice passed a critical surface area, then the Earth’s albedo would have lowered atmospheric temperature further driving the Earth towards the resemblance of a snowball. Lastly, glacial deposits must have been overlain by thick layers of cap carbonates. Since life at the time had just about ceased, the amount of inorganic carbon isotopes (non-living matter origin) within the cap carbonates would have increased in ratio with organic carbon isotopes (living matter origin) (Hoffman). Since these kind of cap carbonates are generally deposited in warm seas, it would be safe to assume that the Earth’s glaciers reached the equator if found. Kirschvink’s innovative implications left the idea of a snowball earth open for research and debate, a true significance in the progress of science. Kirschvink’s innovative thinking gave way to Paul Hoffman’s research as the next step to the progress of science was to observe what Kirschvink found to be peculiarly interesting. In order to gather data, Hoffman and his team of researchers studied rocks in what used to be the edge of a vast ocean. Today it is the Otavi group of rocks in Namibia. The rock sections that were studied revealed a layer of material that contained both Carbon-13 and Carbon-12 isotopes in the same ratio as in the ancient ocean (Hoffman). This carbon material originally existed in the ocean itself until chemical and biological processes removed it. As the ice layer of the earth approached the equator, the portion of carbon material removed from the earth due to biology decreased rapidly (Kaufman). This suggests that lifeforms at the time were becoming extinct which is concurrent with Kirschvink’s implication. In the sections of rock that were studied, carbon isotope ratios suggest that most biological systems had ceased. There must have been a few breaks in ice or bare patches on ground for multicellular organisms to survive the snowball earth and eventually rise to all life today (Hoffman). Researchers also observed a distinct layer of cap carbonates in the rocks. The only way to explain this is to suggest that calcium dioxide transferred into the of a much warmer and carbon dioxide rich atmosphere. As the earth was in its full glaciation period, carbon dioxide was slowly being let out through volcanic holes. As there was no mechanism to remove this carbon dioxide, its concentration in the atmosphere increased rapidly. Eventually the atmosphere of the earth contained 350 times more carbon dioxide than what exists in the atmosphere today (Hoffman). This high amount of carbon dioxide created a massive greenhouse effect with the sun, resulting in a warming of the earth (Kaufman). This rapid warming of the earth saved life as we know it today. Hoffman and his team proposed a recovery from a snowball earth, suggesting that there was a snowball earth in the first place. Their data was consistent with Kirschvink’s innovative hypothesis that a snowball earth explains observations in geological and geochemical changes, as the fluctuations in carbon isotope ratio values suggests the presence of carbonates directly following a full glaciation period. Although Hoffman had the most complete set of data, the hypothesis of a snowball earth was still up for debate. Other researchers such as Andrew Knoll and Martin Kennedy have suggested other explanations for the presence of cap carbonates and a snowball earth. Knoll suggested that the cap carbonates were deposited from carbonate-rich waters up welling from deep oceans (Knoll). Kennedy argued that if there really was a point in time in which the Earth’s waters were completely ice covered, then strontium isotopes should have responded and fluctuated as well. His data suggests that while the carbon isotopes fluctuated in favor of a snowball earth, strontium isotopes fluctuated in the opposite direction (Hazen). This debate only encouraged Hoffman to continue his research in the discovery of an ancient snowball earth. All in all, the snowball earth hypothesis is still up for debate. Without Kirschvink’s innovative thought which sparked other scientists such as Knoll and Hoffman to research and study ancient glacial deposits, we would know much less about Earth’s ancient deep freeze. The significance of innovation and scientific debate to the progress of science is clearly evident in the search of an ancient snowball earth. Hoffman’s suggestion to the snowball earth is important to the history of living organisms. Such a widespread glaciation would have killed off the weakest of organisms at the time while isolating the strongest organisms. After the Earth’s recovery of its deep freeze, surviving organisms gave way to all life as we know it today. Although it may be clear in Hoffman’s research, the debate will continue to question such a catastrophic event.
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