Argument Against The Snowball Earth Hypothesis
The Snowball Earth Hypothesis is not the only one which explains the anomalies discussed earlier, but in my opinion it is the one which takes into account every detail and explains why all of these enigmas happened around the same time. One must, however, consider other points of view and realize that there are other theories. Some geologists have argued that much of the data from the snowball Earth theory can be used to disprove it.
Models have shown that it is impossible to get an ice sheet to grow in low latitudes. If one puts in carbon dioxide levels at 315 ppm (pre-industrial levels), it is impossible for the ice sheets to grow anywhere near such low latitudes. Scientists then tried changing one major factor: the sun. As previously mentioned, the sun was at about 94% of its current luminosity in the Neoproterozoic, so the models were fir to this criteria. This did not change the outcome of the model, because an ice sheet was still not able to grow at low latitudes despite the smaller amount of energy coming in from the sun, according to the model. Scientists then tried lowering the atmospheric levels of carbon dioxide to 40 ppm, which is not very accurate, but they wanted to see if the ice sheets will grow under these conditions. Although the ice sheets got much closer to the tropics, the model still indicated that the ocean was not nearly completely frozen over as the snowball Earth Hypothesis suggests.
Another argument against the snowball Earth are synglacial carbon isotopes. There is now data which shows that the isotope values, although not uniform, tend to be +2 or +3. During the snowball Earth, these values are supposed to be -5, because they should be close to the mantle carbon values since this is the only input of carbon due to the surface being frozen. As one will recognize, these value are very different than what they are supposed to be for a snowball Earth to truly have happened. To add to this, strontium ratios are relatively steady during this supposed glaciation, showing no stopping or abrupt changes in weathering rates.
Because of these contradictions, some geologists have come up with alternate ideas as to what may have happened in the Neoproterozoic to create such anomalies, mainly to explain the strangest of these occurrences: the cap carbonates. Alternative theories include: (1) Post-glacial upwelling, It is difficult to prove this, however, because “it is difficult to stratify a glacial ocean, and upwelling leads to enhanced productivity,” Christie-Blick, April 2002. (2) The Gas Hydrate Hypothesis explains why the isotope of carbon found in the cap carbonates is a rare one. There is evidence which supports this theory, but it does not explain any of the other anomalies which were found.
Although there are many people who do not believe that the snowball Earth really happened, no scientist has been able to come up with a theory that encompasses and explains all of the strange occurrences which left anomalies in the record of the Neoproterozoic. The Snowball Earth Hypothesis explains the iron formations which should not have been there, the glacial debris directly proceeded by carbonate, the cap carbonates, and it even explains the Cambrian explosion of multicellular life. Although this theory has its flaws, unless someone went back in time to see what really happened, the Snowball Earth Hypothesis is the best explanation for what may have happened six hundred million years ago to change our planet forever.
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